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Vandamme, Nicolas. "Nanostructured ultrathin GaAs solar cells." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112111/document.
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L’amincissement des cellules solaires semi-conductrices est motivé par la réduction des coûts de production et l’augmentation des rendements de conversion. Mais en deçà de quelques centaines de nanomètres, il requiert de nouvelles stratégies de piégeage optique. Nous proposons d’utiliser des concepts de la nanophotonique et de la plasmonique pour absorber la lumière sur une large bande spectrale dans des couches ultrafines de GaAs. Nous concevons et fabriquons pour ce faire des structures multi-résonantes formées de réseaux de nanostructures métalliques. Dans un premier temps, nous montrons qu’il est possible de confiner la lumière dans une couche de 25 nm de GaAs à l’aide d’une nanogrille bidimensionnelle pouvant servir de contact électrique en face avant. Nous analysons numériquement les modes résonants qui conduisent à une absorption moyenne de 80% de la lumière incidente entre 450 nm et 850 nm. Ces résultats sont validés par la fabrication et la caractérisation de super-absorbeurs ultrafins multi-résonants. Dans un second temps, nous appliquons une approche similaire dans le but d’obtenir des cellules photovoltaïques dix fois plus fines que les cellules GaAs records, avec des absorbeurs de 120 nm et 220 nm seulement. Un miroir arrière nanostructuré en argent, associé à des contacts ohmiques localisés, permet d’améliorer l’absorption tout en garantissant une collecte optimale des porteurs photo-générés. Nos calculs montrent que les densités de courant de court-circuit (Jsc) dans ces structures optimisées peuvent atteindre 22.4 mA/cm2 et 26.0 mA/cm2 pour les absorbeurs d’épaisseurs respectives t=120 nm et t=220 nm. Ces performances sont obtenues grâce à l’excitation d’une grande variété de modes résonants (Fabry-Pérot, modes guidés,…). En parallèle, nous avons développé un procédé de fabrication complet de ces cellules utilisant la nano-impression et le transfert des couches actives. Les mesures montrent des Jsc records de 17.5 mA/cm2 (t=120 nm) et 22.8 mA/cm2 (t=220 nm). Ces résultats ouvrent la voie à l’obtention de rendements supérieurs à 20% avec des cellules solaires simple jonction d’épaisseur inférieure à 200 nmThe thickness reduction of solar cells is motivated by the reduction of production costs and the enhancement of conversion efficiencies. However, for thicknesses below a few hundreds of nanometers, new light trapping strategies are required. We propose to introduce nanophotonics and plasmonics concepts to absorb light on a wide spectral range in ultrathin GaAs layers. We conceive and fabricate multi-resonant structures made of arrays of metal nanostructures. First, we design a super-absorber made of a 25 nm-thick GaAs slab transferred on a back metallic mirror with a top metal nanogrid that can serve as an alternative front electrode. We analyze numerically the resonance mechanisms that result in an average light absorption of 80% over the 450nm-850nm spectral range. The results are validated by the fabrication and characterization of these multi-resonant super-absorbers made of ultrathin GaAs. Second, we use a similar strategy for GaAs solar cells with thicknesses 10 times thinner than record single-junction photovoltaic devices. A silver nanostructured back mirror is used to enhance the absorption efficiency by the excitation of various resonant modes (Fabry-Perot, guided modes,…). It is combined with localized ohmic contacts in order to enhance the absorption efficiency and to optimize the collection of photogenerated carriers. According to numerical calculations, the short-circuit current densities (Jsc) can reach 22.4 mA/cm2 and 26.0 mA/cm2 for absorber thicknesses of t=120 nm and t=220 nm, respectively. We have developed a fabrication process based on nano-imprint lithography and on the transfer of the active layers. Measurements exhibit record short-circuit currents up to 17.5 mA/cm2 (t=120 nm) and 22.8 mA/cm2 (t=220 nm). These results pave the way toward conversion efficiencies above 20% with single junction solar cells made of absorbers thinner than 200 nm
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Tutu, F. K. K. "InAs/GaAs quantum dot solar cells." Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1430283/.
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Self-assembled III-V quantum dots (QDs) have been intensely studied for potential applications in solar cell (SC) devices in order to increase power conversion efficiency. Due to their quantum confinement of carriers, QDs have been proposed as a means of implementing the intermediate band solar cell (IBSC). The IBSC concept is characterised by in an increase in photocurrent and a preservation of output voltage, resulting from an enhanced sensitivity to the solar spectrum. The work reported in this thesis is concerned with the development of InAs QDs in GaAs p-i-n solar cell structures, with the aim of realising of an IBSC. The work involves the design, epitaxial growth by molecular beam epitaxy (MBE), device processing and characterisation of the QDSCs. This thesis first investigates InAs/InGaAs dot-in-a-well (DWELL) solar cell structures grown under different conditions. The use of a high-growth-temperature GaAs spacer layers is demonstrated to significantly enhance the performance of the multilayer DWELL solar cells. Threading dislocations were observed for a 30-layer QD structure with GaAs spacer layers grown at a low temperature (510 oC). By growing the GaAs spacer layer at a higher temperature (580 oC), the formation of threading dislocations were suppressed, resulting in enhanced optical properties. The thesis then goes on to address the main challenges facing QD IBSCs, that is, the reduction in open-circuit voltage and the lack of significant increase in short-circuit current. To eliminate the wetting layer and enhance the open-circuit voltage of the QD solar cell, an AlAs cap layer technique was used. This resulted in an enhancement of the open-circuit voltage of a 20-layer InAs/GaAs QDSC from 0.69 V to 0.79 V. Despite a slight reduction in short-circuit current, for the QDSC with AlAs cap layer, the enhancement in the open-circuit voltage was enough to ensure that its efficiency is higher than the QDSC without AlAs cap layers. In an attempt to enhance the short-circuit current, an antimony-mediated growth approach was used to grow high-density QDs. After optimisation of the growth temperature and InAs coverage, a very high in-plane QD density of 1 1011 cm-2 was achieved by applying a few monolayers of antimony prior to QD growth. Compared with a reference QDSC without the incorporation of antimony, the high-density QDSC demonstrates a distinct improvement in short-circuit current from 7.4 mA/cm2 to 8.3 mA/cm2. This result shows that a significant increase in short-circuit current could potentially compensate for the drop in open-circuit voltage observed in InAs/GaAs QD solar cells. Ongoing work on the development of QDSCs with both AlAs capping and antimony-mediated growth have resulted in the simultaneous elimination of the wetting layer and increase in QD absorption in a single device. Overall, the studies in this thesis present important implications for the design and growth of InAs/GaAs QD solar cell structures for the implementation of IBSCs.
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Chen, Hung-Ling. "Ultrathin and nanowire-based GaAs solar cells." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS355/document.
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Confiner la lumière dans un volume réduit d'absorbeur photovoltaïque offre de nouvelles voies pour les cellules solaires à haute rendement. Ceci peut être réalisé en utilisant des nanostructures pour le piégeage optique ou des nanofils de semi-conducteurs. Dans une première partie, nous présentons la conception et la fabrication de cellules solaires ultra-minces (205 nm) en GaAs. Nous obtenons des résonances multiples grâce à un miroir arrière nanostructuré en TiO2/Ag fabriqué par nanoimpression, résultant en un courant de court-circuit élevé de 24,6 mA/cm². Nous obtenons le record d’efficacité de 19,9%. Nous analysons les mécanismes des pertes et nous proposons une voie réaliste vers un rendement de 25% en utilisant un absorbeur de GaAs de 200 nm d'épaisseur seulement. Dans une deuxième partie, nous étudions les propriétés de nanofils en GaAs crûs sur substrats Si et nous explorons leur potentiel comme absorbeur photovoltaïque. Un dopage élevé est souhaité dans les cellules solaires à nanofils en jonction coeur-coquille, mais la caractérisation à l'échelle d'un nanofil unique reste difficile. Nous montrons que la cathodoluminescence (CL) peut être utilisée pour déterminer les niveaux de dopage de GaAs de type n et p avec une résolution nanométrique. Les semi-conducteurs III-V de type n présentent une émission décalée vers le bleu, à cause du remplissage de la bande de conduction, tandis que les semi-conducteurs de type p présentent une émission décalée vers le rouge due à la réduction du gap. La loi de Planck généralisée est utilisée pour fitter tout le spectre et ainsi évaluer quantitativement le niveau de dopage. Nous utilisons également la polarimétrie de CL pour déterminer sélectivement les propriétés de phases wurtzite/zinc-blende d'un nanofil unique. Nous montrons enfin des cellules solaires fonctionnelles à nanofils de GaAs. Ces travaux ouvrent des perspectives vers une nouvelle génération de cellules photovoltaïquesConfining sunlight in a reduced volume of photovoltaic absorber offers new directions for high-efficiency solar cells. This can be achieved using nanophotonic structures for light trapping, or semiconductor nanowires. First, we have designed and fabricated ultrathin (205 nm) GaAs solar cells. Multi-resonant light trapping is achieved with a nanostructured TiO2/Ag back mirror fabricated using nanoimprint lithography, resulting in a high short-circuit current of 24.6 mA/cm². We obtain the record 1 sun efficiency of 19.9%. A detailed loss analysis is carried out and we provide a realistic pathway toward 25% efficiency using only 200 nm-thick GaAs absorber. Second, we investigate the properties of GaAs nanowires grown on Si substrates and we explore their potential as active absorber. High doping is desired in core-shell nanowire solar cells, but the characterization of single nanowires remains challenging. We show that cathodoluminescence (CL) mapping can be used to determine both n-type and p-type doping levels of GaAs with nanometer scale resolution. n-type III-V semiconductor shows characteristic blueshift emission due to the conduction band filling, while p-type semiconductor exhibits redshift emission due to the dominant bandgap narrowing. The generalized Planck’s law is used to fit the whole spectra and allows for quantitative doping assessment. We also use CL polarimetry to determine selectively the properties of wurtzite and zincblende phases of single nanowires. Finally, we demonstrate successful GaAs nanowire solar cells. These works open new perspectives for next-generation photovoltaics
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Feteha, Mohamed Yousef Mohamed. "Heterojunction AlGaAs-GaAs solar cells for space applications." Thesis, University of Central Lancashire, 1995. http://clok.uclan.ac.uk/18836/.
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Two types of solar cell AlGaAs-GaAs structures which are heteroface and triple heterojunction are investigated in this study. A complete theoretical study including optimisation for the optical properties ( transmission and reflection) of the heteroface Alo.sGao.2As- GaAs space solar cell is presented. The grid shadow and window layer effects, angle of incidence and the effects of the layer design parameters for AR-coating and window layer on the optical properties are considered in the calculations. A new structure for space solar cell which consists of double heterojunction AlGaAsGaAs structure with GaAs/AlGaAs heterojunction back surface field (triple heterojunction(TIIJ))-to enhance the performance of the existed double heterojunction solar cell- is proposed. The analytical model for this TIU cell is presented as a function of all the cell's design parameters ( such as _layers doping, thicknesses, etc). The calculated results for this structure is compared with the experimental results for the previous double heterojunction structure. The effects of the design parameters of all layers including the AR-coating on the cell's output performance and the optimisation conditions are studied as well. The techniques of the light trapping and the photon recycling( which are gocxl for space solar cells) are applied for the THJ thin film AlGaAs-GaAs structure to improve further the efficiency . The change of the optimisation conditions due to the usage of these two techniques is also discussed.
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Robertson, Kyle. "Optoelectronic Device Modeling of GaAs Nanowire Solar Cells." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39710.
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Nanowire solar cells have great potential as candidates for high efficiency, next-generation solar cell devices. To realize their potential, accurate and efficient modeling techniques en- compassing both optical and electrical phenomena must be developed. In this work, a coupled optical and electronic model of GaAs nanowire solar cells was developed, with the goal of building a platform for automated, algorithmic device optimization.
