Dissertationen zum Thema „Passivated contact“

La ricerca nel settore dell’energia fotovoltaica sta portando ad un continuo aumento dell’efficienza delle celle solari. Per raggiungere rendimenti sempre più alti è fondamentale ridurre la perdita di cariche foto-generate, solitamente causata da difetti presenti nel reticolo cristallino o sulle superfici e alle interfacce dei materiali. Tramite la tecnica dei contatti passivanti è possibile rendere inattivi i processi di ricombinazione delle cariche foto-generate. I firing passivated contacts, oggetto di studio in questa tesi, sono un particolare tipo di contatto passivante ottenuto tramite un processo in fase di studio presso il Photovoltaic laboratory (PV-LAB) presso l’Ecole Polytechnique Fédérale de Lausanne (EPFL). Per ottimizzare il processo di fabbricazione, il PV-LAB ha realizzato diversi campioni di materiale semiconduttore con firing passivated contacts. Questi campioni sono stati analizzati in laboratorio tramite la tecnica della surface photovoltage spectroscopy, la quale consiste nella misura della foto-tensione di superficie in uno specifico intervallo di energie. Le misure svolte erano finalizzate a determinare le transizioni elettroniche, indotte dalla luce incidente, che corrispondevano a specifiche caratteristiche del diagramma a bande della struttura, e la struttura del diagramma a bande del campione, non ancora completamente nota. In particolare, si sono analizzate le transizioni energetiche nell’intervallo 0.8-1.1eV. L’attività di laboratorio ha permesso di osservare due diverse transizioni energetiche, comuni a tutti i campioni analizzati. Per mezzo di queste informazioni, e di numerose altre analisi svolte dal PV-LAB, sarà possibile approfondire la conoscenza teorica dei firing passivated contacts, permettendone l’impiego nelle celle solari future ad alta efficienza.

L'industrie PV connaît un fort engouement pour les cellules PERC. Néanmoins leurs performances sont limitées par deux sources de recombinaison des porteurs de charge: au niveau de l'émetteur obtenu par diffusion de P, et en face arrière aux interfaces Al-Si. L'objectif principal de cette thèse vise à limiter ces pertes en intégrant deux nouveaux collecteurs. Le premier est un émetteur sélectif (ES) obtenu par implantation ionique à immersion plasma (PIII) de P. Le second concerne un contact passivé (CP) constitué d'un film de silicium polycristallin (poly-Si) dopé au B sur un oxyde mince. Dans un second temps, les travaux s'intéressent à la compatibilité entre ces collecteurs et les plaquettes de Si issues de lingots fabriqués par solidification dirigée. Un procédé de masquage in situ des implantations PIII a permis d'élaborer des ES avec une bonne maîtrise de la géométrie du motif et des niveaux de dopage. Ensuite, un éventail de techniques pour la métallisation du poly-Si(B) a été étudié. La voie de métallisation par sérigraphie de pâtes traversantes est la plus encourageante à l'heure actuelle. Elle permet l'utilisation de couches hydrogénantes non sacrificielles qui ont mené à l'obtention de précurseurs de cellules avec un excellent niveau de passivation. Néanmoins, la résistance de contact entre le métal et le poly-Si(B) demeure à ce jour trop élevée pour une intégration optimale. Enfin, l'association de Si multicristallin avec différents CP a montré la propension de ces derniers à générer un effet getter externe efficace. Cela laisse envisager une très bonne compatibilité entre l'architecture cellule développée et les Si bas-coût et à faible emprunte carbone
Thanks to a relatively simple fabrication process and high conversion efficiency values the PERC structure is well established at the industrial level. Nevertheless, industrial PERC solar cells performances are mostly limited by two charge carrier recombination sources: P thermally diffused emitter on the front side and the Al-Si interfaces at the rear contacts. The main goal of this work aims at limiting both recombination sources. A selective emitter (SE) obtained by plasma immersion ion implantation (PIII) is developed for an integration on the front side; whereas a B-doped polysilicon (poly-Si) on oxide passivated contact (PC) is integrated on the back side. The second goal of this work consists in evaluating the compatibility between these advanced carrier collectors and directionally solidified Si materials. SE featuring good geometrical properties and a well-controlled doping were fabricated thanks to an in situ localized doping process obtained with a specific mask developed for PIII. Besides, several metal deposition technologies were investigated for the poly-Si(B). Fire-through screen-printing appears as the most promising approach so far. Indeed, the deposition of a non-sacrificial hydrogen-rich layer allowed to reach an excellent surface passivation level for solar cell precursors. However, the specific contact resistivity obtained remains too high for an optimal cell integration. Lastly, the fabrication of poly-Si PC showed excellent external gettering efficiencies for multicrystalline Si. Thus, the potential of the developed cell structure to be integrated with low-cost and low carbon footprint materials is encouraging

