Rozprawy doktorskie: „Hot carrier solar cell”

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Vezin, Thomas. "Uneven temperatures in hot carrier solar cells : optical characterization and device simulation". Electronic Thesis or Diss., Institut polytechnique de Paris, 2024. http://www.theses.fr/2024IPPAX061.

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Les cellules solaires à porteurs chauds promettent des rendements théoriques supérieurs à 66%. N´néanmoins, les dispositifs réels ont des rendements nettement inférieurs, de l’ordre de 10%. Pour comprendre cette différence, il est nécessaire de complexifier notre compréhension des cellules solaires à porteurs chauds en introduisant des effets non-idéaux. Dans cette thèse, nous étudions deux effets ≪ d’écart de température ≫: (i) l’existence d’un gradient de température dans l’absorbeur (température inhomogène) et (ii) l’existence de deux températures différentes pour les électrons et les trous. Dans le premier cas, nous proposons une description théorique du transport adaptée à cette situation particulière. Nous montrons que le transport est ambipolaire et thermoélectrique, et proposons une expression théorique pour les coefficients de transport. Ensuite, nous proposons une expérience basée sur une mesure hyperspectrale de photoluminescence en régime continu pour caractériser les coefficients de transport. Nous mesurons en particulier le coefficient Seebeck ambipolaire d’un puits quantique de (In,Ga,As)P. Dans le second cas, nous commençons par prouver que la température des électrons et des trous sont toutes deux accessibles par une simple mesure de photoluminescence en régime continu. En effet, l’absorptivité ´e d’un échantillon dépend des distributions des électrons et des trous grâce au terme de ≪ band filling ≫. Cette technique nécessite que l’échantillon soit soumis à une excitation intense, de sorte que les électrons et les trous soient dans un régime dégénère. Enfin, nous avons étudié l’impact de ces deux effets sur l’opération des cellules `a porteurs chauds. Nous avons d’abord calcul ´e le voltage d’une cellule sujette à l’un ou l’autre de ces deux effets d’écart de température, et montré qu’ils sont identiques. Ensuite, nous avons montré que la différence de température entre les électrons et les trous (à température effective fixée) conduit `a une augmentation de l’efficacité de la cellule, de l’ordre de 1 `a 2 points maximum. Cet effet ´ étant limité, il n’est pas nécessaire de caractériser avec précision la température des électrons et des trous, la connaissance de la température effective semble suffisante
Hot-carrier solar cells promise theoretical efficiencies exceeding 66%. However, actual devicesexhibit significantly lower efficiencies, around 10%. To understand this discrepancy, it is necessary to complicate our understanding of hot-carrier solar cells by introducing non-ideal effects. In this thesis, we study two “uneven temperature” effects: (i) the existence of a temperature gradient within the absorber (inhomogeneous temperature) and (ii) the existence of two different temperatures for electrons and holes. In the first case, we propose a theoretical description of transport adapted to this specific situation. We show that the transport is ambipolar and thermoelectric, and we propose a theoretical expression for the transport coefficients. Next, we suggest an experiment based on hyperspectral photoluminescence imaging in steady-state to characterize transport coefficients. In particular, we measure the ambipolar Seebeck coefficient of an (In,Ga,As)P quantum well. In the second case, we begin by proving that electron and hole temperatures s are both accessible through steady-state photoluminescence spectroscopy. Indeed, the absorptivity of a sample depends on the distributions of electrons and holes due to the ”band filling” effect. This technique requires that the sample be subjected to intense excitation, ensuring that the electrons and holes are in a degenerate regime. Finally, we studied the impact of these two uneven temperature effects on the operation of hot-carrier solar cells. We first calculated the voltage of a cell subject to either of these effects and showed that they result in identical cell voltage. We then demonstrated that the temperature difference between electrons and holes (at a fixed effective temperature) leads to an increase in cell efficiency, by about 1 to 2 points maximum. This effect being limited, precise characterization of electron and hole temperatures is unnecessary to design hot-carrier solar cells

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Rodière, Jean. "Optoelectronic characterization of hot carriers solar cells absorbers". Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066703/document.

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La cellule photovoltaïque à porteurs chauds est un dispositif de conversion de l’énergie solaire en énergie électrique dont les rendements théoriques approchent les 86%. Additionnellement à une cellule photovoltaïque standard, ce dispositif permet de convertir l’excédent d’énergie cinétique des porteurs photogénérés, en énergie électrique. Pour cela, le phénomène de thermalisation doit être réduit et des contacts électriques sélectifs en énergie ajoutés. Afin de déterminer les performances potentielles des absorbeurs, tout en surmontant le défi de fabrication des contacts électriques sélectifs, un montage et une méthode de cartographie d’intensité absolue de photoluminescence résolue spectralement ont été utilisés. Ceci a permis d’obtenir la température d’émission et la séparation des quasi-niveaux de Fermi, les deux grandeurs thermodynamiques caractéristiques de la performance des absorbeurs. Dans cette étude, des absorbeurs à base de puits quantiques d’InGaAsP sur substrat d’InP sont utilisés. Les grandeurs thermodynamiques sont estimées et la technique de caractérisation utilisée permet l’accès à des grandeurs tel que le facteur de thermalisation mais aussi un coefficient thermoélectrique, appelé photo-Seebeck. L’analyse quantitative de porteurs chauds dans des conditions pertinentes pour le photovoltaïque est une première ; le dispositif étudié permettrait de dépasser la limite de Schockley-Queisser. Enfin, le dispositif étant muni de contacts des caractérisations électriques sont faites et comparé aux mesures optiques. Afin de mieux comprendre l’évolution des grandeurs thermodynamiques étudiées, une première simulation est proposée
The hot carrier solar cell is an energy conversion device where theoretical conversion efficiencies reach almost 86%. Additionally to a standard photovoltaic cell, the device allows the conversion of kinetic energy excess of photogenerated carriers into electrical energy. To achieve this, the thermalisation process must be limited and electrical energy selective contacts added. In order to determine potential absorber performances and overcome the fabrication challenge of energy selective contacts, a set-up and the related method of mapping absolute photoluminescence spectra were used. This technique allows getting quasi-Fermi levels splitting and temperature of emission, both thermodynamic quantities characteristic of the performance of the absorbers. In this study, absorbers based on InGaAsP multiquantum wells on InP substrate were used. The thermodynamic quantities are determined and allow to access at quantities such as thermalisation rate but also a thermoelectric coefficient, so-called Photo-Seebeck. The quantitative analysis of the hot carriers regime, in relevant conditions for photovoltaic is a first: the analysed device indicates a potential photovoltaic conversion over the Schockley-Queisser limit. At last, as the device is supplied with electrical contacts, electrical characterization are made and compared to optical measurements. A first simulation is proposed to better understand the thermodynamic quantities evolution as a function of the electrical bias

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Rodière, Jean. "Optoelectronic characterization of hot carriers solar cells absorbers". Electronic Thesis or Diss., Paris 6, 2014. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2014PA066703.pdf.

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La cellule photovoltaïque à porteurs chauds est un dispositif de conversion de l’énergie solaire en énergie électrique dont les rendements théoriques approchent les 86%. Additionnellement à une cellule photovoltaïque standard, ce dispositif permet de convertir l’excédent d’énergie cinétique des porteurs photogénérés, en énergie électrique. Pour cela, le phénomène de thermalisation doit être réduit et des contacts électriques sélectifs en énergie ajoutés. Afin de déterminer les performances potentielles des absorbeurs, tout en surmontant le défi de fabrication des contacts électriques sélectifs, un montage et une méthode de cartographie d’intensité absolue de photoluminescence résolue spectralement ont été utilisés. Ceci a permis d’obtenir la température d’émission et la séparation des quasi-niveaux de Fermi, les deux grandeurs thermodynamiques caractéristiques de la performance des absorbeurs. Dans cette étude, des absorbeurs à base de puits quantiques d’InGaAsP sur substrat d’InP sont utilisés. Les grandeurs thermodynamiques sont estimées et la technique de caractérisation utilisée permet l’accès à des grandeurs tel que le facteur de thermalisation mais aussi un coefficient thermoélectrique, appelé photo-Seebeck. L’analyse quantitative de porteurs chauds dans des conditions pertinentes pour le photovoltaïque est une première ; le dispositif étudié permettrait de dépasser la limite de Schockley-Queisser. Enfin, le dispositif étant muni de contacts des caractérisations électriques sont faites et comparé aux mesures optiques. Afin de mieux comprendre l’évolution des grandeurs thermodynamiques étudiées, une première simulation est proposée
The hot carrier solar cell is an energy conversion device where theoretical conversion efficiencies reach almost 86%. Additionally to a standard photovoltaic cell, the device allows the conversion of kinetic energy excess of photogenerated carriers into electrical energy. To achieve this, the thermalisation process must be limited and electrical energy selective contacts added. In order to determine potential absorber performances and overcome the fabrication challenge of energy selective contacts, a set-up and the related method of mapping absolute photoluminescence spectra were used. This technique allows getting quasi-Fermi levels splitting and temperature of emission, both thermodynamic quantities characteristic of the performance of the absorbers. In this study, absorbers based on InGaAsP multiquantum wells on InP substrate were used. The thermodynamic quantities are determined and allow to access at quantities such as thermalisation rate but also a thermoelectric coefficient, so-called Photo-Seebeck. The quantitative analysis of the hot carriers regime, in relevant conditions for photovoltaic is a first: the analysed device indicates a potential photovoltaic conversion over the Schockley-Queisser limit. At last, as the device is supplied with electrical contacts, electrical characterization are made and compared to optical measurements. A first simulation is proposed to better understand the thermodynamic quantities evolution as a function of the electrical bias

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Jiang, Chu-Wei School of Photovoltaic Engineering UNSW. "Theoretical and experimental study of energy selective contacts for hot carrier solar cells and extensions to tandem cells". Awarded by:University of New South Wales. School of Photovoltaic Engineering, 2005. http://handle.unsw.edu.au/1959.4/23065.

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Photovoltaics is currently the fastest growing energy source in the world. Increasing the conversion efficiency towards the thermodynamic limits is the trend in research development. ???Third generation??? photovoltaics involves the investigation of ideas that may achieve this goal. Among the third generation concepts, the tandem cell structure has experimentally proven to have conversion efficiencies higher than a standard p-n junction solar cell. The alternative hot carrier solar cell design is one of the most elegant approaches. Energy selective contacts are crucial elements for the operation of hot carrier solar cells. Besides the carrier cooling problem within the absorber, carrier extraction has to be done through a narrow range of energy to minimise the interaction between the hot carriers in the absorber and the cooler carriers in the contacts. Resonant tunnelling through localised states, such as associated with atomic defects or with quantum dots in a dielectric matrix, may provide the required energy selectivity. A new model in studying the properties of resonant tunnelling through defects in an insulator is proposed and investigated. The resulting calculations are simple and useful in obtaining physical insight into the underlying tunneling processes. It is found that defects having a normal distribution along the tunnelling direction do not reduce the transmission coefficient dramatically, which increases the engineering prospects for fabrication. Silicon quantum dots embedded in an oxide provide the required deep energy confinement for room temperature resonant tunnelling operation. A single layer of silicon quantum dots in the centre of an oxide matrix are prepared by RF magnetron sputtering. The method has the advantage of controlling the dot size and the dot spatial position along the tunnelling direction. The presence of these crystalline silicon dots in the oxide is confirmed by high resolution transmission electron microscopy (HRTEM). A negative-differential resistance characteristic has been measured at room temperature on such structures fabricated on an N-type degenerated silicon wafer, a feature that can be explained by the desired resonant tunnelling process. A silicon quantum dot superlattice can be made by stacking multiple layers of silicon quantum dots. A model is proposed for calculating the band structure of such a silicon quantum dot superlattice, with the anisotropic silicon effective mass being taken into account. It suggests a high density of silicon quantum dots in a carbide matrix may provide the bandgap and required mobility for the top cell in the stacks for the recently proposed all-silicon tandem solar cell. The resonant tunnelling modeling and silicon quantum dot experiments developed have demonstrated new results relevant to energy selective contacts for hot carrier solar cells. Building on this work, the modeling study on silicon quantum dots may provide the theoretical basis for bandgap engineering of all-silicon tandem cells.