Significant work was done on the optical portion of model, with the goal of reducing run- times and improving the level of automation. Enhancements were made to an open-source implementation of the Rigorous Coupled Wave Analysis method for solving Maxwell’s equations, to make it more accurate for modeling nanowire solar cells. Its accuracy and efficiency were thoroughly investigated, and with the enhancements presented here it was shown to be an effective technique for rapid optical modeling of nanowire devices. Purely optical optimizations of a sample AlInP-passivated GaAs nanowire on a GaAs substrate were performed to demonstrate the efficacy of the technique using a Nelder-Mead simplex optimization of device geometry.
The optical model was then coupled into a finite volume method based electrical model implemented in TCAD Sentaurus, to compute device efficiencies and ultimately optimize electrical device performance. As a first step, an algorithmic optimization of a p-i-n nanowire solar cell consisting of an AlInP-passivated GaAs nanowire on a Si substrate was performed using the generation rates computed by the enhanced RCWA implementation. The overall geometry was fixed to the result of the optical optimization, and only internal electrical parameters were optimized. The results showed that significant performance improvements can be obtained with the right choice of doping levels and doping region configurations, even without optimizing the global device geometry.
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SCACCABAROZZI, ANDREA. "GaAs/AlGaAs quantum dot intermediate band solar cells." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2013. http://hdl.handle.net/10281/40117.
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This thesis presents my Ph.D. work about quantum dot GaAs/AlGaAs solar cells grown by droplet epitaxy, exploring the potential of this materials system for the realization of intermediate band photovoltaic devices. In the first chapter a general introduction to the field of solar energy is given, outlining the reasons why this research has been performed. The physics of the photovoltaic cell is briefly explained in its most important points, to give the reader clear understanding of what is presented in the following chapters. Intermediate band devices are presented in the second chapter. The theoretical foundations presented do not aim at constituting an exhaustive explanation of the theory underlying intermediate band solar cells, but the scope is again to give clear understanding of the characterization of the quantum dot devices reported in the following chapters. A survey of the state of the art in the field is given, pointing out the differences with our technology. The initial part of my Ph.D. work was spent in developing the technology to design and grow (Al)GaAs photovoltaic devices, as well as the characterization techniques required to understand the behavior of such devices. In chapter 3 the method developed to design the solar cell structure is illustrated, and in chapter 5 the experimental setup used for characterization is presented, along with the measurements on the single junction devices realized during this work. Chapter 4 is dedicated to the description of the growth and fabrication methods used to grow the samples reported here. The development of the fabrication technology proceeded in close contact with the characterizations of the devices, in order to optimize the process. Finally in chapter 6 the results on quantum dot photovoltaic cells are reported: the key working principles of intermediate band devices have been demonstrated with our materials system, and this, to the knowledge of the author, is the first time that strain free quantum dot solar cells are reported of intermediate band behavior. The role of defects in the AlGaAs matrix is explained in connection with both the optical and electrical characterizations presented.
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KHALILI, ARASTOO. "Numerical study of InAs/GaAs quantum dot solar cells." Doctoral thesis, Politecnico di Torino, 2018. http://hdl.handle.net/11583/2712032.
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Solar energy conversion is a promising way to provide future energy demand since it is a clean energy. Unfortunately, the photovoltaic (PV) conversion of the solar energy is expensive, therefore, making attempts to increase the efficiency of PV is essential. A conventional single junction solar cell presents an efficiency limit that is determined by the Shockley-Queisser detailed balance principle (i.e. 40.7% under full sun concentration). The limit comes from the fact that only photons with energy close to the energy bandgap are efficiently converted. Below energy gap, photons are not absorbed since the cell is transparent to them and high energy photons only contribute part of their energy that is equal to the energy bandgap. Many concepts have been developed in order to increase the efficiency limit of solar cells. Among them the intermediate band solar cell (IBSC) has gained considerable attention. In principle, IBSCs have the potential to overcome Shockley-Queisser (SQ) limit of single junction solar cells by providing high current while preserving large voltage. The theoretical limit calculated for an ideal IBSC under full sun concentration is 63.1%.
One of the most promising ways to realize the IBSC is to incorporate a QD superlattice in the active region of p-i-n single junction solar cells. The nano-size QDs behave like 3D potential well for the carriers and create discrete energy levels within the forbidden bandgap that allows sub-bandgap photon absorption. Stranski-Krastanov (S-K) growth mode (also called 'layer-plus-island growth') is one of the most common methods to fabricate QDs. This method has been used in many experimental studies for InAs/GaAs heteroepitaxial system which has lattice mismatch of 7.2%. Although InAs/GaAs is not an optimal material system for the IBSC performance, its properties and parameters are well reported in literature compared to other material systems.
The drift-diffusion model is the most widely used mathematical approach to describe semiconductor devices. However, in case of quantum dot solar cells, the physics governing the device performance is not sufficiently covered and up to now, modeling of QDSCs has been treated as IBSC modeling through detailed balance principle and semi-analytical or numerical drift diffusion approaches.
In this dissertation, QDSCs are investigated in detail by numerical simulation using a QD-aware physics-based model. The influence of selective doping in QDSCs is investigated considering different scenarios in terms of crystal quality. Regarding high-quality crystal, close to radiative limit, large open circuit voltage recovery is predicted in doped cells, due to the suppression of radiative recombination through QD ground state. In case of defective crystal, significant photovoltage recovery is also attained owing to the suppression of both non-radiative and QD ground state radiative recombination. The interplay between non-radiative and QD radiative recombination channels, and their interplay with respect to doping are analyzed in detail. Moreover, a numerical study on the influence of wetting layer states on the photovoltage loss of InAs/GaAs quantum dot solar cells is presented. Almost full open circuit voltage recovery is predicted by combining wetting layer reduction and selective doping.
After investigating the inherent limitations of InAs/GaAs QD solar cells regarding realization of the IBSC, a brief description of QDs with type-II staggered band alignment based on GaSb/GaAs material systems (whose interband and intraband dynamics are more promising in view of attaining the IB operating regime) is given and a preliminary study of the competition between thermal and optical escape processes is presented.
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Hardingham, Christopher Mark. "GaAs and GaAs/Ge solar cells : a device and materials study using SEM-EBIC." Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267028.
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James, Asirvatham Juanita Saroj. "Characterization of type-II GaSb quantum rings in GaAs solar cells." Thesis, Lancaster University, 2015. http://eprints.lancs.ac.uk/80244/.
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The use of nanostructured materials in solar cells enables one to tune their absorption properties leading to a better match to the solar spectrum and subsequently an increased photocurrent through the solar cell. Type II GaSb/GaAs quantum rings (QRs) can significantly extend the spectral response beyond the visible out towards 1.4 µm giving a near optimum band gap for concentrator solar cell applications. Also, in type II band alignment the electrons are weakly localized and the built in electric field drifts the electrons across the depletion region easily. However, the introduction of GaSb QRs in GaAs solar cells degrades the open circuit voltage (Voc) and the incorporation of QRs needs to be optimized to minimize the Voc degradation while maximizing short circuit current density (Jsc) enhancement due to sub-bandgap absorption. The analysis of the photoresponse under the white light illumination has shown that some photogenerated minority holes from the base region can be re-captured by the QRs, which reduces the Jsc and the Voc. Hence, in this thesis, the carrier dynamics and extraction mechanisms occurring in the GaSb QRs is investigated by photoluminescence spectroscopy and current voltage characteristics. The characteristic S-shaped behaviour of the WL peak energy with increasing temperature indicates the prominent carrier trapping in the band tail states leading to potential fluctuations. Systematic measurements of dark current versus voltage characteristics are carried out from 100 to 290 K. Compared with the reference GaAs solar cell, the QRSC exhibits larger dark current, however its ideality factor n is similar at 290 K. QRs are directly probed by using an infrared laser (1064 nm) where the photon energy is conveniently chosen below the bandgap of the GaAs matrix. This enables to investigate the carrier dynamics and extraction mechanisms occurring in the GaSb QRs under a high light concentration. The dependence of the photocurrent on the laser intensity, the bias and the temperature is also discussed. The QR photocurrent exhibits a linear dependence on the excitation intensity over several decades. The thermal activation energy was found to be weakly dependent on the incident light level and increased by only a few meV over several orders of excitation intensity. The magnitude of the relative absorption in QRs when directly probed by using a 1064 nm laser with an incident power density of ~ 2.6 W cm−2 is found to be ~ 1.4 × 10−4 per layer. The thermal escape rate of the holes was calculated and found to be ~ 1011 to 1012 s −1 , which is much faster than the radiative recombination rate 109 s −1 . This behaviour is promising for concentrator solar cell development and has the potential to increase solar cell efficiency under a strong solar concentration. Experiments have shown that QDs embedded in the depletion region could generate both additional photocurrent and dark current. The electron-hole recombination in QDs is the reason for the additional dark current which reduces the open circuit voltage and keeps the conversion efficiency of QD solar cells below the ShockleyQueisser limit. Therefore, the reduction in open circuit voltage and the influence of the location of QR layers and their delta doping within the solar cell is investigated in this work. Devices with 5 layers of delta doped QRs placed in the intrinsic, n and p regions of a GaAs solar cell are experimentally investigated and the deduced values of Jsc, Voc, Fill factor (FF), efficiency (η) are compared. A trade-off is needed to minimize the Voc degradation while maximizing the short circuit current density (Jsc) enhancement due to sub-bandgap absorption. The voltage recovery is attributed to the removal of the QDs from the high field region which reduces SRH recombination. The devices with p or n doped QDs placed in the flat band potential (p or n region) show a recovery in Jsc and Voc compared to devices with delta doped QDs placed in the depletion region. However there is less photocurrent arising from the absorption of sub-band gap photons. Furthermore, the long wavelength photoresponse of the n doped QRs placed in the n region shows a slight improvement compared to the control cell. The approach of placing QRs in the n region of the solar cell instead of the depletion region is a possible route towards increasing the conversion efficiency of QR solar cells. The effect of the introduction of dopants on the morphology of GaSb/GaAs nanostructures is analyzed by HAADF-STEM. The results show the presence of welldeveloped GaSb QRs in both p-doped and n-doped heterostructures. However, in the undoped sample grown under the same conditions such well-developed QRs have not been observed. It is found that p-doping with Be stimulates the formation of QRs, whereas n-doping with Te results in the formation of GaSb nanocups. Therefore, the introduction of dopants in the growth of GaSb nanostructures has a significant effect on their morphology. Bias and temperature dependent EQE measurements are performed to understand the hole extraction from the QRs. In order to study the absorption strength of quantum dots and the various transition states, an approach to derive the below-bandgap absorption in GaSb/GaAs self-assembled quantum ring (QR) devices using room temperature external quantum efficiency measurement results is presented. The importance of incorporating an extended Urbach tail absorption in analyzing QR devices is demonstrated. The theoretically integrated absorbance via QR ground states is calculated as 1.04 ×1015 cm -1 s -1 , which is in a reasonable agreement with the experimental derived value 8.1 ×1015 cm-1 s -1 . The wetting layer and QR absorption contributions are separated from the tail absorption and their transition energies are calculated. Using these transition energies and the GaAs energy gap of 1.42 eV, the heavy hole confinement energies for the QRs (320 meV) and for the WL (120 meV) were estimated.
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Pelati, Daniel. "Elaboration of GaAs solar cells based on textured substrates on glass." Electronic Thesis or Diss., Sorbonne université, 2019. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2019SORUS456.pdf.