Afin de favoriser le déploiement des énergies renouvelables, le développement de cellules solaires moins chères mais aussi plus performantes reste un enjeu pour rendre l’électricité photovoltaïque encore plus attractive. Si les technologies des cellules solaires à base de silicium à homojonction dominent le marché mondial, les performances de ces structures peuvent encore être améliorées. En effet, le contact direct entre la grille métallique et les zones fortement surdopées est source de pertes par recombinaisons des porteurs de charges. L’émergence de de nouvelles structures de cellules émergent à contacts passivés permet des solutions alternatives face à cette limitation. Ces structures visent à délocaliser la prise de contact grâce à l’introduction de couches passivantes entre le substrat de silicium cristallin et la grille de métallisation, diminuant ainsi drastiquement les phénomènes de recombinaisons au sein des dispositifs. La technologie de contacts passivés la plus connue reste celle des cellules à hétérojonction de silicium a-Si:H/c-Si. Cette technologie mature reste pour l’instant limitée car elle représente un nouveau standard industriel mais aussi car elle n’est pas compatible avec les procédés utilisant des températures excédant 250°C. De plus, l’utilisation d’indium, matériau cher et dont la ressource est limitée, dans les couches d’Oxyde Transparent Conducteur (OTC) peut représenter un frein à l’industrialisation de masse du procédé. Il est alors nécessaire de développer de nouvelles technologies de contacts passivés, compatibles avec des procédés à haute température (supérieures à 800°C), et donc intégrables dans une ligne de production existante. Des approches utilisant des OTC en combinaison avec des couches ultraminces d’oxydes, des empilements diélectriques, et des jonctions poly-silicium sur oxyde ont été investiguées afin d’améliorer les performances des cellules à homojonction. Les couches intermédiaires d’OTC développées permettent potentiellement de diminuer les pertes résistives et et celles par recombinaison au niveau des contacts. Ces travaux de thèse se sont ainsi focalisés sur le développement de couches d’oxyde de zinc dopé à l’aluminium (AZO) par pulvérisation cathodique (PC) et Atomic Layer Deposition (ALD) pour les cellules solaires à contact passivés. Ces couches, utilisées seules ou en combinaison avec des matériaux diélectriques, ont été intégrées et testées sur des dispositifs photovoltaïques fonctionnels
For the deployment of renewable energies, the development of cheaper and more efficient solar cells remains an issue to make photovoltaic electricity even more attractive. While homojunction-based silicon solar cell technologies dominate the global market, the performances of these structures can be further improved. Indeed, the direct contact between the metal grid and the highly doped junction is a source of recombination losses. To overcome these limitations, new structures are emerging such as silicon-based passivated contacts solar cells. These structures aim at integrating of passivating layers between the crystalline silicon substrate and the metal grid, thus drastically reducing the recombination phenomena within the devices. Silicon heterojunction (a-Si:H/c-Si) cells remain the most well-known passivated contact technology. Nevertheless, this mature technology is still limited by its fabrication process which is far from the industrial standard, and is hardly compatible with temperatures exceeding 250 ° C. In addition, the use of expensive and potentially toxic indium in the Transparent Conductive Oxide (TCO) layers has restrained up to now the expansion towards mass industrialization of the process. Thus, it is necessary to develop new passivated contacts technologies compatible with high temperature (above 800°C), implementable in a standard production line. This study explores new paths for passivating contact technologies thanks to ultrathin layers of oxides or dielectrics/TCO stacks deposited on silicon homojunctions as well as poly-silicon on thin oxide junctions. In order to limit the resistive losses and potentially limit recombination losses in the contacted areas, intermediate TCO layers have been developed. In this perspective, this works aims at investigating the development of Aluminum Zinc Oxide (AZO) layers by both Magnetron Sputtering (MS) and Atomic Layer Deposition (ALD) for passivated contact solar cells. These layers, also used in combination with dielectric materials have been integrated and then tested in photovoltaic devices