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Zhang, Qingrong. "Hot Carriers in Thin-film Absorbers". Thesis, KTH, Skolan för industriell teknik och management (ITM), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-303146.

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Solar energy is one of the most promising sources of confronting the energy crisis. And hot carrier solar cell can be the future to increase the efficiency of solar cells to exceed to the theoretical efficiency limit, Shockley-Queisser limit. After theoretical understanding of some essential aspects of hot carrier solar cell, to better understand the properties of hot carriers and the thermalization mechanisms behind it, analysis is conducted based on the photoluminescence spectra of GaAs thin-film absorber samples with different thicknesses. According to the results of the analysis, information on the properties of hot carriers in thin-film GaAs absorbers will be extracted, as well as a conclusion based on those results.
Solenergi är en av de mest lovande källorna för att konfrontera energikrisen. Och heta bärsolceller kan vara framtiden för att öka solcellernas effektivitet till att överskrida den teoretiska effektivitetsgränsen, Shockley-Queisser-gränsen. Efter teoretisk förståelse av några väsentliga aspekter av varmbärarsolceller, för att bättre förstå egenskaperna hos heta bärare och termismeringsmekanismerna bakom den, utförs analys baserad på fotoluminescensspektra för GaAs tunnfilmsabsorberprover med olika tjocklekar. Enligt resultaten av analysen kommer information om egenskaperna hos heta bärare i tunnfilmiga GaA-absorberare att extraheras, liksom en slutsats baserad på dessa resultat.

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Behaghel, Benoît. "Fabrication and investigation of III-V quantum structured solar cells with Fabry-Pérot cavity and nanophotonics in order to explore high-efficiency photovoltaic concepts : towards an intermediate band assisted hot carrier solar cell". Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066729/document.

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Le photovoltaïque (PV) s’est imposé comme un acteur majeur de l’énergie. L’innovation dans ce domaine passera sans doute par le PV à haut rendement sur des couches minces flexibles et légères permettant son déploiement dans les applications mobiles. Cette thèse étudie le développement de cellules solaires III-V à structures quantiques visant des concepts PV hauts rendements tels les cellules solaires à bande intermédiaire (IBSC). Ces IBSC se sont montrés limités du fait de l’échappement thermique des porteurs à température ambiante ainsi que la faible absorption optique sous le gap. Nous avons évalué la topologie, le mécanisme d’échappement thermique, la structure quantique ainsi que l’absorption de boites quantiques en In(Ga)As dans un matériau hôte en Al0.2GaAs à grand gap. Nous avons aussi caractérisé de manière quantitative comment opère ce système et avons amélioré son design optique. Sous une forte irradiation, nous avons mis en évidence l’apparition d’une population de porteurs chauds dans les boites quantiques. Par ailleurs, l’effet d’absorption sequentielle à deux photons (S-TPA) a été démontré. Nous avons observé une augmentation de ce S-TPA d’un facteur x5-10 grâce à du management de la lumière réalisé notamment avec des cavités de Fabry-Pérot. Des nanostructures périodiques ont aussi été fabriquées dans le cas de cellules solaires à multi-puits quantiques par l’utilisation de lithographie en nanoimpression. Dans l’ensemble cette étude vise à discuter la possibilité de réaliser des cellules solaires à porteurs chauds assistés d’une bande intermédiaire et améliorées par un management optique afin d’ouvrir la voie pour des cellules à hauts rendements
In the past decade, photovoltaics (PV) has become a key player for the future of worldwide energy generation. Innovation in PV is likely to rely on high efficiency PV with flexible and lightweight thin films to enable PV deployement for mobile applications. In the framework of the Japanese-French laboratory “NextPV”, this thesis investigates the development of III-V quantum structured solar cells to explore high-efficiency photovoltaic concepts especially intermediate band solar cells (IBSC). Quantum structured IBSC have proven to be limited by thermal escape at room temperature and by low subbandgap light absorption. Following a consistent approach, we evaluate the topology, thermal escape mechanism, quantum structure and optical absorption of In(Ga)As quantum dots in a wide gap Al0.2GaAs host material. We also characterize quantitatively the device operation and improve the optical design. For a high irradiation, we evidence a hot carrier population in the quantum dots. At the same time, sequential two-photon absorption (S-TPA) is demonstrated both optically and electrically. We also show that S-TPA for both subbandgap transitions can be enhanced by a factor x5-10 with light management techniques, for example by implementation of Fabry-Perot cavities with the different epitaxial transfer methods that we developed. More advanced periodical nanostructures were also fabricated in the case of multi-quantum well solar cells using nanoimprint lithography techniques. Overall we discuss the possibility of realizing intermediate-band-assisted hotcarrier solar cells with light management to open the path for high-efficiency quantum structured IBSC

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Behaghel, Benoît. "Fabrication and investigation of III-V quantum structured solar cells with Fabry-Pérot cavity and nanophotonics in order to explore high-efficiency photovoltaic concepts : towards an intermediate band assisted hot carrier solar cell". Electronic Thesis or Diss., Paris 6, 2017. http://www.theses.fr/2017PA066729.

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Le photovoltaïque (PV) s’est imposé comme un acteur majeur de l’énergie. L’innovation dans ce domaine passera sans doute par le PV à haut rendement sur des couches minces flexibles et légères permettant son déploiement dans les applications mobiles. Cette thèse étudie le développement de cellules solaires III-V à structures quantiques visant des concepts PV hauts rendements tels les cellules solaires à bande intermédiaire (IBSC). Ces IBSC se sont montrés limités du fait de l’échappement thermique des porteurs à température ambiante ainsi que la faible absorption optique sous le gap. Nous avons évalué la topologie, le mécanisme d’échappement thermique, la structure quantique ainsi que l’absorption de boites quantiques en In(Ga)As dans un matériau hôte en Al0.2GaAs à grand gap. Nous avons aussi caractérisé de manière quantitative comment opère ce système et avons amélioré son design optique. Sous une forte irradiation, nous avons mis en évidence l’apparition d’une population de porteurs chauds dans les boites quantiques. Par ailleurs, l’effet d’absorption sequentielle à deux photons (S-TPA) a été démontré. Nous avons observé une augmentation de ce S-TPA d’un facteur x5-10 grâce à du management de la lumière réalisé notamment avec des cavités de Fabry-Pérot. Des nanostructures périodiques ont aussi été fabriquées dans le cas de cellules solaires à multi-puits quantiques par l’utilisation de lithographie en nanoimpression. Dans l’ensemble cette étude vise à discuter la possibilité de réaliser des cellules solaires à porteurs chauds assistés d’une bande intermédiaire et améliorées par un management optique afin d’ouvrir la voie pour des cellules à hauts rendements
In the past decade, photovoltaics (PV) has become a key player for the future of worldwide energy generation. Innovation in PV is likely to rely on high efficiency PV with flexible and lightweight thin films to enable PV deployement for mobile applications. In the framework of the Japanese-French laboratory “NextPV”, this thesis investigates the development of III-V quantum structured solar cells to explore high-efficiency photovoltaic concepts especially intermediate band solar cells (IBSC). Quantum structured IBSC have proven to be limited by thermal escape at room temperature and by low subbandgap light absorption. Following a consistent approach, we evaluate the topology, thermal escape mechanism, quantum structure and optical absorption of In(Ga)As quantum dots in a wide gap Al0.2GaAs host material. We also characterize quantitatively the device operation and improve the optical design. For a high irradiation, we evidence a hot carrier population in the quantum dots. At the same time, sequential two-photon absorption (S-TPA) is demonstrated both optically and electrically. We also show that S-TPA for both subbandgap transitions can be enhanced by a factor x5-10 with light management techniques, for example by implementation of Fabry-Perot cavities with the different epitaxial transfer methods that we developed. More advanced periodical nanostructures were also fabricated in the case of multi-quantum well solar cells using nanoimprint lithography techniques. Overall we discuss the possibility of realizing intermediate-band-assisted hotcarrier solar cells with light management to open the path for high-efficiency quantum structured IBSC

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Hirst, Louise. "A spectroscopic study of strain-balanced InGaAs/GaAsP quantum well structures as absorber materials for hot carrier solar cells". Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/10474.

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In this thesis, five intrinsic loss mechanisms which fundamentally limit solar energy conversion efficiency are identified. The three dominant mechanisms are thermalisation loss, below Eg loss and Boltzmann loss. Targeting these three losses through alternative device design is the only way substantial efficiency enhancement might be achieved. The hot carrier solar cell targets these dominant mechanisms and hence has a theoretical limiting efficiency, under maximum solar concentration, in excess of 80%. Despite clear efficiency advantages, a hot carrier solar cell has never been experimentally demonstrated because two key development challenges remain: energy selective contacts and absorber materials which maintain a hot carrier distribution under realistic levels of incident solar irradiation. In this study, strain-balanced InGaAs/GaAsP QW structures with a range of QW parameters were characterised spectroscopically in order to determine the suitability of this material system as a hot carrier absorber. In a deep, wide well sample, a temperature gradient between the carrier distribution and the surrounding lattice of 150 K was demonstrated using continuous wave photoluminescence spectroscopy. This technique was also used to calculate a thermalisation coefficient for each sample, allowing for comparison with other hot carrier studies. Time resolved photoluminescence measurements were used to identify cooling pathways occurring in this material system. Bi-exponential cooling behaviour was observed, indicating that two different mechanisms with different characteristic cooling lifetimes were dominating carrier cooling. In the deep, wide well sample it was determined that peak LO phonon distribution temperatures of at least 500 K above that of the surrounding lattice would be required to produce the observed carrier cooling.

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Le, bris Arthur. "Etude de faisabilité d'un dispositif photovoltaïque à porteurs chauds". Phd thesis, Ecole Centrale Paris, 2011. http://tel.archives-ouvertes.fr/tel-00646713.