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Les cellules solaires à base de GaAs détiennent le record d’efficacité pour les architectures à simple jonction, mais le coût des substrats GaAs monocristallins restreint fortement leur utilisation. Dans ce travail, nous avons fabriqué des substrats alternatifs pour la croissance de GaAs, basés sur la combinaison d’un support en silice et d’un film mince (20 nm) de Germanium. Ce dernier est presque à l’accord de maille avec le GaAs et on peut obtenir une texture (111) prononcée en utilisant le procédé de cristallisation induite par un métal (MIC). La texture cristalline est très dépendante des conditions de dépôt et de recuit, ce qui a nécessité le développement d’un microscope in situ pour suivre et optimiser cette étape. Nous avons identifié deux mécanismes de cristallisation, dont l'un perturbe celui qui est responsable de l’orientation (111). Nous avons ensuite réalisé la croissance de GaAs sur ces surfaces de Ge texturées par épitaxie par jets moléculaires (MBE). Nous avons identifié les conditions nécessaires à l’obtention sur Ge(111) de couches de GaAs sans macle ni autre défaut étendu. Les couches de GaAs obtenues présentent une polarité (111)A plutôt que l’orientation (111)B habituellement observée. Enfin, nous avons fabriqué des cellules solaire GaAs orientées (111)B avec un rendement photovoltaïque de 15,9 %. Le transfert de cette cellule sur des substrats Ge(111) et sur nos couches de Ge texturées sur silice révèle un dopage difficile, lié à l’orientation (111)A du GaAs, et une rugosité de surface importante induite par les joints de grain présents dans la couche de Ge initialeThe increasing demand for clean energy has driven research toward higher efficiency and lower cost solar cells. Gallium arsenide solar cells detain the record efficiency for single junction devices but the high cost of the substrate limits their applications. In this work, we investigate an alternative GaAs substrate based on a low cost silica support coated by a thin (20 nm) Germanium layer. This layer is nearly lattice-matched to GaAs and can be crystallized with a high (111) texture using Metal Induced Crystallization (MIC). However, this requires a careful optimization of the deposition and annealing parameters. Here, we use a specially designed in situ optical microscope to optimize the annealing sequence. In particular, we identified two crystallization pathways, of which one should be minimized to obtain a good (111) crystalline texture. We then perform the heteroepitaxy of GaAs on this Ge seed layer using Molecular Beam Epitaxy, keeping the initial (111) crystal texture. We identify specific growth conditions for the twin- and defect-free growth of GaAs on Ge(111) surfaces. We also observe the growth of GaAs adopting the (111)A polarity on Ge (111) rather than the expected (111)B orientation. Finally, we fabricate (111)-oriented GaAs solar cells with 15,9% efficiency on a monocrystalline GaAs(111)B substrate. The transfer to standard Ge(111) monocrystalline wafers and to our Ge-coated silica pseudo-substrates reveals doping issues related to the (111)A orientation of the GaAs, as well as surface roughening due to grain boundaries in the initial Ge seed layer
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Boucher, Jason. "Studies of GaAs Solar Cells Grown by Close-Spaced Vapor Transport." Thesis, University of Oregon, 2017. http://hdl.handle.net/1794/22284.
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While photovoltaic (PV) manufacturing is on track to provide a substantial portion of world electricity generation, the growth of the industry is likely to be lower than desired to meet targets designed to mitigate climate change. Many different PV technologies have been developed, but PV modules based on Si are the dominant technology due to its low cost and relatively high energy conversion efficiencies. PV modules based on III-V materials are primarily used for aerospace applications due to their high cost and record-setting efficiencies. Traditional manufacturing techniques for III-V PV require expensive precursors, and have high capital costs and low throughput. Close-spaced vapor transport (CSVT) is an alternative technique for deposition of III-V materials that was invented in the 1960s but has not been fully developed for the production of PV devices. This work describes progress towards high efficiency solid-state GaAs solar cells produced by CSVT.
Previous results have demonstrated good electronic quality of CSVT GaAs using photoelectrochemical cells, but such devices have not been demonstrated to be commercially practical. This work investigates the potential of CSVT to produce high-efficiency III-V PV by fabricating and characterizing GaAs films and simple homojunction solar cells. Chapter I describes the motivation and state of III-V PV research, and establishes basic device physics background. Chapter II gives details of film growth and device design and fabrication. Chapter III gives an overview of the film and device characterization methods employed. Chapter IV explores the primary limitations in the efficiency of the homojunction solar cells fabricated for this study and discusses some practical concerns in translating the technique to a manufacturing environment. Chapter V explores the electronically-active defects in both $n$-type films and in $p$-type absorbers of solar cells, which would be likely to limit the efficiency of devices optimized considering the results presented in Chapter IV. Chapter VI discusses some of the possible future directions for applying CSVT to more advanced device structures which are more commercially relevant, including the growth on alternative substrates and growth of ternary materials for passivating layers or multijunction cells.
This dissertation includes previously published and unpublished co-authored material.
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Royall, B. "GaInNAs/GaAs multiple quantum well and n-i-p-i solar cells." Thesis, University of Essex, 2011. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.549286.
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Deng, Zhuo, and 鄧卓. "Luminescence and transport processes of charge carriers in the GaxIn₁-xP/GaAs double-junction tandem solar cells." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/211134.
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Semiconductor multijunction solar cell is a cutting-edge photovoltaic technology aimed at developing a frontier solution to the clean energy demand and environmental problem. Due to the efficient photoabsorption and energy conversion in the visible and near-infrared spectral ranges of the solar spectrum, the multijunction solar cell structures have shown an unprecedented application potential by demonstrating a solar conversion efficiency of over 44 %. Among various multijunction solar cell structural designs, the GaxIn1-xP/GaAs double-junction tandem structure is considered as the most fundamental building block for developing the industry-standard triple- and even more junction photovoltaic cells with super high efficiency. Therefore, obtaining a better and more in-depth understanding of physical properties of the GaxIn1-xP/GaAs double-junction tandem device structure, especially some fundamental optoelectronic processes in the individual structural layer, including photoexcitation, transport and the mid-way recombination of charge carriers, is crucial for further improving the energy conversion efficiency. In this thesis, the mid-way radiative recombination, diffusion transport, localization mechanism, and photocurrent spectra of charge carriers in the GaxIn1-xP/GaAs double-junction tandem solar cells grown on GaAs substrates with different misorientation angles were investigated in detail.
Our main findings are summarized as below. Efficient radiative recombination of carriers in the GaxIn1-xP/GaAs double-junction tandem solar cell samples was demonstrated by using electroluminescence (EL) and photoluminescence (PL) techniques. The radiative recombination intensity was shown to be dependent on the intrinsic material-related parameters such as the doping concentration, growth thickness and the substrate misorientation angle both experimentally and theoretically. The radiative recombination was thus revealed to be an important loss channel of carriers in the GaxIn1-xP/GaAs double-junction tandem solar cells.
Super strong transverse diffusion of minority carriers in the top GaxIn1-xP subcell was found by the micro-EL image surveying. Theoretical simulation on the experimental data shows that the minority carrier diffusion length is as long as ~93 μm at a forward bias of 2.75 V, which is ~30 times longer than that of unbiased GaxIn1-xP epilayer. Origin of this super transverse diffusion was argued, and its influence on device performance was also discussed.
Significant correlations of carrier localization and luminescence behaviors with the substrate misorientation angle in the top GaxIn1-xP subcells were unveiled by excitation intensity- and temperature-dependent PL. The large difference in potential energy profile of GaxIn1-xP layers, caused by the different degrees of atomic ordering, was argued to interpret the observed PL distinctions.
Vertical transport and photoresponse mechanisms of charge carriers in the GaxIn1-xP/GaAs double-junction tandem solar cells were studied by temperature- and reverse bias-dependent photocurrent (PC) spectroscopy. Both the temperature and reverse bias were shown to have significant impact on the device photoresponse, in particular on the photoresponse due to the absorption of photons with energy above the bandgap of GaAs and GaxIn1-xP, namely the supra-bandgap photoresponse. A model was proposed to simulate the observed temperature- and reverse-bias dependence of the supra-bandgap photoresponse.published_or_final_version
Physics
Doctoral
Doctor of Philosophy
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Woods, Michael D. "A comparative analysis of radiation effects on silicon, gallium arsenide, and GaInP2/GaAs/Ge triple junction solar cells using a 30 MeV electron linear accelerator." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion/02Sep%5FWoods.pdf.
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Colin, Clément. "Metallic nano-structures for light-trapping in ultra-thin GaAs and CIGS solar cells." Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-00998396.
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One of the natural tendencies of photovoltaic technologies is the systematic reduction of the thickness of the solar cells in order to reduce the cost, to save rare or toxic elements or to limit recombination. So far, crystalline thin-film (GaAs) and poly-crystalline (CIGS) technology are reaching optimum conversion efficiency for thicknesses around 1 or 2 microns. Typically, this thickness range does not require new solutions of optical trappings as it is the case for amorphous silicon. However, if we want to reduce these thicknesses by a factor of 10 or even 100 to study new concepts of collections and conversions (GaAs or GaSb) or reduce the use of indium (CIGS), new needs for efficient light absorption are necessary for these technologies. This manuscript is focused on the design, simulation and realization of innovative nanophotonic solutions for future ultra-thin crystalline solar cells.As a first step, we were engaged in an approach at odds with the usual design of solar cells to trap light in a ultra-thin (≤100 nm) layer of material (GaAs, GaSb and CIGS). We propose an array of metal nanostructure placed in front of the cell, transferred on a metal mirror in order to obtain a high, multi-resonant absorption independent of the angle of incidence and polarization. Numerical analysis of the resonant mechanisms involved was conducted as well as the fabrication and optical characterization of demonstrators. The results of this study are motivating for future work on the ultra-thin devices, involving new concepts of collection (ballistic transport) or conversion (hot carrier solar cells).On the other hand, we studied the possibility of integrating a rear gold nanostructured back contact (200-400 nm) in thin CIGS solar cells to potentially increase the current of short circuit and open circuit voltage. We have proposed an innovative process to achieve this structure and the optical trapping for CIGS solar cells. Numerical study, manufacture of demonstrators and first measurements are presented.
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SINGULANI, ANDERSON PIRES. "SIMULATION AND DESIGN OF GAAS/ALGAAS QUANTUM WELL SOLAR CELLS AIDED BY GENETIC ALGORITHM." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2009. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=15317@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOA energia é assunto estratégico para a grande maioria dos países e indústrias no mundo. O consumo atual energético é de 138,32 TWh por ano e é previsto um aumento de 44% até o ano de 2030 o que demonstra um mercado em expansão. Porém, a sociedade atual exige soluções energéticas que causem o menor impacto ambiental possível, colocando em dúvida o uso das fontes de energia utilizadas atualmente. O uso da energia solar é uma alternativa para auxiliar no atendimento da futura demanda de energia. O seu principal entrave é o custo de produção de energia ser superior as fontes de energia atuais, principalmente o petróleo. Contudo nos últimos 10 anos foi verificado um crescimento exponencial na quantidade de módulos fotovoltaicos instalados em todo mundo. Nesse trabalho é realizado um estudo sobre célula solares com poços quânticos. O uso de poços quânticos já foi apontado como ferramenta para aumentar a eficiência de células fotovoltaicas. O objetivo é descrever uma metodologia baseada em algoritmos genéticos para projeto e análise desse tipo de dispositivo e estabelecer diretivas para se construir uma célula otimizada utilizando esta tecnologia. Os resultados obtidos estão de acordo com dados experimentais, demonstram a capacidade dos poços quânticos em aumentar a eficiência de uma célula e fornecem uma ferramenta tecnológica que espera-se contribuir para o desenvolvimento do país no setor energético.
The energy is a strategical issue for the great majority of the countries and industries in the world. The current world energy consumption is of 138,32 TWh per year and is foreseen an increase of 44% until the year of 2030 which demonstrates a market in expansion. However, the society demands energy solutions that cause as least ambient impact as possible, putting in doubt the use of the current technologies of power plants. The utilization of solar energy is an alternative to assist in the attendance of the future demand of energy. Its main impediment is the superior cost of energy production in comparison with the current power plants, mainly the oil based ones. However in last the 10 years an exponential growth in the amount of installed photovoltaics modules worldwide was verified. In this work a study on solar cell with quantum wells is carried through. The use of quantum wells already was pointed as tool to increase the efficiency of photovoltaics cells. The objective is to describe a methodology based on genetic algorithms for project and analysis of this type of device and to establish directive to construct an optimized cell using this technology. The results are in accordance with experimental data, that demonstrates the capacity of the quantum wells in increasing the efficiency of a cell and supply a technological tool that expects to contribute for the development of the country in the energy sector.
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Ibaceta, Jaña Josefa Fernanda. "Thermal instabilities of charge carrier transport in solar cells based on GaAs PN Junctions." Tesis, Universidad de Chile, 2017. http://repositorio.uchile.cl/handle/2250/145405.