Le marché des modules photovoltaïque est dominé par les technologies basées sur le silicium cristallin (c-Si). L'utilisation de contacts passivés fabriqués à basse température (SHJ) ou haute température (TOPCon) mène à des rendements records (26,8% et 26,2%) proches de la limite théorique de 29,4%. L'option privilégiée par la majorité des acteurs pour dépasser cette limite consiste à associer la technologie c-Si avec un autre matériau semi-conducteur à large bande interdite (EGap) pour permettre une conversion optimale du spectre solaire sur toute la gamme énergétique. L'efficacité maximale théorique de tels dispositifs tandem peut alors atteindre 42%. Il semble avantageux de privilégier une structure à deux terminaux pour simplifier la mise en module et réduire les coûts associés. Cependant, cela implique de fortes contraintes sur les couches d'interface situées entre les deux cellules. En effet, ces dernières doivent alors permettre l'obtention d'excellentes durées de vie des porteurs dans chaque cellule, tout en assurant des propriétés optiques (absorption et réflexion parasites minimales) et électriques (jonction de recombinaison (JR) efficace et peu résistive) optimales.Pour la cellule c-Si, cette thèse se concentre sur la technologie TOPCon qui devrait dominer le marché d'ici 2030. De plus cette approche basée sur des empilements poly-Si/SiOx permet de disposer d'une grande versatilité pour les procédés de fabrication du dispositif tandem (stabilité jusqu'à 800°C), et de bénéficier de couches fortement dopées adaptées à la formation de JR. Le choix de l'absorbeur à large EGap s'est porté sur la technologie pérovskite (Pk) qui semble faire l'unanimité car elle combine potentiellement de faibles coûts de production et de hauts rendements. L'interface entre les deux cellules (TOPCon et Pk) du dispositif tandem est habituellement réalisée avec des couches d'oxydes transparents conducteurs comme l'ITO (Oxyde d'Indium Etain), permettant l'obtention d'excellentes propriétés électriques et optiques. L'indium est cependant un matériau critique qui pourrait limiter le développement de cette technologie à long terme. L'objectif de cette thèse consiste ainsi à explorer des approches sans indium pour l'interface des cellules tandem Pk/c-Si.Les études réalisées dans ces travaux concernent des cellules tandem Pk/c-Si en configuration nip, pour lesquelles deux approches alternatives sont étudiées pour l'ingénierie d'interface. La première n'utilise aucune couche d'interface additionnelle, et la seconde intègre une couche nc-Si (n+) pour former une diode tunnel en silicium afin d'obtenir un courant de recombinaison optimal. Ces deux approches alternatives ont mené à l'obtention de meilleures performances initiales que le procédé de référence, principalement en s'affranchissant de la problématique de court-circuits dans la cellule Pk. Les dispositifs tandem fabriqués sans couche d'interface permettent d'obtenir des facteurs de forme comparables à ceux des meilleurs dispositifs mondiaux (> 81%) ainsi que des rendements proches de 25%, démontrant le potentiel des contacts passivés TOPCon pour la formation de JR sans ITO. Ces deux technologies d'interface sans indium se sont cependant révélées limitées par l'apparition au cours du temps de résistances séries internes. Des caractérisations avancées expliquent ces dégradations par l'apparition d'une couche de SiOx entre le silicium et le SnO2 (la couche sélective d'électron - ESL- de la cellule Pk).En conclusion, les contacts passivés TOPCon sont particulièrement adaptés à la formation de jonctions de recombinaison (directes ou par le biais de diode tunnel en silicium) permettant de s'affranchir d'indium dans les couches d'interconnexion. Le silicium étant particulièrement sensible à l'oxydation, le choix de la couche de contact (ESL en configuration nip) devrait se porter sur un matériau ne comportant pas d'oxygène ou présentant une affinité pour l'oxygène plus forte que le silicium
The photovoltaic module market is dominated by technologies based on crystalline silicon (c-Si). The use of low temperature (SHJ) or high temperature (TOPCon) passivated contacts leads to record efficiencies (26.8% and 26.2%) close to the theoretical limit of 29.4%. The option explored by the majority of institutes to overcome this limit is to combine c-Si technology with another wide bandgap (EGap) semiconductor material to enable optimum conversion of the solar spectrum over the entire energy range. The theoretical maximum efficiency of such tandem devices can then reach 42%. A two-terminal structure enables easiest module processing leading to reduced production costs. However, this places severe constraints on the interface layers between the