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La cellule photovoltaïque à porteurs chauds se caractérise par une population électronique hors équilibre thermique avec le réseau, ce qui se traduit par une température électronique supérieure à la température du matériau. Il devient alors possible de récupérer non seulement l'énergie potentielle des porteurs, mais également leur énergie cinétique, et donc d'extraire un surcroît de puissance qui n'est pas exploitée dans des cellules conventionnelles. Cela permet d'atteindre des rendements potentiels proches de la limite thermodynamique. L'extraction des porteurs hors équilibre se fait au moyen de membranes sélectives en énergie afin de limiter les pertes thermiques. Dans cette thèse, l'influence de la sélectivité des contacts sur les performances de la cellule est analysée par des simulations de rendement. Il apparaît que ce paramètre est moins critique qu'annoncé dans la littérature, et que des rendements élevés sont possibles avec des contacts semi-sélectifs, permettant l'extraction de porteurs au dessus d'un seuil d'énergie. De tels contacts sont non seulement beaucoup plus facilement réalisables en pratique que des contacts sélectifs, mais sont également plus compatibles avec les densités de courant élevées qui sont attendues dans de tels dispositifs. Une méthodologie expérimentale est également proposée pour analyser la vitesse de thermalisation des porteurs hors équilibre. Des porteurs sont photogénérés par un laser continu et leur température en régime stationnaire est sondée par photoluminescence en fonction de la densité de puissance excitatrice. Un modèle empirique est obtenu reliant la puissance dissipée par thermalisation à la température électronique. Ce modèle est ensuite utilisé pour simuler le rendement de cellules présentant une thermalisation partielle des porteurs. Enfin, un rendement de cellule réaliste présentant une absorption non idéale, une vitesse de thermalisation mesurée sur des matériaux réels et des contacts semi-sélectifs est calculé. Il ressort qu'une augmentation substantielle de rendement est possible en comparaison d'une simple jonction ayant le même seuil d'absorption, mais que la vitesse de thermalisation observée est néanmoins trop élevée pour permettre de dépasser les records de rendement actuels. Des idées sont proposées afin d'améliorer les performances des structures étudiées.

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Ho, Carr Hoi Yi. "Toward better performing organic solar cells: impact of charge carrier transport and electronic interactions in bulk heterojunction blends /Ho Hoi Yi, Carr". HKBU Institutional Repository, 2017. https://repository.hkbu.edu.hk/etd_oa/359.

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Organic photovoltaic (OPV) is an exciting energy harvesting technique. Although its power conversion efficiency (PCE) now exceeds 10% in a research laboratory, the processing window of an OPV cell is still narrow. A fundamental understanding of the OPV materials is desired. This thesis presents the charge carrier transport properties and electronic interactions in the bulk heterojunction (BHJ) active layer of OPV cells. They were found to be well correlated with OPV device performances. Space-charge-limited current (SCLC) measurements and admittance spectroscopy (AS) were employed to study the charge transports, while photothermal deflection spectroscopy (PDS) was used to probe the trap densities inside the materials. Beneficial effects of a common solvent additive, 1,8-diiodooctance (DIO), on PTB7:PC71BM OPV cells have been investigated. With DIO present in the casting solution, the resulting BHJ films have much enhanced electron mobilities, whereas the impact on the hole mobility is negligible. The origin of increased electron mobility is the reduced average electron hopping distance for those films prepared with DIO solvent additive. A balance of hole-electron mobility by tuning the DIO concentration was demonstrated to be the way to optimize the OPV device performance. In light of carrier transport measurement results, a "polymer-rich" strategy with preserved device performance was demonstrated. After understanding the importance of balanced hole-electron mobility, the impact of donor-acceptor weight ratio on the performance of PTB7 : PC71BM based OPV cells was explored. Early stage electronic donor-acceptor interactions were revealed using ultra-low dosages of fullerenes. Before electron transport pathways percolate, the unconnected fullerene domains act as traps and hinder electron transport. From PDS, the trap density observed inside BHJ films was found to be anti-correlated with the fill factor of OPV devices. The origin of low FFs is mainly due to electron traps and localized states from fullerenes. Based on the observations, it is proposed that PC71BM tends to intercalate with PTB7 backbone instead of forming self-aggregates before the electron pathway percolation. Apart from investigating the fundamentals in OPV devices, a solution to improve its processing window was proposed in this thesis. Thermally stable polymer : fullerene OPV cells were fabricated by employing fluorenone-based solid additives. A charge transfer interaction between the additives and donor moiety of polymer formed a locked network which freezes the BHJ morphology under thermal stress. The most promising result retains 90% of the origin efficiency, upon thermal aging at 100 °C for more than 20 hours in PTB7:PC71BM solar cells. Besides fullerene-based OPV, all-polymer photovoltaic solar cells (all-PSCs) were also investigated. Two new difluorobenzene-naphthalene diimide based polymer electron acceptors, one random (P1) and one regioregular (P2) structure, were compared. P2 exhibited a much better molecular packing, a higher electron mobility and more balanced hole-electron mobilities in its composite film with polymer donor, PTB7-Th. An optimized PTB7-Th:P2 device can achieve a respectably high PCE over 5% for all-PSC devices. These all-PSCs should open a new avenue for next generation OPVs.

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Mills, Ted Jonathan. "Direct imaging of minority charge carrier transport in triple junction solar cell layers". Thesis, Monterey, Calif. : Naval Postgraduate School, 2006. http://bosun.nps.edu/uhtbin/hyperion.exe/06Dec%5FMills.pdf.

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Thesis (M.S. in Applied Physics)--Naval Postgraduate School, December 2006.
Thesis Advisor(s): Nancy M. Haegel, Sherif Michael. "December 2006." Includes bibliographical references (p. 63-64). Also available in print.

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Lau, Yin Ping. "Si/CdTe heterojunction fabricated by closed hot wall system". HKBU Institutional Repository, 1995. http://repository.hkbu.edu.hk/etd_ra/44.

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Singh, Surjeet. "Mathematical Modeling of a P-N Junction Solar Cell using the Transport Equations". Wright State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=wright1496054495555896.

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Hsu, Chih-An. "Absorber and Window Study – CdSexTe1-x/CdTe Thin Film Solar Cells". Scholar Commons, 2019. https://scholarcommons.usf.edu/etd/7813.

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CdTe an II-VI semiconductor has been a leading thin film photovoltaic material due to its near ideal bandgap and high absorption coefficient [1]. The typical thin film CdTe solar cells have been of the superstrate configuration with CdS (Eg-2.42eV) as the n-type heterojunction partner. Due to the relatively narrow bandgap of CdS, a wider bandgap n-type window layer has recently emerged as a promising substitute: alloys of MgyZn1-yO have been successfully used as the emitter or window layer. The benefits in the usage of MgyZn1-yO (MZO) are its tunable bandgap and wide optical spectrum on optoelectronic devices. Due to an increasing bandgap of the window layer, the carrier collection can be improved in the short wavelength range (<500 nm). In addition alloys of CdSexTe1-x (CST) have also been used in the absorber layer (i.e., CST/CdTe) for the fabrication of CdTe devices to improve the carrier collection and lifetime [2]. The lower bandgap of the CST alloy can lead to higher short-circuit current (JSC), but it can also result in lower open circuit voltage (VOC). Another critical aspect of the CdTe solar cell is the use of copper as a p-type dopant, which is typically incorporated in the cell during the fabrication of the back contact. The most challenging issue related to further advancing the CdTe solar cell efficiency is the relatively low level of p-type doping, which limits the VOC. Efforts to dope CdTe with group V dopants are yet to produce the desired results. ZnO has been used as an effective high resistivity transparent. When CdTe is deposited directly on sputtered ZnO, VOC of typically 500-600 mV is produced. Band alignment measurements indicate that a negative conduction band offset with CdS exists; alloying with MgO to produce MgyZn1-yO with a composition of y = 0.15 can produce a flat conduction band alignment with CdS. This material has an additional benefit for improving the energy bandgap of the MZO for better UV light transmission in the short wavelengths. By changing the magnesium content from y = 0 to 0.30 allowed researchers to make the tunable conduction band offset from a “cliff” to a “spike,” with both increased open-circuit voltage and fill factor as increasing magnesium compositions [3] — the bandgap gains as expected with increased magnesium composition. The large compositions (y > 0.30) of MgyZn1-yO cause the enormous spike result in S-kink in the IV measurement so that the FF decreases. Besides, due to the instability of MZO material, the fabrication process has to proceed carefully. The properties of CST films and cells were investigated as a function of Se composition (x), substrate temperature (TSUB), and ambient used during the CSS deposition. The higher ratio of Se in CST alloy causes the smaller grain structures and lower bandgap, which profoundly detrimental to the device performance (VOC). However, the CST can be deposited in various substrate temperatures and different inert ambient gas to improve the grain structure by utilizing the especial Close Space Sublimation (CSS) deposition system. Therefore, despite the fact that the CST (25% Se) has the optical bandgap (1.37eV), the improvement of grain structure can slightly increase the doping concentration and decrease the grain boundary (GBs) due to increased alloys grain size 3X larger, which is contributed to improving the VOC [4]. The study of higher ratio Se of CST alloy is significant to achieve the high efficiency polycrystalline CST/CdTe photovoltaic devices. The effect of Cu doping back contact in CdSexTe1-x (CST)/CdTe solar cells with varying amounts of Se (x) has been investigated. The Cu-based back contact was annealed at different thermal temperatures in order to vary the amount of Cu in-diffusion. Net p-type doping was found to increase as the back-contact annealing temperature increased. All cells exhibited a decrease in VOC with increased annealing temperature (i.e., higher Cu concertation), presumably due to a degradation of the lifetime with increased amounts of Cu [5]. However, cells with the highest Se composition appeared to exhibit a higher degree of tolerance to the amount of Cu – i.e., they exhibited a smaller loss in VOC with the increased amount of Cu. Extrinsic p-type doping of CdSeTe can be fabricated using two different experimental processes. Firstly, by using group I elements such as, Cu to substitute Cd, which is promising during the back contact process. Secondly, using group V (P, As, Sb) elements to substitute Te, and this is suitable for Cd-rich of intrinsic CdTe. Intrinsic CST alloy has lower hole density concentration as higher Se composition with limitation of the VOC. Thus, in order to increase the p-type net doping up to 1016 cm-3 the extrinsic P or As doping have been widely investigated recently. The research studies show the CST/CdTe devices lead to improve VOC up to 850 mV with higher hole density in higher Se compositions of As doped CST alloys. Nevertheless, the group V doped CdTe still cause the formation of compensating defects limits the upper boundary of dupability on the CdTe thin film solar cells. Even if a high hole density concentration is achieved for intrinsically-doped p-type CST/CdTe, it is believed the poor carrier lifetime in the CdTe side would still limit the VOC.

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15

Mori, Daisuke. "Development of Polymer Blend Solar Cells Composed of Conjugated Donor and Acceptor Polymers". 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/199331.

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Kotsedi, Lebogang. "Fabrication and characterization of a solar cell using an aluminium p-doped layer in the hot-wire chemical vapour deposition process". Thesis, University of the Western Cape, 2010. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_1349_1363785866.