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Magíster en Ciencias de la Ingeniería, Mención Mecánica.
Ingeniera Civil MecánicaDentro de los factores que afectan negativamente una celda solar fotovoltaica se destaca la temperatura. Ya sea por imperfecciones del material o a condiciones de operación no uniformes, es posible que se concentre calor en una zona debido a la disminución de la resistencia local y su consecuente aumento de corriente eléctrica. Estas zonas de concentración de calor pueden estabilizarse, generando gradualmente degradación de la celda, disminución de su vida útil y eficiencia. En caso contrario, puede ocurrir un fenómeno de descontrol térmico que resulta catastrófico para la celda, inhabilitando su correcto funcionamiento. Estudios en módulos de película delgada revelan que esta condición ocurre incluso cuando la radiación está uniformemente distribuida y con ello, el perfil de temperatura inicial es constante. La evolución temporal, bajo radiación, induce zonas de calor que incrementan exponencialmente la temperatura, contrayendo su área; por otra parte, la temperatura de las zonas más alejadas disminuye simultáneamente mientras disipan pequeñas corrientes. Para evitar este fenómeno se pueden escalar propiedades del dispositivo, como aumentar la conductividad térmica y disminuir el espesor. Actualmente, estos análisis se realizan a partir de modelos numéricos y analíticos basados en el comportamiento de diodos y mediciones experimentales del perfil de temperatura en la capa superficial de la celda y en la juntura. El propósito de esta Tesis es determinar criterios de estabilidad electro-térmico que pueden ser utilizados para evitar el descontrol de temperatura a partir de aplicar un análisis a un modelo hidrodinámico de mayor complejidad que uno basado en diodos; más aún, considerar un estado fuera del equilibro entre la temperatura de la red y los portadores de carga. Se determinó que la inestabilidad ocurre en la juntura PN y depende fuertemente la temperatura de la juntura en los bordes. Además, aumentar la temperatura de los portadores, disminuir el largo y aumentar el voltaje aplicado pueden estabilizar el sistema, aumentando el tiempo en que el sistema duplica su temperatura.
Este trabajo ha sido parcialmente financiado por CONICYT-PCHA/Magíster Nacional/2016 - 22160729
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Lépinau, Romaric de. "GaAs-on-Si solar cells based on nanowire arrays grown by molecular beam epitaxy." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASS090.
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Les nanofils (NF) épitaxiés sur substrat Si sont des absorbeurs optiques efficaces et permettent d’intégrer des matériaux III-V de haute qualité sur Si en évitant les défauts généralement induits par le désaccord de maille entre ces deux matériaux, ce qui permettrait de fabriquer des cellules solaires tandem III-V/Si de plus de 30% d’efficacité. L’objectif de cette thèse est de développer des cellules solaires à NFs III-V, crûes sur substrat Si. Un premier objectif a été le contrôle de la croissance sélective de NFs en réseaux organisés, avec des taux de verticalité reproductibles supérieurs à 90% et atteignant 100%. A partir de caractérisation au microscope électronique en transmission, les conditions de croissance ont été optimisées pour améliorer la qualité cristalline en réduisant le nombre de fautes d’empilement, pour étudier des NFs de GaAsP avec un bandgap optimal, et pour étudier des hétérostructures cœur-coquille. En déterminant la concentration de porteurs dans les NFs par cathodoluminescence, je montre que le dopage du cœur ou de la coquille à un niveau p=8E18 cm⁻³ est possible en utilisant du Be, alors que le dopant Si est amphotère et ne permet d’atteindre que n=5E17 cm⁻³ dans les coquilles. Un procédé de fabrication de cellules a été développé pour contacter des jonctions de NFs cœur-coquille. Un dispositif de première génération basé sur une homojonction GaAs présente une efficacité de 2.1%, limitée par des problèmes de collection des porteurs, alors que la séparation des niveaux de Fermi estimée d'après des mesures de photoluminescence atteint une valeur prometteuse de 0.98 V à 82 soleils, extrapolée à 0.86 V à 1 soleil. Une nouvelle hétérojonction p-i-GaAs/n-GaInP présente une efficacité de 3.7% et un Voc record de 0.65 V. Ces démonstrations de cellules solaires à nanofils ouvrent la voie vers des cellules tandem à haute efficacitéNanowires (NW) epitaxially grown on Si substrate are efficient light absorbers and allow to integrate high-quality III-V materials on Si by preventing defects induced by the lattice-mismatch between both materials. They provide a way to fabricate tandem III-V/Si solar cells above 30% efficiency. The goal of this thesis is to develop III-V NW solar cells grown on Si substrates. First, the control of the selective NW growth in ordered arrays on Si was addressed and vertical yields consistently above 90% and up to 100% were demonstrated. Using transmission electron microscope characterization, the growth conditions were optimized to improve the crystal quality by reducing the number of stacking faults, to investigate GaAsP NWs with the optimal bandgap for tandem, and to study core-shell heterostructures. Using cathodoluminescence to determine the carrier concentrations in NWs, it was shown that the core and the shell can be doped with Be up to p=8E18 cm⁻³, while Si is an amphoteric dopant, resulting in shell doping limited to n=5E17 cm⁻³. A solar cell fabrication process was developed to contact NW core-shell junctions. A first-generation GaAs homojunction device shows efficiencies up to 2.1%, limited by carrier collection issues, whereas the quasi-Fermi level splitting, estimated from PL measurements, reaches a promising value of 0.98 V at 82 sun, extrapolated to 0.86 V at 1 sun. A new core-shell p-i-GaAs/n-GaInP heterojunction exhibits efficiencies up to 3.7%, with a record Voc=0.65 V. These GaAs-based NW top-cells directly grown on Si pave the way toward high-efficiency tandem solar cells
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Moushumy, Nazme A. "Silver (Ag) nanoparticle based masks for the development of antireflection subwavelength structures in GaAs and Si solar cells." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2013. https://ro.ecu.edu.au/theses/862.
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This thesis focuses on the design and development of silver nanoparticles that can be used as masks for the development of antireflection subwavelength grating (SWG) structures. We particularly investigate the impact of silver thin film thickness and the effect of annealing temperature on the fabrication of silver nanoparticles of controlled size and spacing distributions. We also use these measured distributions to predict the performance of subwavelength grating structures developed using dry and isotropic etching of semiconductor substrates.
Silver (Ag) thin films of different thicknesses are deposited on Silicon (Si) and Gallium Arsenide (GaAs) semiconductor substrates and annealed at different temperatures. Uniform nanoparticles with diameters around 200nm and spacing between nanoparticles as low as possible are our target as these parameters are suitable for the fabrication of antireflection SWG structures, having grating widths equal to the nanoparticle diameter and spacing equals to the spacing between nanoparticles. Experimental results demonstrate that by annealing the Ag thin films with different temperature profiles, it is feasible to develop Ag nanoparticles, of diameter around 200nm and spacing below 250nm, at most of the annealing temperatures investigated.
In addition, different subwavelength structures, developed by etching the Ag nanoparticles deposited on Si and GaAs substrates, are simulated using a Finite- Difference Time Domain (FDTD) software package. The simulation results show that substantial reduction in light reflection can be achieved by optimizing the height of the subwavelength structures through the control of the etching time.
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Jain, Nikhil. "Heterogeneous Integration of III-V Multijunction Solar Cells on Si Substrate: Cell Design and Modeling, Epitaxial Growth and Fabrication." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/52045.
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Achieving high efficiency solar cells and concurrently driving down the cell cost has been among the key objectives for photovoltaic researchers to attain a lower levelized cost of energy (LCOE). While the performance of silicon (Si) based solar cells have almost saturated at an efficiency of ~25%, III-V compound semiconductor based solar cells have steadily shown performance improvement at approximately 1% (absolute) increase per year, with a recent record efficiency of 46%. However, the expensive cost has made it challenging for the high efficiency III-V solar cells to compete with the mainstream Si technology. Novel approaches to lower down the cost per watt for III-V solar cells will position them to be among the key contenders in the renewable energy sector. Integration of such high-efficiency III-V multijunction solar cells on significantly cheaper and large area Si substrate has the potential to address the future LCOE roadmaps by unifying the high-efficiency merits of III-V materials with low-cost and abundance of Si. However, the 4% lattice mismatch, thermal mismatch polar-on-nonpolar epitaxy makes the direct growth of GaAs on Si challenging, rendering the metamorphic cell sensitive to dislocations.
The focus of this dissertation is to systematically investigate heterogeneously integrated III-V multijunction solar cells on Si substrate. Utilizing a combination of comprehensive solar cell modeling and experimental techniques, we seek to better understand the material properties and correlate them to improve the device performance, with simulation providing a very valuable feedback loop. Key technical design considerations and optimal performance projections are discussed for integrating metamorphic III-V multijunction solar cells on Si substrates for 1-sun and concentrated photovoltaics. Key factors limiting the “GaAs-on-Si” cell performance are identified, and novel approaches focused on minimizing threading dislocation density are discussed. Finally, we discuss a novel epitaxial growth path utilizing high-quality and thin epitaxial Ge layers directly grown on Si substrate to create virtual “Ge-on-Si” substrate for III-V-on-Si multijunction photovoltaics. With the plummeting price of Si solar cells accompanied with the tremendous headroom available for improving the III-V solar cell efficiencies, the future prospects for successful integration of III-V solar cell technology with Si substrate looks very promising to unlock an era of next generation of high-efficiency and low-cost photovoltaics.Ph. D.
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Barnes, Jennifer M. "An experimental and theoretical study of GaAs/InGaAs quantum well solar cells and carrier escape from quantum wells." Thesis, Imperial College London, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319305.
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Papež, Nikola. "Degradace solárních článků na bázi GaAs." Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2021. http://www.nusl.cz/ntk/nusl-438583.
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Solární články na bázi arsenidu gallia patří mezi nejvýkonější typ dostupných solárních článků vůbec. Jejich výhodou je výborná odolnost vůči tepelnému a ionizujícímu záření, a proto se využívají zejména v náročných podmínkách. Tato disertační práce popisuje stav GaAs fotovoltaických článku vystavených vůči tepelnému namáhání, vysokému ochlazování, gama záření a ozáření širokospektrálním laserem. Vzorky byly zkoumány před, po a i během těchto procesů pomocí několika analytických a charakterizačních metod. Měření bylo zaměřeno na charakterizaci povrchu, optických a elektrických vlastností. Byly objeveny limity a nové chování tohoto typu článků, které jsou ovlivněny i tenkými ochrannými a antireflexními vrstvami.
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Vettori, Marco. "Growth optimization and characterization of regular arrays of GaAs/AIGaAs core/shell nanowires for tandem solar cells on silicon." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEC010/document.