two cells. These must provide excellent carrier lifetime in each cell, while ensuring optimal optical (minimal parasitic absorption and reflection) and electrical (efficient and highly conductive recombination junction RJ) properties.For the c-Si cell, this thesis focuses on TOPCon technology, which is expected to become market mainstream by 2030. This approach, based on poly-Si/SiOx stacks, offers great versatility for the tandem device fabrication processes (stability up to 800°C), and benefits from highly doped layers that are well suited for the formation of RJ. Among the variety of large EGap materials, perovskite (Pk) technology is the most popular solution as it benefits from both high efficiency potential and low production costs. The interface between the two cells (TOPCon and Pk) of the tandem device is usually formed by transparent conductive oxides layers such as ITO (Indium Tin Oxide), which shows excellent electrical and optical properties. However, indium is a critical material that could limit the long-term development of this technology. Therefore, the aim of this thesis is to explore indium-free approaches for the interface of Pk/c-Si tandem cells.The studies carried out in this work concern Pk/c-Si tandem cells in nip configuration, for which two alternative approaches for interface engineering are investigated. The first one uses no additional interface layer, while the second one integrates an nc-Si (n+) layer to form a silicon tunnel diode, which should provide an optimal recombination current. These two alternative approaches allowed better initial performances than the reference process, mainly by overcoming short-circuit issues in the Pk cell. Tandem devices featuring no additional interface layer show fill factors comparable to those of the world's best devices (>81%) and efficiencies close to 25%, confirming the potential of TOPCon passivated contacts to form indium-free RJ. However, these two indium-free approaches were limited by the appearance of internal series resistance over time. Advanced characterisations explain these degradations by the formation of a SiOx layer between silicon and SnO2 (the electron-selective layer - ESL- of the Pk cell).In conclusion, TOPCon passivated contacts are particularly well suited to obtain efficient recombination junctions (direct or via silicon tunnel diodes), thus eliminating the need to use indium in the interface layers. As silicon is particularly sensitive to oxidation, the choice of contacting layers (ESL in nip configuration) should be focused on a material that contains no oxygen or has a stronger affinity for oxygen than silicon

Dans le contexte des cellules photovoltaïques (PV) à base de silicium cristallin (c-Si), le développement de structures de contacts dits « passivants », qui permettent de limiter les pertes par recombinaisons des porteurs de charge à l’interface entre le métal et le c-Si, est un des principaux leviers vers l’obtention de plus hauts rendements. Une approche de contacts passivés consiste à intégrer entre le métal et le c-Si une jonction composée d’une couche de silicium poly-cristallin (poly-Si) fortement dopée sur une mince couche d’oxyde de silicium (SiOx < 2 nm).Les objectifs de ce travail sont d’une part de développer une jonction poly-Si/SiOx compatible avec la fabrication industrielle des cellules PV, et d’autre part d’améliorer la compréhension des mécanismes de passivation et de transport des charges au niveau de la fine couche de SiOx située à l’interface entre le poly-Si et le c-Si.Dans ce travail, une jonction de poly-Si/SiOx dopée au bore a été développée, le dopage de la couche étant dans un premier temps réalisé in-situ pendant l’étape de dépôt chimique en phase vapeur assisté par plasma (PECVD) de la couche poly-Si. La méthode de dépôt PECVD est répandue dans l’industrie PV et permet la fabrication de la couche poly-Si d’un seul côté du substrat c-Si. Cependant, elle induit une forte concentration d’hydrogène dans la couche déposée, ce qui entraine la formation de cloques à l’interface avec le c-Si et tend à dégrader les propriétés de passivation de surface de la jonction après recuit de cristallisation. L’optimisation des conditions de dépôt (température de dépôt et ratio de gaz H2/SiH4) a permis d’obtenir des couches de poly-Si dopées in-situ intègres. Par la suite, une méthode de dopage alternative, par le biais du dépôt d’une couche diélectrique riche en bore sur le poly-Si, a été appliquée afin de réduire l’apport en hydrogène pendant le dépôt et d’obtenir des couches de poly-Si intègres plus épaisses. L’ajout d’une étape d’hydrogénation a permis d’obtenir des propriétés de passivation de surface au niveau de l’état de l’art pour les deux types de jonctions poly-Si/SiOx développées.A la suite du développement de la jonction poly-Si/SiOx, la