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When the amorphous silicon (a-Si) dangling bonds are bonded to hydrogen the concentration of the dangling bond is decreased. The resulting film is called hydrogenated amorphous silicon (a-Si:H). The reduction in the dangling bonds concentration improves the optoelectrical properties of the film. The improved properties of a-Si:H makes it possible to manufacture electronic devices including a solar cell. A solar cell device based on the hydrogenated amorphous silicon (a-Si:H) was fabricated using the Hot-Wire Chemical Vapour Deposition (HWCVD). When an n-i-p solar cell configuration is grown, the norm is that the p-doped layer is deposited from a mixture of silane (SiH4) gas with diborane (B2H6). The boron atoms from diborane bonds to the silicon atoms and because of the number of the valance electrons, the grown film becomes a p-type film. Aluminium is a group 3B element and has the same valence electrons as boron, hence it will also produce a p-type film when it bonds with silicon. In this study the p-doped layer is grown from the co-deposition of a-Si:H from SiH4 with aluminium evaporation resulting in a crystallized, p-doped thin film. When this thin film is used in the n-i-p cell configuration, the device shows photo-voltaic activity. The intrinsic layer and the n-type layers for the solar cell were grown from SiH4 gas and Phosphine (PH3) gas diluted in SiH4 respectively. The individual layers of the solar cell device were characterized for both their optical and electrical properties. This was done using a variety of experimental techniques. The analyzed results from the characterization techniques showed the films to be of device quality standard. The analysed results of the ptype layer grown from aluminium showed the film to be successfully crystallized and doped. A fully functional solar cell was fabricated from these layers and the cell showed photovoltaic activity.

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17

Yang, Yiqun. "Integration of photosynthetic pigment-protein complexes in dye sensitized solar cells towards plasmonic-enhanced biophotovoltaics". Diss., Kansas State University, 2016. http://hdl.handle.net/2097/32857.

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Doctor of Philosophy
Department of Chemistry
Jun Li
Solar energy as a sustainable resource is a promising alternative to fossil fuels to solve the tremendous global energy crisis. Development of three generation of solar cells has promoted the best sunlight to electricity conversion efficiency above 40%. However, the most efficient solar cells rely on expensive nonsustainable raw materials in device fabrication. There is a trend to develop cost-effective biophotovoltaics that combines natural photosynthetic systems into artificial energy conversion devices such as dye sensitized solar cells (DSSCs). In this research, a model system employs natural extract light-harvesting complex II (LHCII) as a light-absorbing sensitizer to interface with semiconductive TiO₂ and plasmonic nanoparticles in DSSCs. The goal of this research is to understand the fundamental photon capture, energy transfer and charge separation processes of photosynthetic pigment-protein complexes along with improving biophotovoltaic performance based on this model system through tailoring engineering of TiO₂ nanostructures, attaching of the complexes, and incorporating plasmonic enhancement. The first study reports a novel approach to linking the spectroscopic properties of nanostructured LHCII with the photovoltaic performance of LHCII-sensitized solar cells (LSSCs). The aggregation allowed reorganization between individual trimers which dramatically increased the photocurrent, correlating well with the formation of charge-transfer (CT) states observed by absorption and fluorescence spectroscopy. The assembled solar cells demonstrated remarkable stability in both aqueous buffer and acetonitrile electrolytes over 30 days after LHCII being electrostatically immobilized on amine-functionalized TiO₂ surface. The motivation of the second study is to get insights into the plasmonic effects on the nature of energy/charge transfer processes at the interface of photosynthetic protein complexes and artificial photovoltaic materials. Three types of core-shell (metal@TiO₂) plasmonic nanoparticles (PNPs) were conjugated with LHCII trimers to form hybrid systems and incorporated into a DSSC platform built on a unique open three-dimensional (3D) photoanode consisting of TiO₂ nanotrees. Enhanced photon harvesting capability, more efficient energy transfer and charge separation at the LHCII/TiO₂ interface were confirmed in the LHCII-PNP hybrids, as revealed by spectroscopic and photovoltaic measurements, demonstrating that interfacing photosynthesis systems with specific artificial materials is a promising approach for high-performance biosolar cells. Furthermore, the final study reveals the mechanism of hot electron injection by employing a mesoporous core-shell (Au@TiO₂) network as a bridge material on a micro-gap electrode to conduct electricity under illumination and comparing the photoconductance to the photovolatic properties of the same material as photoanodes in DSSCs. Based on the correlation of the enhancements in photoconductance and photovoltaics, the contribution of hot electrons was deconvoluted from the plasmonic near-field effects.

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森, 大輔. "電子ドナーおよびアクセプター性共役高分子からなる高分子ブレンド薄膜太陽電池の開発". Kyoto University, 2015. http://hdl.handle.net/2433/199528.

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Khan, Imran Suhrid. "In Situ Extrinsic Doping of CdTe Thin Films for Photovoltaic Applications". Scholar Commons, 2018. http://scholarcommons.usf.edu/etd/7177.

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The Cadmium Telluride thin film solar cell is one of the leading photovoltaic technologies. Efficiency improvements in the past decade made it a very attractive and practical source of renewable energy. Considering the theoretical limit, there is still room for improvement, especially the cell’s open circuit voltage (VOC). To improve VOC, the p-type carrier concentration and minority carrier lifetime of the CdTe absorber needs to be improved. Both these parameters are directly related to the point defect distribution of the semiconductor, which is a function of deposition stoichiometry, dopant incorporation and post-deposition treatments. CdTe films were deposited by the Elemental Vapor Transport (EVT) deposition method, which allowed in situ control of the vapor phase stoichiometry (Cd/Te ratio). Extrinsic doping of polycrystalline CdTe by in situ incorporation of antimony (Sb) and phosphorus (P) was investigated. The structural and electrical properties of CdTe thin films and solar cells were studied. Sb and P incorporation were found to increase the net p-doping concentration. Cl and Sb improved the minority carrier lifetime of polycrystalline CdTe, while lower lifetime with Cu and P doped films were indicated. Deep Level Transient Spectroscopy (DLTS) was performed on devices fabricated with different deposition stoichiometry, post-deposition treatments, and phosphorus dopant dose. Several majority and minority carrier traps were identified, and assigned to different point defects based on first principle studies in the literature and experimental conditions used for the deposition and processing of the thin films.

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20

Benner, Frank. "Herstellung, Charakterisierung und Modellierung dünner aluminium(III)-oxidbasierter Passivierungsschichten für Anwendungen in der Photovoltaik". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-205353.

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Hocheffiziente Solarzellen beruhen auf der exzellenten Oberflächenpassivierung, die minimale Rekombinationsverluste gewährleistet. Innerhalb des letzten Jahrzehnts wurde Al2O3 in der Photovoltaikindustrie zum bevorzugten Material für p-leitendes Si. Unterschiedliche Abscheidetechnologien erreichten Passivierungen mit effektiven Minoritätsladungsträgerlebensdauern nahe der AUGER–Grenze. Die ausgezeichnete Passivierungswirkung von Al2O3wird zwei Effekten zugeschrieben: Einerseits werden Si−SiO2-grenzflächennahe Rekombinationszentren passiviert, wenn Wasserstoff, beispielsweise aus der Al2O3-Schicht, offene Bindungen absättigt. Bedingt durch die hohe Konzentration intrinsischer negativer Ladungen an der SiO2-Grenzfläche weist Al2O3 andererseits einen charakteristischen Feldeffekt auf. Das resultierende elektrische Feld hält Elektronen von Oberflächenrekombinationszentren fern. Negative Ladungen im Al2O3 werden generell als fest bezeichnet. Allerdings hat Al2O3 zusätzlich eine hohe Dichte an Haftstellen, die von Elektronen besetzt werden können. Die Dichte negativer Ladungen im Al2O3-Passivierungsschichten hängt vom elektrischen Feld und der Bestrahlungsintensität ab. Ziel dieser Arbeit ist die systematische Untersuchung dielektrischer Passivierungsschichtstapel für die Anwendung auf Si-Solarzellen. Der Qualität und Dicke der SiO2-Grenzschicht kommt in diesem Kontext eine besondere Rolle zu, da sie Ladungsträgertunneln ermöglicht. Der Elektronentransport ist eine Funktion der Oxiddicke und das Optimum zwischen Ladungseinfang und -haltung liegt bei etwa 2 nm SiO2. Vier relevante Al2O3-Abscheidetechnologien werden untersucht: Atomlagenabscheidung, Kathodenzerstäubung, Sprühpyrolyse und Rotationsbeschichtung, wobei die erstgenannte dominiert. Es werden Nanolaminate verglichen, die aus Al2O3 und TiO2, HfO2 oder SiO2 mit subnanometerdicken Zwischenschichten bestehen. Während letztgenannte die Oberflächenrekombination nicht vermindern, beeinflussen TiO2- und HfO2-Nanolaminate die Passivierungswirkung. Ein dynamisches Wachstumsmodell, das initiale und stationäre Wachstumsraten der beteiligten Metalloxide berücksichtigt, beschreibt die physikalischen Parameter. Schichtsysteme mit 0,2 % TiO2 oder 7 % HfO2 sind konventionellen Al2O3-Schichten überlegen. In beiden Fällen überwiegt die veränderte Feldeffekt- der chemischen Passivierung, die mit einer Grenzflächenzustandsdichte von maximal 5·1010 eV−1·cm−2 unverändert auf hohem Niveau verbleibt. Die Ladungsdichte beider Schichtsysteme wird entweder über die Änderung ihrer Polarität der festen Ladungen oder der Fähigkeit zum Ladungseinfang bestimmt. Das Tunneln von Elektronen wird durch ein mathematisches Modell erklärt, dass eine bewegliche Ladungsfront innerhalb der Oxidschicht beschreibt
High-efficiency solar cells rely on excellent passivation of the surface to ensure minimal recombination losses. In the last decade, Al2O3 became the material of choice for p-type Si in the photovoltaic industry. A remarkable surface passivation with effective minority carrier lifetimes close to the AUGER–limit was demonstrated with different deposition techniques. The excellent passivation effect of Al2O3 is attributed to two effects: Firstly, recombination centers at the Si−SiO2 interface get chemically passivated when hydrogen, for instance from the Al2O3 layer, saturates dangling bonds. Secondly, Al2O3 presents an outstanding level of field effect passivation due to its high concentration of intrinsic negative charges close to the SiO2 interface. The generated electrical field effectively repels electrons from surface recombination centers. Negative charges in Al2O3 are generally termed fixed charges. However, Al2O3 incorporates a high density of trap sites, too, that can be occupied by electrons. It was shown that the negative charge density in Al2O3 passivation layers depends on the electrical field and on the illumination intensity. The goal of this work is to systematically investigate dielectric passivation layer stacks for application on Si solar cells. The SiO2 interface quality and thickness plays a major role in this context, enabling or inhibiting carrier tunneling. Since the electron transport is a function of the oxide thickness, the balance between charge trapping and retention is achieved with approximately 2 nm of SiO2. Additionally, four relevant Al2O3 deposition techniques are compared: atomic layer deposition, sputtering, spray pyrolysis and spin–on coating, whereas the former is predominant. Using its flexibility, laminates comprising of Al2O3 and TiO2, HfO2 or SiO2 with subnanometer layers are compared. Although the latter do not show decreased surface recombination, nanolaminates with TiO2 and HfO2 contribute to the passivation. Their physical properties are described with a dynamic growth model that considers initial and steady–state growth rates for the involved metal oxides. Thin films with 0.2 % TiO2 or 7 % HfO2 are superior to conventional Al2O3 layers. In both cases, the modification of the field effect prevails the chemical effect, that is, however, virtually unchanged on a very high level with a density of interface traps of 5·1010 eV−1·cm−2 and below. The density of charges in both systems is changed via modifying either the polarity of intrinsic fixed charges or the ability of trapping charges within the layers. The observations of electron tunneling are explained by means of a mathematical model, describing a charging front, which moves through the dielectric layer

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GOUTSOU, PERRAKI VASSILIKI. "Contribution a l'etude des cellules solaires epitaxiees sur si metallurgique". Paris 7, 1988. http://www.theses.fr/1988PA077138.