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L'objectif de cette thèse est de réaliser l'intégration monolithique de nanofils (NFs) à base de l’alliage Al0.2Ga0.8As sur des substrats de Si par épitaxie par jets moléculaires via la méthode vapeur-liquide-solide (VLS) auto-assistée et de développer une cellule solaire tandem (TSC) à base de ces NFs.Pour atteindre cet objectif, nous avons tout d'abord étudié la croissance de NFs GaAs, étape clé pour le développement des NFs p-GaAs/p.i.n-Al0.2Ga 0.8As coeur/coquille, qui devraient constituer la cellule supérieure de la TSC. Nous avons montré, en particulier, l'influence de l'angle d'incidence du flux de Ga sur la cinétique de croissance des NFs GaAs. Un modèle théorique et des simulations numériques ont été réalisées pour expliquer ces résultats expérimentaux.Nous avons ensuite utilisé le savoir-faire acquis pour faire croître des NFs p-GaAs/p.i.n-Al0,2Ga0,8As coeur/coquille sur des substrats de Si prêts pour l'emploi. Les caractérisations EBIC réalisées sur ces NFs ont montré qu'ils sont des candidats potentiels pour la réalisation d’une cellule photovoltaïque. Nous avons ensuite fait croître ces NFs sur des substrats de Si patternés afin d'obtenir des réseaux réguliers de ces NFs. Nous avons développé un protocole, basé sur un pré-traitement thermique, qui permet d'obtenir des rendements élevés de NFs verticaux (80-90 %) sur une surface patternée de 0,9 x 0,9 mm2.Enfin, nous avons consacré une partie de notre travail à définir le procédé de fabrication optimal pour la TSC, en concentrant notre attention sur le développement de la jonction tunnel de la TSC, l'encapsulation des NFs et le contact électrique supérieur du réseau de NFsThe objective of this thesis is to achieve monolithical integration of Al0.2Ga0.8As-based nanowires (NWs) on Si substrates by molecular beam epitaxy via the self-assisted vapour-liquid-solid (VLS) method and develop a NWs-based tandem solar cell (TSC).In order to fulfil this purpose, we firstly focused our attention on the growth of GaAs NWs this being a key-step for the development of p-GaAs/p.i.n-Al0.2Ga0.8As core/shell NWs, which are expected to constitute the top cell of the TSC. We have shown, in particular, the influence of the incidence angle of the Ga flux on the GaAs NW growth kinetic. A theoretical model and numerical simulations were performed to explain these experimental results.Subsequently, we employed the skills acquired to grow p-GaAs/p.i.n-Al0.2Ga0.8As core/shell NWs on epi-ready Si substrates. EBIC characterizations performed on these NWs have shown that they are potential building blocks for a photovoltaic cell. We then committed to growing them on patterned Si substrates so as to obtain regular arrays of NWs. We have developed a protocol, based on a thermal pre-treatment, which allows obtaining high vertical yields of such NWs (80-90 %) on patterned Si substrates (on a surface of 0.9 x 0.9 mm2).Finally, we dedicated part of our work to define the optimal fabrication process for the TSC, focusing our attention to the development of the TSC tunnel junction, the NW encapsulation and the top contacting of the NWs
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Baranov, Artem. "Cellules solaires à multijonctions par intégration monolithique de nitrures dilués sur substrats d’arséniure de gallium (GaAs) et de silicium (Si) : études des défauts." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS137/document.
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Les cellules solaires à multi-jonctions de type III-V possèdent des rendements de conversion de l'énergie très élevés (46%). Cependant, les méthodes de fabrication généralement utilisées sont complexes et coûteuses, notamment pour les cellules solaires non monolithiques associées par des techniques de collage et à structure inversée. Cette thèse vise à augmenter les rendements de conversion des cellules solaires monolithiques à l'aide de méthodes prospectives. Le travail est focalisé sur l'étude des défauts électroniquement actifs dans les matériaux constituant les cellules solaires au moyen de techniques photoélectriques et capacitives, et il peut être scindé en trois parties. La première partie traite des cellules solaires à simple jonction avec des couches absorbantes non dopées d'alliages InGaAsN de 1 eV de bande interdite de différentes épaisseurs obtenues sous forme de super-réseaux (InAS / GaAsN) par épitaxie à jets moléculaires (MBE) sur des substrats de GaAs. Pour des épaisseurs inférieures à 1200 nm, la concentration de défauts est négligeable et n'affecte pas fortement les propriétés photoélectriques, tandis que que pour une épaisseur de 1600 nm, la forte concentration de défauts détectés réduit la durée de vie des porteurs photogénérés, et conduit à une baisse significative du rendement quantique externe et des performances de la cellule. La deuxième partie du travail est consacrée à l'étude de cellules solaires à une et plusieurs jonctions avec des couches actives de (In)GaP(As)N obtenues par MBE sur des substrats respectifs de GaP et de Si. Nous avons trouvé que les cellules solaires de type p-i-n avec des couches actives de GaPAsN non dopé présentaient de meilleures performances que les cellules solaires de type p-n avec des couches actives de GaPAsN dopé n. De plus, les cellules solaires avec une couche d'absorbeur en GaPAsN non dopé présentent de meilleures propriétés photoélectriques et des concentrations de défauts plus faibles que celles avec un absorbeur obtenu à partir de super-réseaux InP / GaPN. Plusieurs niveaux de défauts ont été détectés dans la bande interdite de ces matériaux et leurs paramètres ont été décrits en détail. Nous avons montré qu'un traitement de post-croissance approprié pouvait améliorer la qualité électronique des couches et des cellules solaires. Une cellule solaire à triple jonction a été fabriquée avec des couches actives d'absorbeurs de GaPAsN et de GaPN non dopées. La valeur élevée de la tension de circuit ouvert (>2,2V) atteste du fonctionnement des 3 sous-cellules, mais la performance globale est limitée par les faibles épaisseurs de couches d'absorbeurs. Enfin, la troisième partie du travail est consacrée à l'étude de couches de GaP obtenues sur des substrats de Si à des températures inférieures à 400 ° C par une méthode originale de dépôt de couches atomiques assistée par plasma (PE-ALD). En effet, celle-ci utilise un équipement de dépôt chimique en phase vapeur assisté par plasma et elle repose sur l'interaction de la surface avec les atomes de Ga et P provenant respectivement du triméthylgallium et de la phosphine qui sont injectés alternativement. Nous avons également fait croître des couches en utilisant un processus continu (fournissant simultanément les atomes P et Ga) et observé que leurs propriétés électriques et structurelles étaient moins bonnes que celles obtenues par la méthode PE-ALD proposée. Nous avons exploré l'influence des conditions de croissance sur les hétérostructures GaP / Si. Nous avons constaté qu'une faible puissance de plasma RF conduit à de meilleures propriétés photoélectriques, structurelles et à moins de défauts, grâce à une meilleure passivation du substrat de silicium. En outre, nous avons démontré que, contrairement à des résultats de la littérature utilisant des procédés MBE, la technique PE-ALD n'affecte pas ou très peu les propriétés électroniques des substrats de silicium et aucune désactivation des dopants n'a été observéeMulti-junction solar cells based on III-V compounds have reached very high power conversion efficiencies (46%). However, the fabrication methods that are generally used are complex and expensive for non-monolithic bonded and inverted solar cells. This thesis is devoted to the study of prospective methods to increase the efficiency of monolithic solar cells. The work is focused on the study of electronically active defects in the materials constituting the solar cells by means of photoelectric and capacitance techniques (admittance spectroscopy, DLTS,…) and it can be divided into three parts. The first part deals with single-junction solar cells wherein the absorber is made of i-layers of 1 eV bandgap InGaAsN compounds with various thicknesses grown as sub-monolayer digital alloys (SDA) of InAs/GaAsN by molecular-beam epitaxy (MBE) on GaAs wafers. The cell with 900 nm thick InGaAsN exhibits the best photovoltaic performance and no defects could be evidenced from capacitance techniques. When the thickness is increased to 1200 nm, defects were detected, but their concentration is low so it did not strongly affect the photoelectric properties. Further increase to 1600 nm of the layer thickness was shown to lead to a higher defect concentration causing a change in the band diagram of the structure and lowering the lifetime of photogenerated carriers. This could explain the drastic drop of the external quantum efficiency, and the overall poor performance of the solar cell. The second part is devoted to the study of single- and multi-junction solar cells with active layers of (In)GaP(As)N grown by molecular beam epitaxy (MBE) on GaP and Si wafers, respectively. More precisely, the active layers were either quaternary alloys of GaPAsN or SDAs of InP/GaPN. We found that p-i-n type solar cells with active layers of i-GaPAsN showed better performance than p-n type solar cells with active layers of n-GaPAsN due to higher EQE values. Moreover, solar cells with an i-GaPAsN absorber layer show better photoelectric properties and lower defect concentrations, than those with an SDA InP/GaPN absorber layer. Different defect levels were detected by capacitance methods in these materials and their parameters were described in detail. We showed that a suitable post-growth treatment could improve the electronic quality of the GaPAsN layer and the solar cell properties. Also, a triple-junction solar cell was fabricated with active layers of i-GaPAsN and i-GaPN. All subcells were found to be operating, leading to a large open circuit voltage (>2.2 V), but the overall performance is limited by the low value of the quantum efficiency due to low thicknesses of i-layers that should be increased for better absorption. Finally, the third part is devoted to the study of GaP layers grown on Si wafers at temperatures below 400 °C using an original method called plasma-enhanced atomic-layer deposition (PE-ALD). Indeed, it uses a plasma-enhanced chemical vapor deposition equipment and it is based on the alternate interaction of the wafer surface with Ga and P atoms coming from injected trimethylgallium and phosphine, respectively. We also grew layers using a continuous process (providing simultaneously the P and Ga atoms) and observed that their electric and structural properties were poorer than that grown by the proposed PE-ALD method. The influence of growth conditions on the GaP/Si heterostructures was explored. We found that low RF-plasma power leads to better photoelectric, structural and defect-related properties, due to a better passivation of the silicon wafer. In addition, we demonstrated that, contrary to results reported in the literature using MBE processes, our growth process does not affect the electronic properties of phosphorous doped n-Si wafers, while slight changes were observed in boron-doped p-Si wafers containing Fe-related defects, however without deactivation of the doping nor strong degradation of the electronic properties
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Koroliov, Anton. "Semiconductor characterization by terahertz radiation pulses." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2014. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2014~D_20140922_141151-18493.
Full textAbstract:
The goal of this dissertation work was to develop pulsed terahertz radiation techniques and use them to study different properties of the semiconductor materials and semiconductor devices. Three groups of materials were investigated: GaAsBi, GaAs nanowires, copper-indium chalcogenide. The used techniques are THz-TDS, optical pump – THZ probe, optical pump – optical probe and THz excitation spectral measurements. The main results that were presented in this dissertation are the following: thermal annealing has resulted in the shortening of electron lifetime in GaAsBi to picosecond values, which is important achievement for the application of this material in THz range components. In GaAsBi layers with larger than 10% Bi content absorption bleaching recovering on the picosecond time scale and its saturation can be realized when the wavelengths of the optical signals are as long as 1600 nm. The results of these studies can be applied in the production of SESAM with bismide absorption layer. The samples with GaAs nanowires emit THz radiation several times better than the bulk GaAs substrates due to enhanced light absorption because of localized surface plasmon resonances in GaAs nanowires. THz emission efficiency from thin copper-indium chalcogenide layers strongly depends on their stoichiometry and on the parameters of the top transparent contact layers, thus it can be used for the mapping of built-in electric fields in solar cells made from these layers.Šio darbo tikslas buvo susipažinti su terahercinių impulsų generavimo ir detektavimo būdais, įsisavinti įvairias terahercinių impulsų panaudojimo metodikas bei pritaikyti jas puslaidininkių medžiagų ir puslaidininkinių prietaisų tyrimui. Buvo tirtos trys medžiagų grupės: GaAsBi, GaAs nanovielutės ir Cu – In chalkogenidai. Tyrimui buvo naudojamos: THz – TDS, optinio žadinimo – THz zondavimo, optinio žadinimo – optinio zondavimo bei THz sužadinimo spektroskopijos metodikos. Pagrindiniai rezultatai aprašyti disertacijoje yra šie: GaAsBi bandinių atkaitinimas stipriai sumažino krūvininkų gyvavimo trukmes, kas yra naudinga THz komponentų gamyboj. Optinio praskaidrėjimo efektas ir pikosekundžių eilės krūvininkų gyvavimo trukmės GaAsBi epitaksiniuose sluoksniuose su 10% ir daugiau Bi atomų stebimas žadinant juos optine spinduliuote, kurios bangos ilgiai siekia iki 1600 nm. Šios GaAsBi bandinių savybės leidžia juos priakyti įsisotinančių sugėriklių veidrodžių gamyboje. Bandiniai su GaAs nanovielutėmis emituoja THz spinduliuotę kelis kartus geriau nei GaAs padėklas, dėl padidėjusios sugerties, kurią skatina paviršinių optinių plazmonų rezonansai GaAs nanovielutėse. THz emisijos efektyvumas iš Cu-In chalkogenidų sluoksnių stipriai priklauso nuo jų stechiometrijos ir viršutinio skaidraus kontakto parametrų, ir gali būti naudojamas saulės elementų, pagamintų šių sluoksnių pagrindu, vidinių elektrinių laukų tyrimui.