caractérisation physico-chimique de la couche SiOx a été réalisée et a démontré une possible amélioration de la stœchiométrie de la couche vers SiO2 ainsi qu’une dégradation de son homogénéité en épaisseur sous l’effet du recuit de cristallisation à haute température. Ces phénomènes pourraient s’expliquer par une diffusion des atomes d’oxygène à l’interface. D’autre part, l’étude du transport des charges à travers le SiOx par C-AFM a mis en évidence les limites de cette technique quant à la détermination de nano-ouvertures au sein de la couche SiOx (qui favoriseraient le transport des charges). Enfin, une méthode de caractérisation des défauts recombinants à l’interface entre une jonction de poly-Si intrinsèque et le c-Si a été mise en œuvre. Cette méthode a permis de modéliser les recombinaisons à l’interface poly-Si/c-Si via deux défauts discrets apparents dont les niveaux d’énergie dans la bande interdite et les ratios de sections efficaces de capture des électrons et des trous ont été déterminés
In the context of high efficiency solar cells (SCs) based on crystalline silicon (c-Si), the development of "passivating" contact structures to limit the recombination of charge carriers at the interface between the metal electrode and the c-Si has been identified as the next step to further improve the photovoltaic (PV) conversion efficiency. Passivating contacts consisting of a highly doped poly-crystalline silicon layer (poly-Si) on top of a thin layer of silicon oxide (SiOx ≤ 2 nm) are particularly sparking interest as they already demonstrated promising conversion efficiency when integrated in SCs.The objectives of this work are to develop a poly-Si/SiOx passivating contact compatible with the industrial production of c-Si SCs, and to investigate the passivation and charge transport mechanisms in the region of the thin SiOx layer located at the interface between the poly-Si and the c-Si.In this work, a boron-doped poly-Si/SiOx contact was fabricated. The doping of the layer was first performed in-situ during the deposition of a hydrogen-rich amorphous silicon (a-Si:H) layer by plasma-enhanced chemical vapor deposition (PECVD). The PECVD step was followed by an annealing step for crystallization of the poly-Si layer. The PECVD presents the advantages of being widespread in the PV industry and enabling the fabrication of the poly-Si contact on a single side of the c-Si substrate. However, it induces a high concentration of hydrogen in the deposited layer, which causes the formation of blisters at the interface with the c-Si and tends to degrade the surface passivation properties of the contact after annealing for crystallization. The optimization of the deposition conditions (temperature and H2/SiH4 gas ratio) enabled to obtain blister-free in-situ doped poly Si layers. An alternative doping method consisting of the deposition of a boron-rich dielectric layer on top of the poly-Si layer was applied to reduce the hydrogen content of the deposited layer. This approach enabled to obtain thicker blister-free poly-Si layers. The diffusion of hydrogen in the contact after annealing is known to provide a further chemical passivation of the poly-Si/c-Si interface. In this work, the addition of a hydrogenation step enabled to obtain state-of-the-art surface passivation properties for the two types of poly Si/SiOx contact fabricated.After developing the poly-Si/SiOx contact, a study of the effect of the annealing step on the chemical and structural properties of the SiOx layer was performed. Results indicated a possible improvement of the stoichiometry of the layer towards SiO2 as well as a degradation of its homogeneity at the poly-Si/c-Si interface after annealing at high temperature. These phenomena could be explained by a diffusion of the oxygen atoms content in the interfacial SiOx layer. The transport mechanism of charge carriers through the SiOx layer was conducted by C-AFM. This study revealed the limits of this technique to determine the presence of pinholes within the SiOx layer (that would help the transport of charge carriers). Finally, a method for characterizing recombinant defects at the interface between an intrinsic poly-Si junction and the c-Si has been developed. This method enabled to model the recombination phenomena at the poly-Si/c-Si interface via two apparent discrete defects. Their associated energy levels in the bandgap and ratios of electron and hole capture cross sections were estimated