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Des photopiles p**(+)pn**(+) ont ete fabriquees par depot epitaxique d'une couche mince de si ultrapur sur un substrat sommairement purifie (umg) p**(+), puis formation de la couche n**(+), des contacts metalliques et de la couche antireflet par serigraphie. Mesures de la longueur de diffusion ln (methode lbic) et de la reponse spectrale des cellules

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22

Huang, Shih-Han, i 黃詩涵. "Carrier Dynamics in Materials for Solar Cell Applications". Thesis, 2012. http://ndltd.ncl.edu.tw/handle/10327427225059706622.

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碩士
國立交通大學
電子物理系所
100
Carrier dynamics in materials for solar cell applications have been investigated by time-resolved photoluminescence. One is InAs self-assembled quantum dots (QDs) covered with a thin AlxGa1-xAs0.8Sb0.2 layer. There is a type I-like transition in type II InAs/GaAsSb QDs due to the recombination of electrons from QDs and holes residing in extended levels composed by the capping layer and the QDs, which is activated by thermal excitation. With the increasing Al content, a blueshift in the QD emission peak and a shortening of the PL decay time are observed, indicating that the band alignment can be controlled by varying the Al content in the AlGaAsSb capping layer. Increasing the valence band offset tend to push the hole wave function into QDs, which in turn improves the overlap between the electron and hole wave functions. According to the experimental results and the theoretical calculations based on eight-band k ⃑∙p ⃑ model, we demonstrate that the AlxGa1-xAs0.8Sb0.2 covered InAs QDs exhibit a type-I band alignment when the Al content exceeds 0.2.Another one is CIGS solar cell. High conversion efficiency in CIGS solar cell is associated with stronger PL intensity and longer carrier lifetime, which is caused by the domination of SRH recombination at room temperature. Besides, radiative recombination in CIGS device is strongly affected by the built-in electric field. Therefore, the intrinsic carrier lifetime can be obtained by injecting higher carrier density.

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23

Chen, Chih-Wei, i 陳致瑋. "Improving carrier collection with graded InGaN based solar cell". Thesis, 2016. http://ndltd.ncl.edu.tw/handle/2876fq.

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碩士
國立中央大學
光電科學與工程學系
105
The tunable band gaps of InGaN, spanning from 3.4eV (GaN) to 0.7eV (InN), make the ternary alloy an attractive material system for photovoltaic devices. Although the absorption of nearly full solar spectrum is theoretically possible with the multi-junction containing properly selected indium compositions, the measured conversion efficiencies of InGaN-based solar cells are typically below 3 %.The unsatisfactory performances can be attributed to many material issues such as the trade-off between long-wavelength absorption and high material qualities, insufficient carrier collection etc. In this work, a single InxGa1-xN layer with graded composition was employed as the active region for nitride-based solar cells. The goal is to increase carrier collection efficiencies and the wavelength range of optical absorption. Three types of solar cells were studied: the graded InxGa1-xN junctions with the lengths of 172 nm and 184 nm, and InxGa1-xN junction with fixed indium composition (x = 0.15). All the devices were grown by metal organic chemical vapor deposition (MOCVD). According to the results of J-V curves under solar illumination and quantum-efficiency spectra, it is found that photovoltaic performances measured with the graded junctions are superior to those obtained with fixed indium content, but lengthening the junction leads to lower efficiencies. The results indicate that carrier collection can be enhanced by the graded conduction and valence band edges. In addition, theoretical analyses based on self-consistent 1D Poisson and Schrödinger equations indicate that polarization effect also plays an important role in photo-current generation.

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24

Shao-JungLu i 呂紹榮. "Influences of the Carrier Transport Layer on the Performances of Perovskite Solar Cell". Thesis, 2017. http://ndltd.ncl.edu.tw/handle/h87f87.

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Hu, Hanlin. "Aggregation of Organic Semiconductors and Its Influence on Carrier Transport and Solar Cell Performance". Diss., 2017. http://hdl.handle.net/10754/625509.

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Photovoltaic technology based on solution-processable organic solar cells (OSCs) provides a promising route towards a low-cost strategy to address the sharply increasing energy demands worldwide. However, up to date, the vast majority of solar cell reports have been based on spin-cast BHJ layers. Spin coating is not compatible with high speed and scalable coating processes, such as blade-coating and slot-die coating, which require the nanoscale morphology to be reproduced in scalable coating methods. And tolerance for thicker BHJ films would also facilitate high speed scalable coating. In the first part of this thesis, we investigate how pre-aggregating the conjugated polymer in solution impacts the charge transport in polymer films. We use P3HT in a wide range of molecular weights in different solvents of common use in organic electronics to investigate how they impact the aggregation behavior in the ink and in the solid state. By deliberately disentangling polymer chains via sonication of the solution in the presence of solvophobic driving forces, we show a remarkable ability to tune aggregation, which directly impacts charge transport, as measured in the context of field effect transistors. The second part of this thesis looks at the impact of the solution-coating method and the photovoltaic performance gap when applying modern BHJ inks developed for spin coating to scalable coating methods, namely blade coating. We ascribe this to significant differences in the drying kinetics between the processes. Emulating the drying kinetics of spin-coating was found to result in performance parity as well as morphological parity across several systems, resulting in demonstration of PTB7:PC71BM solar cells with efficiency of 9% and 6.5% PCEs on glass and flexible PET substrates, respectively. The last part of this thesis looks into going beyond performance parity by leveraging the differences of the scalable coating method to enable highly efficient thick solar cells which surpass the performance of spin-cast devices. High-speed wire-bar coating (up to 0.25 m/s) was used to produce OPV devices with power conversion efficiency (PCE) >10% and significantly outperforming devices prepared by spin-coating the BHJ layer for thicknesses >100 nm by maintaining a higher fill factor.

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Wu, Bing-Rui, i 吳秉叡. "Fabrication of Silicon Thin Films Using Hot-Wire CVD for Solar Cell Applications". Thesis, 2011. http://ndltd.ncl.edu.tw/handle/hq22f9.

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博士
國立中興大學
材料科學與工程學系所
99
Hot-wire chemical vapor deposition (HWCVD) is a promising technique for depositing device-quality thin amorphous, polycrystalline, and epitaxial silicon films at lower temperatures and higher deposition rates. With this technique, deposition species are generated by decomposition reaction of the source gases on the heated filament. Comparing with conventional plasma-enhanced CVD, main advantages of HWCVD are as follows: (1) low deposition temperature, (2) high deposition rate, (3) low equipment cost, (4) large area deposition, (5) high gas utilization, (6) absence of ion bombardment and easy control of the film crystallinity by varying composition of the gas. The primary aim of this dissertation can be divided into two parts: (1) to develop techniques of device-quality silicon films using HWCVD, and (2) to advance applications using silicon films deposited by HWCVD for silicon-base solar cells. A variety of materials, including intrinsic silicon (amorphous, microcrystalline, and polycrystalline), doped silicon (p-type and n-type), and p-type silicon carbide (SiC), was studied to make the films with device-quality. Role of the deposition parameters, mainly including filament temperature, substrate temperature, deposition pressure and gas dilution ratio, were considered to characterize the deposited films. Although the structural, electrical and optical properties can be individually analyzed by means of different characterization techniques, a clear correlation among them was observed. Finally, we produced device-quality intrinsic amorphous silicon films (energy gap (Eg) = 1.6-1.7 eV, dark-conductivity = 2.3×10-11 Ω-1cm-1, and photoconductivity = 6.1×10-4 Ω-1cm-1), poly-Si films (crystalline fraction > 93 %, grain size > 165 nm, Eg = 1.1 eV, dark-conductivity = 8.2×10-8 Ω-1cm-1 and photoconductivity = 1.1×10-5 Ω-1cm-1), n-type microcrystalline silicon (uc-Si) films (dark-conductivity = 0.292 Ω-1cm-1, activation energy (Ea) = 0.036 eV and Eg = 1.95 eV), p-type uc-Si films (dark-conductivity = 0.15 Ω-1cm-1, Ea = 0.05 eV and Eg = 2.18 eV) and p-type SiC films (carrier concentration = 1.03 × 1020 cm-3, Ea = 0.14 eV and dark-conductivity = 3.44 × 10-2 Ω-1cm-1). As the result shown above, those HWCVD deposited silicon films were confirmed to be using for solar cell applications. In this dissertation, a single-sided silicon heterojunction solar cell was fabricated and characterized with the structure of front contact/doped silicon thin emitter/intrinsic silicon thin buffer/mono-crystalline silicon absorber/rear contact. A doped silicon emitter layer is combined with a thin intrinsic amorphous silicon buffer upon a different type mono-crystalline silicon absorber to form the pn-junction cell. Such heterojunction cells had attracted much attention because of their high efficiency and low-cost fabrication process. The cell structure comprises an n-type uc-Si emitter on p-type wafer, laser-annealed n-type poly-Si emitter on p-type wafer, laser-doping patterned n-type uc-Si selective-emitter on p-type wafer, and finally a p-type uc-SiC emitter on n-type wafer. After optimizing the dopant dilution (PH3) for the n-type emitter deposition, a conversion efficiency of 13.35% was achieved for the silicon heterojunction cells with an n-type uc-Si film on the p-type wafer. To improve the n-type emitter properties, a laser crystallization technique is used to reduce the grain boundary defects of HWCVD deposited micro-crystalline n-type films. It was found that the cell performance can be enhanced under an optimum laser power density, where the 14.2% conversion efficiency has been obtained. Furthermore, a laser doping technique was employed to improve the contact resistance between indium-tin oxide and n-type emitter via the formation of the selective emitter structure. By optimizing the laser power density and doping-pattern design, a cell with a selective-emitter structure can achieve an efficiency of 14.31%. For p-type uc-SiC emitter on n-type wafer, a HWCVD deposited p-type uc-SiC film is used as a window layer in n-type crystalline silicon heterojunction solar cells. The effect of hydrogen dilution during p-type silicon carbide deposition on the material properties and cell performance are investigated. The silicon heterojunction cell with an efficiency of 14.5% can be achieved under a hydrogen flow ratio of 75% in the preparation of p-uc-SiC film for. These are very encouraging results for future fabrication of high efficiency heterojunction solar cells by using HWCVD technique.