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Koroliov, Anton. "Puslaidininkių charakterizavimas terahercinės spinduliuotės impulsais." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2014. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2014~D_20140922_141205-51499.
Full textAbstract:
Šio darbo tikslas buvo susipažinti su terahercinių impulsų generavimo ir detektavimo būdais, įsisavinti įvairias terahercinių impulsų panaudojimo metodikas bei pritaikyti jas puslaidininkių medžiagų ir puslaidininkinių prietaisų tyrimui. Buvo tirtos trys medžiagų grupės: GaAsBi, GaAs nanovielutės ir Cu – In chalkogenidai. Tyrimui buvo naudojamos: THz – TDS, optinio žadinimo – THz zondavimo, optinio žadinimo – optinio zondavimo bei THz sužadinimo spektroskopijos metodikos. Pagrindiniai rezultatai aprašyti disertacijoje yra šie: GaAsBi bandinių atkaitinimas stipriai sumažino krūvininkų gyvavimo trukmes, kas yra naudinga THz komponentų gamyboj. Optinio praskaidrėjimo efektas ir pikosekundžių eilės krūvininkų gyvavimo trukmės GaAsBi epitaksiniuose sluoksniuose su 10% ir daugiau Bi atomų stebimas žadinant juos optine spinduliuote, kurios bangos ilgiai siekia iki 1600 nm. Šios GaAsBi bandinių savybės leidžia juos priakyti įsisotinančių sugėriklių veidrodžių gamyboje. Bandiniai su GaAs nanovielutėmis emituoja THz spinduliuotę kelis kartus geriau nei GaAs padėklas, dėl padidėjusios sugerties, kurią skatina paviršinių optinių plazmonų rezonansai GaAs nanovielutėse. THz emisijos efektyvumas iš Cu-In chalkogenidų sluoksnių stipriai priklauso nuo jų stechiometrijos ir viršutinio skaidraus kontakto parametrų, ir gali būti naudojamas saulės elementų, pagamintų šių sluoksnių pagrindu, vidinių elektrinių laukų tyrimui.The goal of this dissertation work was to develop pulsed terahertz radiation techniques and use them to study different properties of the semiconductor materials and semiconductor devices. Three groups of materials were investigated: GaAsBi, GaAs nanowires, copper-indium chalcogenide. The used techniques are THz-TDS, optical pump – THZ probe, optical pump – optical probe and THz excitation spectral measurements. The main results that were presented in this dissertation are the following: thermal annealing has resulted in the shortening of electron lifetime in GaAsBi to picosecond values, which is important achievement for the application of this material in THz range components. In GaAsBi layers with larger than 10% Bi content absorption bleaching recovering on the picosecond time scale and its saturation can be realized when the wavelengths of the optical signals are as long as 1600 nm. The results of these studies can be applied in the production of SESAM with bismide absorption layer. The samples with GaAs nanowires emit THz radiation several times better than the bulk GaAs substrates due to enhanced light absorption because of localized surface plasmon resonances in GaAs nanowires. THz emission efficiency from thin copper-indium chalcogenide layers strongly depends on their stoichiometry and on the parameters of the top transparent contact layers, thus it can be used for the mapping of built-in electric fields in solar cells made from these layers.
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Koletsios, Evangelos. "GaAs/InAs multi quantum well solar cell." Thesis, Monterey, California. Naval Postgraduate School, 2012. http://hdl.handle.net/10945/27856.
Full textAbstract:
In this thesis, Silvaco software is used to form a precise, well-controlled reliable, and inexpensive solar-cell structure using quantum wells. Successful results will allow the exploitation of most of the advantages of quantum-well systems. This challenging research represents the first time that Silvaco simulation software has been used in the design of such a solar cell. This research field is promising because of the potential to increase the attainable energy efficiency of solar photon conversion, due to tunable bandgaps, which can absorb most of the solar spectrum, which conventional single-layer crystalline solar cells cannot do. The ultimate goal is the assembly of a quantum-well layer. A theoretical infinite-layer cell can reach an efficiency of 86% (constrained by thermodynamical limits). Quantum wells can reach 65%+ when a multilayer cell has reached 49%, and it is very expensive to build.
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Andre, Carrie L. "III-V semiconductors on SiGe substrates for multi-junction photovoltaics." The Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=osu1100290985.
Full text
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Yang, Cheng-Yu, and 楊正宇. "ZnSeO/GaAs Solar Cells." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/44077735985013342517.
Full textAbstract:
碩士國立中央大學
電機工程研究所
100
To date, materials with intermediate band become potential applications in solar cells because the spectral response could be extended by the intermediate band in the forbidden gap. In this thesis, we first demonstrated the ZnSeO based intermediate band solar cells and its characteristics were particularly investigated. The structural and optical properties of ZnSeO with varying oxygen content were studied in this work. The high absorption coefficients (>104 cm-1) of ZnSeO made it a promising candidate in solar cell. Theoretical calculation based on self-consistent drift-diffusion method was referred in this work. The results showed the conversion efficiency of ZnSeO based solar cell could reach 25 %. To realize the solar cell structure, ZnSeO with n-ZnO window layer were grown on p-GaAs substrate in this study. We also propose Ti/Al/Ni/Au ohmic contact to minimize the series resistance and power consume in solar cells, and low specific contact resistivity of 2.6×10-7 Ω-cm2 could be achieved. The ZnSeO based solar cells exhibit a 16 % increase of the short circuit current and same open circuit voltage in comparison to ZnSe based cells. Thus, a 43 % improvement in conversion efficiency could be obtained. However, existence of intermediate band could not be observed in ZnSeO solar cell because of the quality issues. This work does provide the opportunities for ZnSeO applied in photovoltaic devices.
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Lin, Yan-Zhang, and 林彥璋. "Simulation of GaAs solar cells in nanoscale." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/47zcn2.
Full textAbstract:
碩士國立交通大學
光電系統研究所
106
We simulate both of optical and electrical modules into GaAs nanorod solar cell with SiO2 side-contact as the passivation of sidewall. In optical simulation, consider the height and thickness of SiO2 layer. Absorption, reflection and transmission were observed to know the influence of the SiO2 side-contact layer in the optical characteristic. Among this, also compute the total generation profile in nanorod which we assume as the interpolation of the generation rate into electrical simulation. In electrical simulation, study the height and thickness dependence of SiO2 contact layer. The all contact (top, side and bottom contact) are assumed as ideal contact which can ignore the relative resistance between metal and semiconductor connected. Under the set up above, SiO2 layer can enhance the current-voltage characteristic to higher Jsc. At short height of SiO2, the enhancement is probably unstable that Jsc moves up and down. while at tall height of SiO2 layer, the influence of passivation layer becomes lower that lead Jsc beginning decrease. In thickness dependence, the layer must be thick enough to obtain better performance efficiently. Since the nanorod solar cells have larger surface-to-volume ratio, surface recombination is an important factor which heavily influence the performance of nanoscale solar cells.
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Huang, Pei-Hsuan, and 黃珮瑄. "Optimum design of GaAs triple-junction solar cells." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/01872114017613334045.
Full textAbstract:
碩士元智大學
光電工程研究所
99
In this research, we study the efficiency enhancement in III-V compound semiconductor solar cell. In the first section of my thesis, we study the InGaP single junction solar cell with sub-wavelength surface texture structures by rigorous coupled wave analysis. The simulation of optimal structure result of the reflectance will be taken into APSYS software. The enhancement of the current density and efficiency were 2.39 % and 3.55 %, respectively. In the second section of my thesis, we present three processes to enhance the InGaP/GaAs/Ge triple junction solar cell efficiency. First, optimal the thickness of main absorption layer. The enhancement of the current density and efficiency were 9.29 % and 5.62 %, respectively. Second, optimum design of InGaP/GaAs/Ge triple-junction solar cells with sub-wavelength surface texture. The enhancement of the current density and efficiency were 6.90 % and 7.27 %, respectively. Third, combination optimal the thickness of main absorption layer with optimal sub-wavelength surface texture structure. The enhancement of the current density and efficiency were 16.27 % and 12.99 %, respectively.
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Lee, Yueh-Mu, and 李岳穆. "Fabrication of GaAs Solar Cells on Silicon Substrates." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/73615424291525196364.
Full textAbstract:
碩士大葉大學
電機工程學系
95
Compared with silicon solar cell, single junction GaAs and multi-junction InGaP/GaAs solar cell grown on single-crystal GaAs substrates have achieved record efficiency of 25.7％ and 29.5％, respectively, under AM1.5 illumination. 40% of efficiency has been achieved on InGaP/GaAs/Ge triple-junction solar cells. Even so, a signification cost reduction is needed for application of these solar cells to terrestrial photovoltaic systems. The cost for the manufacture of GaAs based solar cell can be attributed to the usage of single-crystal GaAs or Ge substrates and the utilization of epitaxy technology. In the thesis, a cheap material, silicon, was adopted as substrates. In order to use Si substrates for the growth of GaAs solar cells, an amorphous Ge film was deposited on Si substrate surface. Then, the amorphous Ge film was re-crystallized by a thermal annealing process. Finally, GaAs solar cell structure was grown on the poly-crystalline Ge film/Si substrates.
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BAI, WEN-BIN, and 白文賓. "Performance enhancement of single-junction GaAs solar cells." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/8544hv.
Full textAbstract:
碩士國立臺北科技大學
光電工程系
106
In this study, the conversion efficiency of single-junction GaAs solar cells using (a) double layer (ITO/SiO2) anti-reflection and (b) metal/oxide/semiconductor (MOS) structure deposited by thermally RF-sputter were proposed and demonstrated. Optical reflectance, external quantum efficiency, dark current-voltage, and photovoltaic current-voltage of are measured and compared. Type-(a): The optical reflectance of double layer anti-reflection was simulated using TFCalcTM optical thin film software to show a low reflective spectrum at the GaAs solar cells. That in the GaAs solar cells with ITO (41 nm) and SiO2 (58 nm) double-layer anti-reflection layer exhibited the best short circuit current density enhancement, its short circuit current density enhancement (ΔJsc) of 28.43% (from 22.19 mA/cm2 to 28.50 mA/cm2) and conversion efficiency enhancement (Δη) of 30.35% (from 18.78% to 24.48%) were obtained. Type-(b): GaAs solar cells are fabricated using metal-oxide/semiconductor (MOS) structures using Al2O3 or TiO2 as a oxide films, Applying various voltages on the ITO electrode to enhance photovoltaic performance was observed, For the a case of MOS-structure cell, Al2O3/ITO, the short-circuit current density enhancement (ΔJsc) of 15.25% (from 22.69 mA/cm2 to 26.15 mA/cm2) and conversion efficiency enhancement (Δη) of 13.35% (from 18.28% to 20.72%) were obtained; and the oxide layer was TiO2 sputtered ITO transparent electrode (TiO2/ITO), the short-circuit current density enhancement (ΔJsc) of 21.09%(from 23.14 mA/cm2 to 28.02 mA/cm2) and conversion efficiency enhancement (Δη) of 22.40% (from 18.75% to 22.95%) were obtained. To study the biase effection MOS GaAs solar cell, the cell biased at -3.6 V, Jsc of 34.43 mA/cm2, and η of 26.50% foe the cell with Al2O3/ITO were obtained. Similarly, the cell with TiO2/ITO and biased at -3.6 V, Jsc of 36.64 mA/cm2 and η of 28.07% were obtained.
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Lin, Y. C., and 林裕鈞. "Process Study for the Fabrication of GaAs Solar Cells." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/13332939975570695625.
Full textAbstract:
碩士大葉大學
電機工程學系
96
Heavily doped n+-GaAs material plays important role in optoelectronics for the formation of ohmic contacts. Gold always is the popular metal for the electrode formation in the fabrication of optoelectronic devices. Regarding to solar cells, about 10% of cell area is covered with metal electrodes. In order to reduce the fabrication cost, cheaper metals shall be adopted for the formation of metal electrodes on solar cells. In this work, three kinds of metal combination, including Ni/Ag/Au, Ni/Al/Au, and Ni/Cu/Au, were deposited on n+-type GaAs to form non-alloyed ohmic contacts and be characterized, respectively. All samples were thermal treated with various different temperatures and times to evaluate the thermal stability. The characteristic contact resistances (ρc) were characterized by transmission line model (TLM). The inter-diffusions between metal and semiconductor after thermal treatment were characterized by X-ray diffractometer (XRD).