The objective of the research in this thesis is to develop manufacturable high-efficiency silicon solar cells at low-cost through advanced cell design and technological innovations using industrially feasible processes and equipment on commercial grade Czochralski (Cz) large-area (239 cm2) silicon wafers. This is accomplished by reducing both the electrical and optical losses in solar cells through fundamental understanding, applied research and demonstrating the success by fabricating large-area commercial ready cells with much higher efficiency than the traditional Si cells. By developing and integrating multiple efficiency enhancement features, namely low-cost high sheet resistance homogeneous emitter, optimized surface passivation, optimized rear reflector, back line contacts, and improved screen-printing with narrow grid lines, 20.8% efficient screen-printed PERC (passivated emitter and rear cell) solar cells were achieved on commercial grade 239 cm2 p-type Cz silicon wafers.

碩士
國立中央大學
材料科學與工程研究所
105
Compared with III-V photodetector, Silicon based photodetector has 10 to 100 times higher dark current, so decreasing dark current is an important topic. In the past, Silicon based component reduces the surface recombination rate through the passivation layer to achieve the purpose of reducing the dark current of the component. However, there is no passivation layer between the metal and semiconductor. In order to solve the above problems, A technology call ‘‘passivated contact’’ is proposed to reduce the carrier recombination between the metal and the semiconductor. This structure is inserted the ultra-thin passivation film between the metal and semiconductor, it can achieve a good passivation effect and the carrier can tunnel the passivation. Rencently, this structure is mostly used in solar cells, but the solar cell structure is similar to photodetector, so this propasal of this research is to investigate the passivated contact, and apply it to the silicon based photodetector to lower the dark current density. The ultra-thin oxide layer is the key to passivated contact, so this study first grows the oxide layer in different methods and discusses its properties, and then stacks the silicon nitride on the oxide layer to enhance the overall passivation effect. The experimental results show that Through RTA annealing interval of 200 degrees to 800 degrees to enhance the passivation properties, the passivated contact can measure the maximum lifetime is 1515us, iVoc is 650mV at 400 degrees. In order to enhance the carrier transport capacity of this structure, we use dry etching to reduce the thickness of silicon nitride from 80nm to 15nm. Finally, passivated contact is applied to the silicon-based photodetector. The experimental results show that the passivated contact of the silicon nitride and the oxide layer can reduce the dark current of the photodetector from 1.44x10-7 to 5.42x10-9 A, dark Current density of up to 1.93x10-5 mA/cm2. In addition, it was also investigated that indium tin oxide covered with this passivated contact structure and found that the component dark current was reduced to 5.36x10-9A, and the responsibility of 0.658 A / W at an operating bias of -5 V.

碩士
中原大學
電子工程研究所
89
GaAs related compound material system dominates the applications of modern high frequency communication devices because of its low noise, high electron mobility and nature of semi-insulating substrate. Recently SiGe technologies developed by IBM, which can be integrated with low cost Si process tremendously progress and affect the mainstream position in GaAs of high frequency ICs. The most important mission for GaAs systems is to promote the high frequency performance and maintain lowers production cost at the mean time. To lower the production cost of GaAs processes new methods need to adopt the process of Si integrated circuits. The first problem often found in the processing of Si integrated circuits is to avoid using gold-alloyed contact meal. When using Al for contact metal in the GaAs material system the problem of “purple plague” will arise. In this study, we develop methods of non-gold alloyed contact metal for GaAs material system and surface treatment of GaAs to reduce the surface density of states. During the processing of S passivation it is found that the higher temperature(-30~80℃) GaAs been passivated the less surface density of states GaAs shows. For example, from 0.559eV increases to 0.836eV. By increased the passivation time (15~60 second) of SF6 , the best result was found about 0.68ev for . By increasing the pressure (10~60mTorr) of SF6 plasma process, the best result was found about 0.607eV for . After the passivation experiment, Co is used to replace Ni that is the common part for Ni/AuGe ohmic contact metal of n-GaAs. Finally non-gold alloyed ohmic contact metal Co/Ge/Al was formed as well as S passivation. The contact resistance ρc as low as 4.1×10-6(Ω-cm2) is found in Co/Ge/Al which is not lower than tradition ohmic contact Ni/AuGe for GaAs. However, superior performance of thermal stability and surface flatness for Co/Ge/Al is found compared to those of Ni/AuGe as well as the consideration of processing cost.