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Shih-Chen, Wang, i 王世辰. "Investigation on a New Embedded Flash Memory Cell Using a SPICE-compatible Hot Carrier Injection Model". Thesis, 2003. http://ndltd.ncl.edu.tw/handle/71112768521637791024.

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碩士
國立清華大學
電子工程研究所
91
A new embedded-flash-memory cell consisting of two transistors fabricated by a standard CMOS process has been proposed by our lab. The cell is verified with good program and erase characteristics, but further investigation are not completed yet. Owing to the full compatibility with the standard CMOS process, such investigations can be fulfilled by SPICE simulations. Though accurate device characteristics is already obtained by the BSIM device model, but the lack of a sub-circuit model of the gate current injection mechanisms prohibits further studies of the cell behavior. Hence, a simulation tool compatible with SPICE is built up for cell structure optimization. There are two major aims in this study. One is the built-up of the circuit element of hot-carrier injection and a sub-circuit model to simulate the proposed cell. Fairly good agreements between simulation results and the measurement data are obtained with our sub-circuit model. The second aim of this study is to investigate the effect of various cell parameters on the cell behavior. Three kinds of design parameters — cell dimensions, operating voltages, and process variations — are discussed in this work. The influences of design parameters are verified with physical intuitions, hand calculation and simulation results. Through such discussions, the design direction of the novel cell is revealed. Those conclusions therefore can help further improvement of the array structure and new program / erase schemes to obtain better cell performance.

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Hsieh, Pingchen, i 謝秉宸. "Preparation and characterization of silicon-based thin film solar cell by hot-wire CVD". Thesis, 2012. http://ndltd.ncl.edu.tw/handle/65708051191071739257.

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Streszczenie:

碩士
明道大學
材料科學與工程學系碩士班
100
In this study, a self-developed in-line hotwire chemical vapor deposition (HWCVD) system was used for preparing amorphous silicon films for thin-film solar cell applications. The gas flow rate, filament temperature and substrate temperature were varied during the deposition process. The optical, electrical and structural properties of the films were measured using UV-vis spectrometer, scanning electron microscope, Raman spectrometer and surface profiler. The experiment results showed that a film with the best properties of band gap of 1.69 eV, photosensitivity of 3.64×104 and crystallinity of 34% could be deposited with a growth rate of 5.82 Å/s under following conditions: hydrogen gas flow rate of 0 sccm, silane gas flow rate of 20 sccm, filament temperature of 1500°C and substrate temperature of 400°C. Finally, as the film was applied to solar cell fabrication, the solar cell exhibited an open-circuit voltage of 0.65 V, a short-circuit current density of 8.02 mA/cm2, a fill factor of 0.5 and a conversion efficiency of 2.61 %.

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Lin, Hong-Lin, i 林宏霖. "Study of Perovskite Solar Cell Carrier Transporting Layers and Photovoltaics with Lead-free Active Layers". Thesis, 2017. http://ndltd.ncl.edu.tw/handle/srj9et.

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30

Lee, Dong-Lung, i 李東隆. "The Improvement of Hot Carrier Reliability Issues on Embeddable Low Power DINOR Flash Cell With STI Structure". Thesis, 2001. http://ndltd.ncl.edu.tw/handle/81458271778992513299.

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碩士
國立臺北科技大學
機電整合研究所
89
Recently, due to the semiconductor element fabrication technology has developed very rapid in flash memory technology. It has been widely employed in non-volatile semiconductor memories such as: IC card、hand-held Computer、Cameras and so on. The flash memory to act for hard disk drives for data storage must meet the requirement of small size, and low power consumption. For an advanced flash memory, the professor will focus on studying the threshold voltage shift, data retention time, P/E endurance, programming efficiency, erase speed, and so on. The flash memory can obtain higher device reliability, high performance, and integrity. The ULSI application goes on processing faster and voltage supply is trending lower, the more strictly to the technology of flash memory process. Since flash memory technology base on the localized oxidation isolation method (LOCOS) process technology can meet today's high-density requirement. Because of the conventional LOCOS isolation process has a problem known as “bird's beak encroachment”. Therefore, the scalability of the LOCOS is limited to about the um range. To increase the device integration level, different isolation techniques are required. Therefore, when considering the embedded requirement of future SOC (System On Chip) applications a low power flash cell with STI process module become must be. In recent years, it has been expected that STI process will improve both density and integration when compare to LOCOS process; but the local high stress electric field on STI edge will result in SILC (Stress Induced Leakage Current), which degrade the characteristics of data retention. In this thesis, we will investigate flash memory characteristics, which include hot carrier related issues, such as oxide damage, write/erase cycles endurance, read disturbance, data retention and so on in self-aligned flash memory cells and improvement.

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31

Sio, Hang Cheong. "Carrier Recombination in Multicrystalline Silicon: A Study using Photoluminescence Imaging". Phd thesis, 2015. http://hdl.handle.net/1885/101930.

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This thesis applies photoluminescence imaging technique to study various carrier recombination mechanisms in multicrystalline silicon materials. One emphasis of the work has been recombination at grain boundaries, which is one of the limiting factors for the performance of multicrystalline silicon solar cells. An approach for quantifying the recombination activities of a grain boundary in terms of its effective surface recombination velocity, based on the photoluminescence intensity profile across the grain boundary, is developed. The approach is applied to compare the recombination properties of a large number of grain boundaries in wafers from different parts of a p-type boron doped directionally solidified multicrystalline silicon ingot. The results show that varying impurity levels along the ingot significantly impact the electrical properties of as-grown grain boundaries, and also their response to phosphorus gettering and hydrogenation. The work is then extended to various types of multicrystalline silicon materials. The electrical properties of conventionally solidified p-type, n-type and also recently developed high performance p-type multicrystalline silicon wafers were directly compared in terms of their electronic behaviours in the intra-grain regions, the grain boundaries and the dislocation networks. All studied samples reveal reasonably high diffusion lengths among the intra-grain regions after gettering and hydrogenation, suggesting that the main performance limiting factors are likely to be recombination at crystal defects. Overall, grain boundaries in the conventional p-type samples are found to be more recombination active than those in the high performance p-type and conventional n-type samples. As-grown grain boundaries and dislocations in the high performance p-type samples are not recombination active and only become active after thermal processes. In contrast, grain boundaries in the n-type samples are already recombination active in the as-grown state, but show a dramatic reduction in their recombination strength after gettering and hydrogenation. Apart from recombination through crystal defects within the bulk, recombination at surfaces acts as another significant loss mechanism in solar cells. This thesis also demonstrates the use of the photoluminescence imaging technique to study surface recombination in silicon wafers, and provides some examples of such applications.

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32

Lien, Shui-Yang, i 連水養. "Fabrication and Characterization of Silicon Thin Films Using Hot-Wire CVD for Solar Cell Applications". Thesis, 2007. http://ndltd.ncl.edu.tw/handle/71634228508292105093.

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博士
國立中興大學
材料工程學系所
95
Hot-Wire Chemical Vapor Deposition (Hot-Wire CVD) is a promising technique for deposition of amorphous, microcrystalline and polycrystalline silicon thin films for photovoltaic applications. The main advantages of Hot-Wire CVD over PE-CVD, which is currently the most widespread applied technique to deposit thin silicon films in industry, are (1) absence of ion bombardment, (2) high deposition rate, (3) low equipment cost and (4) high gas utilization. Possible issues in Hot-Wire CVD are the control of the substrate temperature and aging of the filaments. This thesis deals with the full spectrum of deposition, characterization and application of amorphous, microcrystalline and polycrystalline silicon thin films. We studied the role of the hydrogen dilution ratio (DH), the substrate temperature (Ts) and the filament temperature (Tf) on the film parameters. Microstructures of the Si films with different deposition parameters have been investigated. It was found that an enhancement of crystallization with the increase of hydrogen dilution ratio, substrate temperature and filament temperature. The hydrogen content (CH) in the film decreases with increase in hydrogen dilution ratio and substrate temperature, but CH increases with increase in filament temperature. A growth mechanism diagnosis for polycrystalline silicon deposition using Hot-Wire CVD is explored in this study. The role of the different parameters involved in the growth mechanism (filament temperature, substrate temperature and hydrogen dilution) was analyzed to optimize the properties of the deposited material. A wide range of microstructure features ranging from purely amorphous to highly crystalline (Xc > 0.93) was achieved after suitably tuning the deposition parameters. High Tf, Ts and/or DH allowed the deposition of highly crystalline material. Furthermore, an abrupt transition from a-Si to poly-Si was observed, especially when the influence of either DH or Ts were analyzed. The ability to deposit both p- and n-type uc-Si doped layers by means of Hot-Wire CVD after the addition of B2H6 and PH3 respectively was evaluated. Both n-type and p-type materials were obtained in a relatively straightforward manner, as similar conditions to those leading to our state-of-the-art intrinsic silicon films could be employed. For n-type uc-Si films, the doping ratio (Sd) of 1 % was used leading to acceptable electrical properties (σd = 0.292 Ω-1cm-1 and EA = 0.036 eV), which allowed the incorporation of this material in photovoltaic devices. In addition, the deposition of p-type uc-Si material proved low σd (~ 0.15 Ω-1cm-1) was obtained when typical doping ratios at 1 % were employed. Finally, we achieved a high efficiency of heterojunction solar cell due to the high optical band gap and low activation energy of n-type and p-type uc-Si prepared by Hot-Wire CVD. The above-mentioned results concerning material properties were applied in the deposition of our first p-type c-Si based heterojunction silicon solar cells grown by Hot-Wire CVD. These preliminary results concerned the analysis of several structures involving different device designs. The proper hydrogen pretreatment and buffer layer used in this work improves of n-layer/c-Si interface. The influences of hydrogen pre-treatment time and n-layer thickness on solar cell performance are studied. We investigated the light trapping effect of a silicon wafer with various pyramidal texture structures by simulation and experimental in this study. Ray-trace simulation in HJ silicon solar cells with various pyramidal texture structures was performed. After optimizing the deposition parameters of n-layer and the H2 pretreatment of solar cell, the single-side HJ solar cell with Jsc = 34.6 mA/cm2, Voc = 0.615 V, FF = 0.71, and efficiency of 15.1 % have been achieved. The double-side HJ solar cell with Jsc = 34.8 mA/cm2, Voc = 0.645 V, FF = 0.73, and efficiency of 16.4 % have been fabricated with optimum textured silicon substrate. The behavior of our HJ solar cells was simulated using a Pc1D simulation program. We present a selection of currently available numerical simulation tools for heterojunction silicon solar cells, and discuss their possibilities and limitations. Afterwards, some results obtained with numerical simulation will be presented. By means of modeling and numerical computer simulation, the influence of series resistance of device, substrate thickness, n-layer emitter thickness, n-layer crystallinity, i-layer thickness and i-layer crystallinity on the solar cell performance (efficiency, open-circuit voltage, short-circuit current, fill factor and internal quantum efficiency) is investigated and compared with experimental results for p-type wafer material. It is the aim of this work to improve the understanding of this device and to derive arguments for design optimization. To evaluate device properties a numerical analysis of the experimental results have been proposed and discussed. After optimizing all the simulated parameters of solar cell, the best results with Jsc = 39.4 mA/cm2, Voc = 0.64 V, FF = 83 % and efficiency = 21 % has been achieved. These are very encouraging results for future fabrication of high efficiency heterojunction solar cells at low temperature by Hot-Wire CVD.