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"High Efficiency GaAs-based Solar Cells Simulation and Fabrication." Master's thesis, 2014. http://hdl.handle.net/2286/R.I.24949.
Full textAbstract:
abstract: GaAs-based solar cells have attracted much interest because of their high conversion efficiencies of ~28% under one sun illumination. The main carrier recombination mechanisms in the GaAs-based solar cells are surface recombination, radiative recombination and non-radiative recombination. Photon recycling reduces the effect of radiative recombination and is an approach to obtain the device performance described by detailed balance theory. The photon recycling model has been developed and was applied to investigate the loss mechanisms in the state-of-the-art GaAs-based solar cell structures using PC1D software. A standard fabrication process of the GaAs-based solar cells is as follows: wafer preparation, individual cell isolation by mesa, n- and p-type metallization, rapid thermal annealing (RTA), cap layer etching, and anti-reflection coating (ARC). The growth rate for GaAs-based materials is one of critical factors to determine the cost for the growth of GaAs-based solar cells. The cost for fabricating GaAs-based solar cells can be reduced if the growth rate is increased without degrading the crystalline quality. The solar cell wafers grown at different growth rates of 14 μm/hour and 55 μm/hour were discussed in this work. The structural properties of the wafers were characterized by X-ray diffraction (XRD) to identify the crystalline quality, and then the as-grown wafers were fabricated into solar cell devices under the same process conditions. The optical and electrical properties such as surface reflection, external quantum efficiency (EQE), dark I-V, Suns-Voc, and illuminated I-V under one sun using a solar simulator were measured to compare the performances of the solar cells with different growth rates. Some simulations in PC1D have been demonstrated to investigate the reasons of the different device performances between fast growth and slow growth structures. A further analysis of the minority carrier lifetime is needed to investigate into the difference in device performances.Dissertation/Thesis
M.S. Electrical Engineering 2014
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Chen, Li Wei, and 陳勵瑋. "Fabrication of Inverted GaAs Solar Cells on Silicon Substrates." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/99155898985047153281.
Full textAbstract:
碩士大葉大學
電機工程學系
98
This study is to investigate the fabrication of inverted GaAs solar cells on silicon substrates by wafer bonding and epitaxial lift-off technique. Conventional InGaP/GaAs/Ge-based triple junction solar cells with high conversion efficiency have been demonstrated. However, Ge junction contributes only 270 mV to open circuit voltage due to 0.66 eV of bandgap energy for Ge. By switching to InGaAs, the bandgap energy of this junction increases to 1.03 eV. Typical voltages of 550~650 mV can be generated, which enables it to be joined to InGaP/GaAs junctions without limiting the cell’s current. This approach involves growing InGaP and GaAs junctions that are lattice matched to a Ge or GaAs substrate in an inverted manner. Any dislocations are then confined to the InGaAs junction, which is deposited on top of the InGaP/GaAs dual junctions. Moreover, GaAs substrates removed by epitaxial lift-off technique are recyclable to save resource and prevent form waste. In this study, wafer bonding technique was applied to connect inverted GaAs solar cells and Si substrates by Au/Ag/Au and Au/Sn/Au. Then GaAs substrates were separated from inverted GaAs solar cells by epitaxial lift-off technique. Finally, the fabrication of inverted GaAs solar cells without any antireflection coating (ARC) was finished by photolithography. The measured open circuit voltage (Voc), short circuit current density (Jsc), fill factor (F.F.) and conversion efficiency (η) of the thin film GaAs solar cells on silicon substrates were 0.85V, 20.58mA/cm2, 0.74 and 12.8% respectively.
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Cheng, Chieh-wen, and 鄭傑文. "Wafer-bonded PEDOT:PSS/GaAs thin-film hybrid solar cells and Wafer-scale PEDOT:PSS/Si hybrid solar cells." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/90953425913119300561.
Full textAbstract:
碩士國立交通大學
應用化學系碩博士班
104
In recent years, development of hybrid solar cells which combines the advantages from inorganic materials and organic solar cells provides a simple, low temperature process to fabricate solar cell devices with reduced cost. Content of this thesis work was divided into two parts. In the first part, we demonstrated a PEDOT:PSS on GaAs thin film hybrid solar cells by using wafer bonding and chemical wet etching techniques. The thin film hybrid solar cells reached an excellent power conversion efficiency efficiency of 8.93% when an additional p+ Al0.3Ga0.7As epi-layer is deposited on the surface of the solar cells to provide a front-surface field. However, we uncovered that the bonding materials was able to diffuse into the GaAs thin film during the wafer-bonding stage, which led to the decrease in efficiency. In the second part of the thesis, we demonstrated an 4 inch PEDOT:PSS/silicon hybrid solar cell device by adding the DuPont Capstone FS-31 surfactant into the spin-coated PEDOT:PSS layer. Effects of the non-uniformity of the PEDOT:PSS layer on cell performance was investigated. The device achieved an overall conversion efficiency of 10.25% and a total output current and voltage of 26.23 mA/cm2 and 0.46 V, respectively. The as-made large-area solar cells benefits from the reduction in the fabrication time and cost, and particularly in preventing the pollution from the wafer-cutting.
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Wu, Po-Ching, and 吳柏慶. "Optical and electrical simulations of GaAs nanorod array solar cells." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/c84yxa.
Full textAbstract:
碩士國立交通大學
光電系統研究所
105
There have been many theoretical analyses and simulations about the anti-reflection and light-trapping properties of nanorod array solar cells, as well as the unique radial junction design. However, in continuity equations of electrical simulations, generation term of nanorod solar cells used to be approximated by Beer Lambert law same as the planar counterpart. In this work, we build the optical and electrical models of GaAs nanorod array solar cells by radio frequency and semiconductor module on COMSOL Multiphysics® software, and present the coupled optical and electrical results. In optical simulations, optimal nanorod array arrangement was obtained through light scattering and photocurrent analyses. In electrical simulations, doping and junction design were optimized through studies of current-voltage characteristics and electric field distributions. In addition, due to the high surface-to-volume ratio, surface defects and high surface states of III-V semiconductor interface would largely influence solar cells’ performances. We performed the numerical study on the influence of surface recombination velocity and interface barrier height. Finally, according to our simulation results, GaAs nanorod array solar cells can achieve 20% power conversion efficiency with good sidewall passivation.
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Lee, Chyi-Lin, and 李奇霖. "Fabrication and Simulation Anaylsis of High Efficiency GaAs Solar Cells." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/13193936277442977376.
Full textAbstract:
碩士國立交通大學
電子物理學系
84
High efficiency solar cells can be applied on space satellites and power plants. GaAs solar cells is a good choice forhigh efficiency solar cell. In this research we will discuss thefabrication and theory simulation analysis of high- efficiency GaAssolar cells. In this research the method of image reversal is usedto produce the top contact of GaAs solar cells. Because of the image reversal technique, the width of fingers can be reduced from 400 ?m to 20 ?m. So the lateral resistance can be reduced and the fill factor will be improved. In this article we use the low-high junction model to analyze the GaAs solar cell. From the simulation how the structure parameter affect the solar cells preformance can be understood. So wecan use this result to design our solar cells. Moreover a spectral response system is established. From this system the quantum efficiency for all solar cell components can be investigated. We also successfully demonstrate a 15.6% GaAs solar cell.This efficiency is measured under AM1, one sun and without AR coating.We expect that if AR coating is used on the solar cell, the efficiency will increase by 2~3% and reach about 18%.
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Tseng, Chun-Yen, and 曾俊硯. "Performance Improvement of GaAs Solar Cells Using Photoelectrochemical Oxidation Method." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/54392231118945623884.
Full textAbstract:
碩士國立成功大學
光電科學與工程研究所
97
The purpose of this research is to investigate the passivation mechanism of the window layer (AlGaAs) of GaAs solar cell by using photoelectrochemical oxidation method (PEC). The advantage of this passivation method is using its self-oxidation material to reduce the energy loss from the surface states on the window layer. The conversion efficiency of the GaAs solar cell with and without photoelectrochemical oxide treatment would be investigated. The conversion efficiency can be improved due to the reduction of surface state densities. Furthermore, in order to reduce the losses from the solar reflection, double anti-reflection coating was fabricated by electron-beam deposition system. In our research, the conversion efficiency was improved to 15.7% by using the photoelectrochemical oxidation method.
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Sheng, Jhih-Syuan, and 盛致璿. "Study of Solar Cells Based on Ge and GaAs Materials." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/46845895572262126050.
Full textAbstract:
碩士高雄師範大學
物理學系
98
Study of Solar Cells Based on Ge and GaAs Materials Jhih-Syuan Sheng* Jung-Hui Tsai** Department of Physics, National Kaohsiung Normal University, Kaohsiung, Taiwan, R.O.C Abstract In this thesis, we simulated and analyze two kinds of homojunction solar cells based on Ge and GaAs materials by the SILVACO simulation program. First, we consider the characteristics of Ge homojunction solar cells with different emitter concentrations. η increases from 5.48 % to 8.64 % when the concentration is increased from 2 x 1016 to 2 x 1019 cm-3 and become saturated at 9.26 % as the concentration is larger than that of 2 x 1021 cm-3. Another, as seen from the relationship between conversion efficiency η and emitter thickness, η increase form 7.86% to 9.28% when the emitter thickness is increased from 200 to 15000 Å. In chapter 3, we analyze the characteristics of GaAs homojunction solar cells with different emitter concentrations. η value decreases from 15.01 % to 8.91 % as the concentration is increased from 2 x 1018 to 2 x 1022 cm-3. It is clear that Isc decreases with increasing emitter doping concentration and minority carrier lifetime becomes shorter, lead to η decreases quickly. On the other hand, for considering the effect of emitter thickness for GaAs solar cells, the conversion efficiency decreases form 15.05 % to 8.58 % as emitter thickness is increased from 500 to 15000 Å. This result can be attributed that the relatively small diffusion length of minority carriers in GaAs layers, resulting in the large amount of recombination in neutral-emitter region. * Author ** Advisor
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Tsai, Jia-Ling, and 蔡佳霖. "Optimized Design of Back-Contact Thin-Film GaAs Solar Cells." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/vn8ukq.
Full textAbstract:
碩士國立交通大學
光電工程研究所
106
In recent years, breakthroughs of silicon-based solar cells adopt the concepts of back contacts and back junction. The design not only eliminates the shadowing caused by the front contact but also decreases the series resistance. If such a design is applied to GaAs, the material with the highest single-junction power conversion efficiency (PCE)[1, 2], it may be possible to enhance the power conversion efficiency further. However, only few experiments on back-contact GaAs solar cells have been conducted due to fabrication challenges. In this work, we aim to optimize the design parameters by employing a validated Sentaurus TCAD model, including the doping concentration, base thickness, length and pitch of back electrodes. Through current-voltage characteristics, we could determine the best cell performance with different material qualities and their correlation to design parameters. Our study shows that the optimized thickness and doping concentration of back-contact solar cells correspond to 1.4 ~1.7 um and 5×〖10〗^16 cm^(-3) for all material qualities. Compared to conventional GaAs solar cells, the back-contact device have a relatively short diffusion length and large dark current, but PCE is 1~2% higher due to the increment of short-circuit current. Moreover, we show that while the optical shadowing is eliminated in the back-contact design, the electrical shading still affects the cell performance and is sensitive to the electrode length and pitch. Consequently, our simulation shows that both the anode and pitch should be relatively narrow in order to mitigate the recombination loss above the anode region.
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Wu, Chung-Hsien, and 吳崇賢. "Performance Investigation of Sub-Cells in InGaP/GaAs/Ge Triple-Junction Solar Cells." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/23276504555536741375.