碩士
國立中央大學
光電科學與工程學系
107
With the development of the optoelectronic industry, when the performance reaches a certain bottleneck, the appearance of the passivation layer greatly improves the performance of the optoelectronic components. However, there is no passivation layer between the metal and the semiconductor, some research teams have studied to complete the passivation by means of local opening. However, the opening of the hole will cause serious carrier recombination, therefore the technique of passivating contact will come into being. The thin film is the key to passivation contact. When the single-layer passivated contact film is developed to a certain level, the structure of the single layer cannot meet the requirements of the component, so the passivation contact film of the compound film is proposed. The composite passivation contact film has better passivation effect than the single-layer passivation contact, so this study applied it to the photodetector and studied its component characteristics. In this study, we use wet chemical oxidation method to grow silicon oxide film, and we try the different parameters of wet chemical oxidation method to find the best silicon oxide film with the highest density and low leakage current. Then silicon nitride film is deposited on the silicon oxide film to achieve the effect of compound film of passivation contact. After rapid thermal annealing treatment, it is found that the compound film has the best passivation effect at 500 °C, with the highest lifetime of 1021.25μs and iVoc of 652.4mV. Then we will fabricate the devices of different silicon nitride thickness and measure their electrical properties. Finally, the compound film of passivation contact is applied to the silicon-based photodetector. Indium tin oxide was deposited on compound films for improving the responsibility. The results show that when the compound film of passivation contact is made by using silicon oxide 1.5nm of thickness and silicon nitride 1.7nm, it has the best passivation effect, and the dark current of the photodetector can be reduced from 4.36x10-7A to 8.25x10-9A, photon responsibility of 0.582 A/W at a laser light source of 850 nm.

碩士
國立中央大學
光電科學與工程學系
105
In the silicon solar cell surface passivation has always been an important goal of design and optimization. In the early, the back electric field passivation has been stuided, and later researchers began to study the positive silicon nitride passivation, when the front passivation has been studied, the researchers also began to move the target to another serious compound area - the back surface of the cell. In the 1990s, the University of New South Wales (UNSW) began to introduce passivated PECR / PERL design of the dielectric layer to solve the problem of passivation on the back, but the serious recombination rate at the opening can not be resolved, so began to study hope to be able to solve the opening problem, passivated contact technology began to be raised. In this study, silicon nitride film was deposited on silicon oxide films by wet chemical oxidation, photo-oxidation oxidation and plasma enhance chemical vapor deposition. The lifetime of silicon wafer was measured. FTIR can be seen from the figure that the position of the Si-O-Si bonding at the position of 1080 cm-1 by the wet chemical oxidation method. In this study, the silicon oxide film was grown by wet chemical oxidation method, and the change of different parameters. With the heat treatment, the lifetime can be increased to 1108 us, and the characteristics of film passivation were discussed. To find a structure of high density and low leakage current density of silicon oxide film. Finally, the silicon oxide film was applied to the silicon solar cell, and the silicon solar cell with no silicon oxide film is compared with the photoelectric conversion efficiency. The open-circuit voltage of the silicon solar cell with the passivation layer was increased from the original 551 mV to 625 mV (up 13%), short circuit current 29.8 mA, fill factor 0.59, efficiency from 10.8% to 11.5%.