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33

Mao, Hsin-Yuan, i 毛信元. "Hot-Wire Chemical Vapor Deposition of Si-Based Thin Films for Heterojunction Solar Cell Applications". Thesis, 2012. http://ndltd.ncl.edu.tw/handle/48192803861965128807.

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博士
國立中興大學
材料科學與工程學系所
100
Hot-wire chemical vapor deposition (HWCVD) is one of the semiconductor fabrication processes to grow thin film materials. The HWCVD system is composed of vacuum system, gas flow controls, and catalytic wires where Tungsten, Tantalum or Iridium are often used. In a typical HWCVD process, the temperature of wire can increase to 1500~2000 by increasing the DC current. The source gases are entered into the vacuum chamber and decomposed (or catalyzed) by the high temperature wires. The substrate is exposed to one or more volatile precursors which react or decompose on the substrate surface to produce the desired deposit. The dissertation introduces the solar cell research evolution and the lately study of Si film. It also overviews the mechanisms of hot-wire chemical vapor deposition (HWCVD) and plasma enhanced chemical vapor deposition (PECVD). The advantages and the disadvantages of these two CVD are presented and compared. The study in the dissertation is using the HWCVD system and depositing Si based films for photovoltaic applications. The results includes four subjects of “Growth and characterization of intrinsic Si film”, “Deposition and characterization of poly-Si thin films using a two-step growth method”, “Deposition and characterization of p-type nanocrystalline Si (p-nc-Si) films for photovoltaic applications” and “Deposition and characterization of p-type nanocrystalline Si (p-nc-SiC)films for photovoltaic applications”. The intrinsic Si film such as amorphous, microcrystalline and polycrystalline have grown by HWCVD. The influence of deposition parameters such as substrate temperature and hydrogen dilution ratio has been presentation. Based on the identification of hydrogen dilution, a two-step growth method with high/low hydrogen dilution ratios was studied. In the two-step growth process, a thin seed layer was first grown on the glass substrate under high hydrogen dilution ratio and then a thick over layer was subsequently deposited upon the seed layer at a lower hydrogen dilution ratio. The amorphous Si incubation layer could be suppressed greatly in the initial growth of poly-Si film with the two-step growth method. In the subsequent poly-Si film thickening, a lower hydrogen dilution ratio value of the reactant gases can be applied to enhance the deposition rate. The electrical properties were also enhanced. The effects of H2 on the characteristics of p-nc-Si and p-nc-SiC films were analyzed. The optimized parameters of p-nc-Si and p-nc-SiC films were applied as emitter layer in the Si HJ solar cells. The 12.5 % and 14.09 % of photovoltaic conversion efficiencies could be obtained, respectively. These are very encouraging results for the industrial fabrication of high efficiency heterojunction solar cells by using HWCVD technique.

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34

Chiu, Shih-Hsuan, i 邱世璿. "Fabrication of Silicon Carbide Thin Films Using Hot-Wire CVD for Solar-Cell Intrinsic Layer Applications". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/31541904960815976314.

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碩士
國立中興大學
材料科學與工程學系所
98
In this thesis, silicon carbide (SiC) thin films prepared by hot-wire chemical vapor deposition (HWCVD) system was investigated for absorption layer of thin-film solar cells applications. During the deposition, the gas flow rate ratios of SiH4 and CH4 and H2 dilution were varied to study the effects of process conditions on the optoelectronic characteristics and microstructures of SiC thin films. The optimized process conditions of SiC thin film deposition were used to fabricate thin film solar cells. Details of material characteristics of SiC thin films were investigated in terms of x-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectrometer, x-ray diffraction (XRD), Raman spectroscopy, and field-emission scanning electron microscopy (FESEM). Electrical properties of SiC thin films were determined by I-V measurement under AM1.5. The optimum deposition conditions of SiC thin film were SiH4/CH4 ratio of 1 and without H2 dilution. The optical bandgap and ratio of photo- and dark-conductivity of SiC thin film were 1.98 eV and 1000, respectively. In thin film solar cell fabrication, p-type SiC, intrinsic SiC, and n-type microcrystalline Si thin films were prepared on ITO glass substrates by HWCVD system. Al back-electrode was used and prepared by electron-beam evaporation. The efficiency of SiC thin film solar cells was 2.44 %. The further improvement of process conditions on SiC thin film could be performed for tandem solar cells.

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35

Liao, Cheng-Yuan, i 廖正淵. "Numerical Simulation on Carrier Transport in a Thin-Film Amorphous Silicon Solar Cell with a Metal Grating". Thesis, 2012. http://ndltd.ncl.edu.tw/handle/82379087890152825752.

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碩士
國立臺灣大學
光電工程學研究所
100
The carrier transport of a thin-film amorphous silicon (a-Si) solar cell with a metal grating is numerically simulated, for a given generation rate in the solar cell. The solar cell structure consists of three parts: an ITO layer as the top contact, an a-Si layer and a metal Ag grating layer as the back contact. It is a two-dimensional problem to simulate the carrier transport in the a-Si region. Using the Gummel iteration method, we get the self-consistent solutions of the electron and hole continuity equations and the Poisson equation for the entire region of a-Si. At each iteration step, we solve the two-dimensional problem by repeatedly using the related one-dimensional model. In other words, the equations are not solved simultaneously in the two-dimensional region to save the memory and computer time. The simulated results reveal that the maximum efficiency of such a solar cell is enhanced, as compared with the reference flat solar cell of the same volume of a-Si. For the maximum efficiency, it can be increased from 5.93% to 8.24%, with a relative enhancement of about 39%.

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36

Hsieh, Hsin-Yu, i 謝昕佑. "Fabrication and characterization of p-type silicon films using hot-wire chemical vapor deposition for heterojunction solar cell applications". Thesis, 2011. http://ndltd.ncl.edu.tw/handle/qg335a.

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碩士
國立中興大學
材料科學與工程學系所
99
The silicon heterojunction solar cell (SHJPV) has received much attention because of its high conversion efficiency that could be achieved using a simple structure and a low process temperature. In this thesis, the device-quality p-type microcrystalline silicon thin film (p-uc-Si) was fabricated by hot-wire chemical vapor deposition (HWCVD) technique and the effects of wafer specification on the SHJPV cell performance were also investigated. 　　In order to optimize the film quality, the HWCVD p-uc-Si films were fabricated under various hydrogen flow ratios. The film properties were identified by X-ray diffractormeter, field emission scanning electron microscopy, transmission electron microscopy, Raman spectrometer, Fourier-transform infrared spectrometer, Hall measurement and n&k analyzer. The results indicated that the crystallinity of p-uc-Si films was improved with increasing the H2 flow ratio. The optical energy gap, however, decreased as the H2 flow ratio increased. Under an optimum hydrogen flow rate of 50 sccm, a device-quality p-uc-Si film with carrier mobility of 1.38 cm2/V-s and concentration of 1.8x1019 cm-3 was obtained. The SHJPV (Al/ITO/p-uc-Si/intrinsic a-Si/n-wafer/ITO/Ag/Al) with an efficiency of 12.55% can be obtained using the p-uc-Si film as a window layer. 　　For the wafer verification, it was found that the thicker wafer (100 to 675 um) leads to a higher efficiency (11.64 to 12.29 %). The smaller bulk resistivity (140 to 2 ohm-cm) results in a higher efficiency (10.9 to 12.24 %). The longer bulk lifetime (37.5 to 169.5 us) promotes a higher cell efficiency (12.04 to 12.71 %). These indicate that the wafer properties play important roles in determining the cell performance. Finally, the SHJPV with an efficiency of 12.71 % was achieved. This is a very promising result for future high-efficiency and low-cost SHJPVs.

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Chen, Chang-Shian, i 陳昶憲. "The Effects of the Photo-Generation Carrier Distribution on the Properties of Amorphous Si p-i-n thin film Solar Cell". Thesis, 2012. http://ndltd.ncl.edu.tw/handle/52379296585742891173.

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碩士
銘傳大學
電子工程學系碩士班
100
In this paper, theoretical efficiencies for amorphous Si ITO/p/i/n and ITO/p/i/n/Al solar cell are presented by solving the carrier transport equations including optical properties of the cell. Using the optical admittance method including the interference effect, the distribution of the photo-generation carriers in the solar cell under air mass 1.5 global irradiance spectra were obtained numerically. And the carrier distribution in i-layer of solar cell could be treated approximately as a function of exponential decay with a constant bias. First, the surface reflectance and absorption of the solar cell were calculated and the optical limited currents were also estimated according to the absorption in the solar cell. The optimal thickness of the ITO film could be determined to obtain the highest optically limited current. In order to study the effects of the carrier generation distribution, three different kinds of distributions were used in the calculation. For ITO/p/i/n structure, the maximum efficiency under constant carrier generation is 7.07% and the optimum i-layer thickness is 0.4μm. For carrier generation distribution of the G0+Ae^(-αx) and Ae^(-αx), the efficiency and optimum thickness are 7.07%, 0.6 μm and 6.12%, 0.4μm, respectively. Meanwhile, for ITO/p/i/n/Al structure, the maximum efficiency for constant carrier generation is 8.03% and the optimum i-layer thickness is 0.4μm. For carrier generation distribution of the G0+Ae^(-αx) and Ae^(-αx), the efficiency and optimum thickness are 8.23%, 0.5 μm and 7.43%, 0.3μm, respectively. These results show that the distribution of the photo-generation carrier play an important role on the properties of the p-i-n solar cell and is a key factor for designing the optimum performance structure.

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Lebogang, Kotsedi. "Fabrication and characterization of a solar cell using an aluminium p-doped layer in the hot-wire chemical vapour deposition process". Thesis, 2010. http://hdl.handle.net/11394/3441.

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Philosophiae Doctor - PhD
When the amorphous silicon (a-Si) dangling bonds are bonded to hydrogen the concentration of the dangling bond is decreased. The resulting film is called hydrogenated amorphous silicon (a-Si:H). The reduction in the dangling bonds concentration improves the optoelectrical properties of the film. The improved properties of a-Si:H makes it possible to manufacture electronic devices including a solar cell.A solar cell device based on the hydrogenated amorphous silicon (a-Si:H) was fabricated using the Hot-Wire Chemical Vapour Deposition (HWCVD). When an n-i-p solar cell configuration is grown, the norm is that the p-doped layer is deposited from a mixture of silane (SiH4) gas with diborane (B2H6). The boron atoms from diborane bonds to the silicon atoms and because of the number of the valance electrons, the grown film becomes a p-type film. Aluminium is a group 3B element and has the same valence electrons as boron, hence it will also produce a p-type film when it bonds with silicon.In this study the p-doped layer is grown from the co-deposition of a-Si:H from SiH4 with aluminium evaporation resulting in a crystallized, p-doped thin film. When this thin film is used in the n-i-p cell configuration, the device shows photo-voltaic activity.The intrinsic layer and the n-type layers for the solar cell were grown from SiH4 gas and Phosphine (PH3) gas diluted in SiH4 respectively. The individual layers of the solar cell device were characterized for both their optical and electrical properties. This was done using a variety of experimental techniques. The analyzed results from the characterization techniques showed the films to be of device quality standard. The analysed results of the ptype layer grown from aluminium showed the film to be successfully crystallized and doped.A fully functional solar cell was fabricated from these layers and the cell showed photovoltaic activity.