Full textAbstract:
碩士國立臺灣海洋大學
電機工程學系
96
In this thesis, we demonstrate that a novel triple-junction solar cell structure, using the materials of Ge, GaAs and InGaP from bottom to top, simultaneously obtains three sets of pn junction to form the three sub-solar-cell with series shunt. In addition, the model of energy conversion efficiency has also been presented. According to tune the open circuit voltage and short circuit current every sub-solar-cell to find out the influence of output characteristics and the suitable operation point, we successfully solved the current mismatch owing to three sub-solar-cell with series shunt. We obtained the excellent energy conversion efficiency. This way is the Non-Destructive measurement.
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張仕添. "Numerical Study on InGaP/GaAs Dual-Junction and InGaP/GaAs/InGaAs Triple-Junction Solar Cells." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/81234859975370333229.
Full textAbstract:
碩士國立彰化師範大學
光電科技研究所
97
ABSTRACT Being a green energy source, the development of solar cell technology has continuous advancement in recent years. The series-connected multi-junction solar cells based on the III-V semiconductor material system are proven to be attractive for many space and terrestrial applications in substituting for the conventional solar cells based on silicon. In this thesis, the properties of InGaP/GaAs dual-junction and InGaP/GaAs/InGaAs triple-junction solar cells are investigated numerically by using the APSYS simulation program. In order to markedly increase the sunlight-to-energy conversion efficiency, the thickness of each cell is modified to gain the matched short-circuit current. In chapter 1, the material properties and the development history of the solar cells are introduced. In chapter 2, the device physics of solar cells and the relevant physical parameters used in the APSYS software are mentioned. In chapter 3, based on an experimental InGaP/GaAs dual-junction solar cell, the concept of current matching is studied. By changing the layer thickness of the top cell, the photon current and conversion efficiency can be improved by current matching. Under the situation of AM0 and one sun, when the thickness of the top cell base layer changes from 0.55 µm to 0.4 µm, the conversion efficiency is improved by 3%. In chapter 4, the current matching for the InGaP/GaAs/InGaAs triple-junction solar cell is then investigated. By optimizing the layer thickness of the top and middle cells, the appropriate solar cell structure which possesses high sunlight-to-energy conversion efficiency is recommended. Under the situation of AM1.5G and one sun, when the base layer thicknesses of the top cell and middle layer are 0.4 μm and 1.5 μm, respectively, the photon current is matched and the conversion efficiency is improved by 2.3%. Under the situation of AM0 and one sun, when the base layer thicknesses of the top cell and middle layer are 0.3 μm and 1.7 μm, respectively, the conversion efficiency is improved by 4.2%. At AM1.5D and one sun, when the base layer thicknesses of the top cell and middle layer are 0.5 μm and 1.7 μm, respectively, the conversion efficiency is improved by 1.3%. Finally, a summary to the previous studies is provided in chapter 5.
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Lin, Yu-Cheng, and 林昱成. "The Process Study of Back-Contact GaAs Thin-Film Solar Cells." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/39737447755528377283.
Full textAbstract:
碩士中原大學
電子工程研究所
104
For single junction solar cell, GaAs is an excellent material due to its material properties such as direct bandgap can effectively absorbing and emitting light, good radiation hardness and low temperature coefficient make GaAs solar cells extensively used for space applications and concentrated photovoltaic systems. Single-junction GaAs solar cells can be as high as 33.5% under AM1.5G illumination in theory. The high efficiency back-contact silicon solar cells have been extensively explored, and many designs of back-contact type have been suggested during the last 40 years. Cells can achieve potentially higher efficiency by moving all or part of the frontside electrodes to the rear of the device to eliminate shading losses. Whether silicon solar cells were made in the conventional type or in back-contacted structure, it always needs hundreds micrometers of active layers to absorb the visible light due to its indirect bandgap and lower absorption coefficient. Compared with silicon, GaAs solar cells can absorb 99% light in the few micrometers is more suitable for thin-film devices and back-contacted design. In this study, we started to numerically simulate the performance of back-contact GaAs solar cells by using our in-house developed program, and use the results to design the epitaxial structure and process flow, then we combine the epitaxial lift-off technique to transfer the GaAs epilayer from the GaAs substrate to the flexible substrate to realize a lightweight and flexible thin-film solar cells. And we measure the current-voltage characteristics and quantum efficiency to confirm the performance of solar cells, under AM1.5G illumination, the conversion efficiency can achieve 20.904% and current density is 25.420mA/cm2. After optimization the p-electrode spacing and the anti-reflection coating, the conversion efficiency is 21.104% and current density is 25.732 mA/cm2 . This approach brings the potential of back-contacted design to thin-film solar cells. With further investigation and optimization on this structure and combine GaAs substrate re-use process to achieve a low-cost, high-efficiency thin-film solar cell.
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Li, Chia-Hao, and 黎家豪. "Study on Thin Film GaAs Solar Cells and Substrate Reused Technologies." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/9aqnkw.
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碩士國立中興大學
精密工程學系所
99
This thesis focuses on fabrication of thin-film solar cell via cross-shaped pattern epitaxial lift-off (CPELO) technology. The device performance of different recycled times thin-film GaAs solar cell will be discussed and compared. The cross-shaped pattern array is used to define cell size and provide the etch path of etchant solution. The AlAs sacrificial layer is etched by hydrofluoric acid etchant through the cross-shaped hole. The CPELO technique does not require a temporary carrier substrate to transfer the epilayers because the desired carrier substrate is directly deposited onto the backside of epilayers before the epitaxial lift-off process. The desired carrier, the electroplate nickel substrate, can be contacted directly to the epilayer without wax or low-viscosity epoxy. The release time of the 2-inch wafer with 1mm2 cell sizes is about 2 hours. After CPELO process, the separated GaAs substrate can be recycled via chemical cleaning. The substrate degradation after lift-off was investigated using atomic force microscopy (AFM). The surface roughness is about 0.30 nm for new wafers and 0.50nm, 1.36nm after first and second substrate reused. With the increased roughness, the thin-film solar cell reduced in open-circuit voltage (Voc) in one-sun AM 1.5G light source. The Voc of thin-film cell separated from new GaAs substrate is 0.95 V. Compared to thin-film cells separated from first and second recycled GaAs substrate are 0.76 V and 0.66 V, respectively. Reused GaAs substrate surface roughness will lead to reduce the quality of epitaxy layer and also deteriorate the thin-film cell efficiency.
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Su, Yu-Chih, and 蘇裕智. "Characteristics of Thin-Film GaAs Solar Cells with Optical Selective Filter." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/13776929558884419797.
Full textAbstract:
碩士國立交通大學
光電工程研究所
104
In 2013, Alta device, Inc. has successfully demonstrated thin-film GaAs single-junction solar cells with record power conversion efficiency (PCE) of 28.8% by using an epitaxial lift-off (ELO) technique to eliminate the backward spontaneous emission into the substrate[1]. In this work, we aim to further suppressing the spontaneous emission to the front side by adding a selective filter membrane on the thin-film GaAs solar cells. It can effectively reduce the dark current, and thus enhance the open-circuit voltage (Voc) of GaAs thin film solar cells. Regarding the fabrication of thin film GaAs solar cells using the ELO method, the epitaxial layers need to be soaked in the etching solution. Without proper protection, the process likely deteriorates the solar cell performance and lengthens the process time. Therefore, we use a wet chemical etch method to remove the substrate completely, followed by electroplating of Nickle on the back as the carrier. We can successfully manufacture flexible GaAs thin-film solar cells in one quarter of a four-inch wafer. Regarding the fabrication of selective filters, we design and deposit 12 pairs of titanium dioxide (TiO2) and silicon dioxide (SiO2) dielectric stacks, targeting at cutoff wavelengths of 795nm, 858nm, and 915nm. According to the experimental results, the net Voc of the thin-film cells with the 858nm and 915nm cutoffs increased by 0.8 and 3.3mV, respectively, compared to the devices before the deposition of the selective filters. Furthermore, we have successfully developed an optical model that combines a rigorous couple wave analysis (RCWA) and the photon recycling calculation developed by NREL to quantify the Voc enhancement for thin-film GaAs solar cells with different top structures[2]. According to our simulation results, the thin-film device with nearly ideal material quality exhibits a maximal Voc enhancement 42.6mV by introducing a selective filter with the 860nm cutoff. We conclude that light management using spectrally selective optical filter may be vital to pursuit the efficiency limit of high-quality thin-film GaAs solar cells in the near future.
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Shih, Ching yu, and 石謦毓. "Numerical Study of GaAs-Based Dual Junction Quantum Dot Solar Cells." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/79369317880725751388.
Full textAbstract:
碩士國立交通大學
影像與生醫光電研究所
101
A novel combination of quantum dot intermediate band solar cell and dual-junction tandem cell is proposed and studied numerically. We built our device model by using MatlabR coding and commercial software SilvacoR and APSYSR. A proper inclusion of quantum-dot-related carrier absorption is adapted through modified extinction coefficient k, and effective band gap of the device. The final calculation shows the optimal efficiency enhancement is about 1.11 times of the non-quantum-dot embedded device. This design has great potential to realize a triple junction result with a dual-junction photovoltaic device.
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Ho, Kuan-Ying, and 何冠穎. "Optimization of the PEDOT:PSS/SiNW Hybrid Solar Cells and All-Back-Contact GaAs Solar Cells with Two Dimensional Simulation." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/54685960405502594190.
Full textAbstract:
碩士國立臺灣大學
光電工程學研究所
104
The poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)/silicon nanowire (SiNW) hybrid solar cell and the all-back-contact gallium arsenide (GaAs) solar cell are studied in this thesis. We used different simulation methods based on the characteristic of each solar cell to obtain the optical and electrical properties of each solar cell. After analyzing the electrical properties of the PEDOT:PSS/SiNW hybrid solar cell and the all-back-contact GaAs solar cell, further optimization is proposed, respectively. For the PEDOT:PSS/SiNW hybrid solar cell, a numerical model that capable of simulating the organic/inorganic hybrid solar cells was developed. Furthermore, a Gaussian distribution models of tail/interfacial states and trap states are addressed to present this characteristic when simulating the organic/inorganic hybrid solar cells. The 2D-FDTD model was used to model the optical field. After the simulation parameters are verified by fitting the current density-voltage (J-V) curve to the experimental results, the PEDOT:PSS/SiNW hybrid solar cell is optimized. The optimal structure is proposed with a p-type doping Si layer in the SiNW region adjoining to the PEDOT:PSS and an n-type doping Si layer at the rear Si layer near the bottom contact. The highest efficiency of 16.12% could be obtained after the optimization. For the GaAs solar cell, an all-back-contact is employed to the GaAs solar cell. By investigating the electrical properties of the all-back-contact GaAs solar cell, we are able to find the optimum structural design. A thicker base layer can reach a higher generation current, but it can also lead to a higher recombination. Therefore, the base layer thickness is suggested to be 1.5 um. For a wider n-contact width, a higher Jsc can be obtained, but the recombination at the p-n junction region becomes larger, which deteriorates the FF. Consequently, the n-contact width is recommended to be 600 um. The best efficiency up to 25.12% could be achieved with the suggested structure.
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Chang, Kai-Fu, and 張凱富. "Junction Formation and Transport Mechanism in Hybrid n-GaAs/PEDOT:PSS Solar Cells." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/3x5k86.
Full textAbstract:
碩士國立交通大學
應用化學系碩博士班
105
In recent years the combination of inorganic semiconductor and organic polymer materials, usually named hybrid, has attracted a lot of attention due to simple and low temperature fabrication processes with relatively inexpensive cost. In this study, we investigated the interface junction formation properties of n-GaAs/PEDOT:PSS hybrid solar cells on planar substrates by varying the GaAs substrates doping concentrations. The photocurrent, dark saturation current and build-in potential at this hybrid interface are measured by varying n-GaAs doping concentrations. The work function and valence band edge of the polymer are extracted from ultraviolet photoelectron spectroscopy to construct the band diagram of the hybrid n-GaAs/PEDOT:PSS junction. The current-voltage characteristics were analyzed by using pn-junction and Schottky models. The experimental evidences suggested that the interface between n-GaAs and PEDOT:PSS is most likely a Schottky type junction and the current transport is governed by thermionic emission of majority carriers over a barrier.