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"A Unified 2D Solver for Modeling Carrier and Defect Dynamics in Electronic and Photovoltaic Devices". Doctoral diss., 2019. http://hdl.handle.net/2286/R.I.55540.

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abstract: Semiconductor devices often face reliability issues due to their operational con- ditions causing performance degradation over time. One of the root causes of such degradation is due to point defect dynamics and time dependent changes in their chemical nature. Previously developed Unified Solver was successful in explaining the copper (Cu) metastability issues in cadmium telluride (CdTe) solar cells. The point defect formalism employed there could not be extended to chlorine or arsenic due to numerical instabilities with the dopant chemical reactions. To overcome these shortcomings, an advanced version of the Unified Solver called PVRD-FASP tool was developed. This dissertation presents details about PVRD-FASP tool, the theoretical framework for point defect chemical formalism, challenges faced with numerical al- gorithms, improvements for the user interface, application and/or validation of the tool with carefully chosen simulations, and open source availability of the tool for the scientific community. Treating point defects and charge carriers on an equal footing in the new formalism allows to incorporate chemical reaction rate term as generation-recombination(G-R) term in continuity equation. Due to the stiff differential equations involved, a reaction solver based on forward Euler method with Newton step is proposed in this work. The Jacobian required for Newton step is analytically calculated in an elegant way improving speed, stability and accuracy of the tool. A novel non-linear correction scheme is proposed and implemented to resolve charge conservation issue. The proposed formalism is validated in 0-D with time evolution of free carriers simulation and with doping limits of Cu in CdTe simulation. Excellent agreement of light JV curves calculated with PVRD-FASP and Silvaco Atlas tool for a 1-D CdTe solar cell validates reaction formalism and tool accuracy. A closer match with the Cu SIMS profiles of Cu activated CdTe samples at four different anneal recipes to the simulation results show practical applicability. A 1D simulation of full stack CdTe device with Cu activation at 350C 3min anneal recipe and light JV curve simulation demonstrates the tool capabilities in performing process and device simulations. CdTe device simulation for understanding differences between traps and recombination centers in grain boundaries demonstrate 2D capabilities.
Dissertation/Thesis
Doctoral Dissertation Electrical Engineering 2019

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40

Williams, Kenrick John. "Electron transfer in sensitized TiO₂ systems studied by time resolved surface second hermonic generation". Thesis, 2012. http://hdl.handle.net/2152/ETD-UT-2012-05-5790.

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Obtaining abundant, clean, sustainable energy has become an increasingly large need globally. To date, solar cells have had a limited impact in meeting energy demands. This is primarily due to their relatively high cost and low power conversion efficiencies. Sensitized solar cells, or Grätzel cells, have the potential for being made with low cost materials, and achieving power conversion efficiency high enough to economically compete with fossil fuels. Understanding the dynamics of charge carriers as they separate at the interface of the light absorbing donor and their semiconducting acceptor becomes an important first step in the realization of an inexpensive and efficient sensitized solar cell. Presented is the theory of treating electrons at donor-acceptor interfaces, and why time-resolved surface second harmonic generation (TR-SHG) is used to probe the dynamics of charge carriers at these interfaces. A series of experiments are described where various preparations of thin films of sensitizers on single crystal titanium dioxide, a common acceptor in Grätzel cells, are prepared and studied. TR-SHG studies of thin films of colloidal PbSe and CdSe QDs showed remarkably different electron cooling and transfer dynamics. The electron cooling in PbSe is thermally activated in PbSe QDs. By cooling samples, electron transfer from higher excited “hot” states was observed. Contrary, for CdSe QDs electron transfer rates were dependent on the energy of the excited state. When higher states were excited, charge transfer rates decreased, indicating that only low energy, electrically “cold”, states participate in charge transfer. When carbon based grapheme QDs are used, the electron dynamics mimic PbSe QDs. In this system, increasing the pump energy leads to slower recombination rates, indicating that electrons have to drift further back to the interface.
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41

Lin, Yang-You, i 林沇佑. "The Impact on Photovoltaic Efficiency with Regards to Defect Densities of Amorphous Silicon Layers and Carrier Recombination Velocity at Interfaces in a Heterojunction Solar Cell Using Silvaco ATLAS". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/15593378593498140236.

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碩士
大葉大學
電機工程學系
98
This study involves the novel heterojunction with intrinsic thin layer (HIT) solar cell structure. Combining the advantages of both crystalline silicon and amorphous silicon, a new structure of silicon-based solar cell was proposed - the heterojunction with an intrinsic thin layer (HIT) solar cell. It has high stability and large light absorption coefficient. It is manufactured under low temperature deposit process, which results in a low cost thin film HIT solar cell with high conversion efficiency. The influence of various layer materials and interfaces on the performance of n-type c-Si based bifacial HIT solar cell has been investigated by using the Silvaco TCAD simulation software. Accordingly, the design optimization of HIT solar cell was proven.

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Benner, Frank. "Herstellung, Charakterisierung und Modellierung dünner aluminium(III)-oxidbasierter Passivierungsschichten für Anwendungen in der Photovoltaik". Doctoral thesis, 2014. https://tud.qucosa.de/id/qucosa%3A29635.

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Hocheffiziente Solarzellen beruhen auf der exzellenten Oberflächenpassivierung, die minimale Rekombinationsverluste gewährleistet. Innerhalb des letzten Jahrzehnts wurde Al2O3 in der Photovoltaikindustrie zum bevorzugten Material für p-leitendes Si. Unterschiedliche Abscheidetechnologien erreichten Passivierungen mit effektiven Minoritätsladungsträgerlebensdauern nahe der AUGER–Grenze. Die ausgezeichnete Passivierungswirkung von Al2O3wird zwei Effekten zugeschrieben: Einerseits werden Si−SiO2-grenzflächennahe Rekombinationszentren passiviert, wenn Wasserstoff, beispielsweise aus der Al2O3-Schicht, offene Bindungen absättigt. Bedingt durch die hohe Konzentration intrinsischer negativer Ladungen an der SiO2-Grenzfläche weist Al2O3 andererseits einen charakteristischen Feldeffekt auf. Das resultierende elektrische Feld hält Elektronen von Oberflächenrekombinationszentren fern. Negative Ladungen im Al2O3 werden generell als fest bezeichnet. Allerdings hat Al2O3 zusätzlich eine hohe Dichte an Haftstellen, die von Elektronen besetzt werden können. Die Dichte negativer Ladungen im Al2O3-Passivierungsschichten hängt vom elektrischen Feld und der Bestrahlungsintensität ab. Ziel dieser Arbeit ist die systematische Untersuchung dielektrischer Passivierungsschichtstapel für die Anwendung auf Si-Solarzellen. Der Qualität und Dicke der SiO2-Grenzschicht kommt in diesem Kontext eine besondere Rolle zu, da sie Ladungsträgertunneln ermöglicht. Der Elektronentransport ist eine Funktion der Oxiddicke und das Optimum zwischen Ladungseinfang und -haltung liegt bei etwa 2 nm SiO2. Vier relevante Al2O3-Abscheidetechnologien werden untersucht: Atomlagenabscheidung, Kathodenzerstäubung, Sprühpyrolyse und Rotationsbeschichtung, wobei die erstgenannte dominiert. Es werden Nanolaminate verglichen, die aus Al2O3 und TiO2, HfO2 oder SiO2 mit subnanometerdicken Zwischenschichten bestehen. Während letztgenannte die Oberflächenrekombination nicht vermindern, beeinflussen TiO2- und HfO2-Nanolaminate die Passivierungswirkung. Ein dynamisches Wachstumsmodell, das initiale und stationäre Wachstumsraten der beteiligten Metalloxide berücksichtigt, beschreibt die physikalischen Parameter. Schichtsysteme mit 0,2 % TiO2 oder 7 % HfO2 sind konventionellen Al2O3-Schichten überlegen. In beiden Fällen überwiegt die veränderte Feldeffekt- der chemischen Passivierung, die mit einer Grenzflächenzustandsdichte von maximal 5·1010 eV−1·cm−2 unverändert auf hohem Niveau verbleibt. Die Ladungsdichte beider Schichtsysteme wird entweder über die Änderung ihrer Polarität der festen Ladungen oder der Fähigkeit zum Ladungseinfang bestimmt. Das Tunneln von Elektronen wird durch ein mathematisches Modell erklärt, dass eine bewegliche Ladungsfront innerhalb der Oxidschicht beschreibt.
High-efficiency solar cells rely on excellent passivation of the surface to ensure minimal recombination losses. In the last decade, Al2O3 became the material of choice for p-type Si in the photovoltaic industry. A remarkable surface passivation with effective minority carrier lifetimes close to the AUGER–limit was demonstrated with different deposition techniques. The excellent passivation effect of Al2O3 is attributed to two effects: Firstly, recombination centers at the Si−SiO2 interface get chemically passivated when hydrogen, for instance from the Al2O3 layer, saturates dangling bonds. Secondly, Al2O3 presents an outstanding level of field effect passivation due to its high concentration of intrinsic negative charges close to the SiO2 interface. The generated electrical field effectively repels electrons from surface recombination centers. Negative charges in Al2O3 are generally termed fixed charges. However, Al2O3 incorporates a high density of trap sites, too, that can be occupied by electrons. It was shown that the negative charge density in Al2O3 passivation layers depends on the electrical field and on the illumination intensity. The goal of this work is to systematically investigate dielectric passivation layer stacks for application on Si solar cells. The SiO2 interface quality and thickness plays a major role in this context, enabling or inhibiting carrier tunneling. Since the electron transport is a function of the oxide thickness, the balance between charge trapping and retention is achieved with approximately 2 nm of SiO2. Additionally, four relevant Al2O3 deposition techniques are compared: atomic layer deposition, sputtering, spray pyrolysis and spin–on coating, whereas the former is predominant. Using its flexibility, laminates comprising of Al2O3 and TiO2, HfO2 or SiO2 with subnanometer layers are compared. Although the latter do not show decreased surface recombination, nanolaminates with TiO2 and HfO2 contribute to the passivation. Their physical properties are described with a dynamic growth model that considers initial and steady–state growth rates for the involved metal oxides. Thin films with 0.2 % TiO2 or 7 % HfO2 are superior to conventional Al2O3 layers. In both cases, the modification of the field effect prevails the chemical effect, that is, however, virtually unchanged on a very high level with a density of interface traps of 5·1010 eV−1·cm−2 and below. The density of charges in both systems is changed via modifying either the polarity of intrinsic fixed charges or the ability of trapping charges within the layers. The observations of electron tunneling are explained by means of a mathematical model, describing a charging front, which moves through the dielectric layer.

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