碩士
國立虎尾科技大學
光電工程系光電與材料科技碩士班
104
In this study, improved photovoltaic characteristics of passivated emitter and rear contact monocrystalline silicon solar cells (PERC) were demonstrated by electroplated copper technology. In general, high recombination velocity of screen-printed monocrystalline silicon solar cells (SPMSSCs) with aluminum paste as the back electrode was presented. Moreover, the series resistance of the SPMSSCs with aluminum paste was still high due to glass powder in aluminum paste. To improve these disadvantages, combined aluminum oxide (Al2O3) formed by metal-organic chemical-vapour-deposition (MOCVD) and silicon nitride (Si3N4) formed by plasma-enhanced chemical-vapour-deposition (PECVD) as passivation layer of PERC were investigated. Varoius laser grooves with various contact areas were formed by the Nd : YAG laser with a wavelength of 1064 nm. The laser parameters include various powers, the focus, the width, the laser dope, and the patterns. The laser damage and residue were removed by potassium hydroxide (KOH) solution. Simultaneously, the series resistance of the PERC was reduced by the nickel silicide/electroplating copper stacked films. Various parameters, including the thickness of the nickel seed layer, the electroplated time, the back passivation layer effects, were used to enhance the photovoltaic characteristics of the PERC. The results suggest that the conversion efficiencies of the PERC was demonstrated by the laser power of 7 %, the laser focus of 0 degree, the laser width of 5. The laser damage was removed by the potassium hydroxide solution with 1.1% for 1 min. The excellent nickel silicide was demonstrated by the nickel seed layer of thermal evaporated 500 nm and annealed at 400 ℃ for 7 min. A conversion efficiency of 15.8% with a open voltage (Voc) of 627 mV, a short current density (Jsc) of 31.4 mA/cm2, and a fill factor (F.F) of 0.745 were demonstrated by electroplated copper current density of 30 mA/cm2 for 40 minutes.

碩士
國立虎尾科技大學
光電工程系光電與材料科技碩士班
105
In this study, the effects of aluminum oxide and silicon nitride stacked films on photovoltaic characteristics of passivated emitter and rear contact silicon solar cells were investigated. In general, the backside electrode of the screen-printed moncrystalline silicon solar cells was formed by screen-printed aluminum paste. However, the recombination rate of aluminum paste/p-type silicon interface is not good. Thus, the aluminum oxide (Al2O3) formed by atomic layer deposition (ALD) and metal organic chemical-vapor-deposition (MOCVD) as well as silicon nitride (SiNx) passivation layer formed by plasma enhanced chemical-vapor-deposition (PECVD) were investigated. By tuning the thickness and the composition of both Al2O3 and SiNx, the high quality stacked passivation layers were addressed. Moreover, the contact process of the Al2O3/SiNx stacked passivation layer were achieved by laser and wet chemical etching technique. The Nd:YAG laser with the wavelength of 1064 nm and the KOH solution for laser damage removal were presented for contact process. Regarding to the wet chemical etching technique, screen-printed polymer paste and the BOE etching solution were used for contact process. The results indicate that the Al2O3 thin film with interface trap charge of 2.061010 cm-2ev-1 deposited by ALD was better than that of MOCVD with interface trap charge of 1.741011 cm-2ev-1. The various thicknesses of silicon nitride ranged from 140 to 300 nm and aluminum oxide ranged from 10 to 30 nm were investigated. The results show that the better conversion efficiency (CE) was presented by combined the SiNx thickness of 180 nm with the Al2O3 thickness of 20 nm. Moreover, the composition effects of the SiNx were investigated by tuning SiH4/(SiH4+NH3) ratio. The results indicate that a good CE was achieved by the SiH4/(SiH4+NH3) at 0.45. Furthermore, the composition effects of the Al2O3 were investigated by tuning exposure time of trimethyl aluminum (TMA) and H2O. The results show that a good CE was demonstrated by the TMA with 0.04 s and H2O with 0.5 s exposure time. Finally, a good contact process was demonstrated by the laser with 1 W. According to the best parameters, a CE of 17.4 % with an open-circuit voltage (Voc) of 627 mV, and a short-circuit current density (Jsc) of 34.2 mA/cm2 were demonstrated in this work.

碩士
國立虎尾科技大學
光電工程系光電與材料科技碩士班
106
In this study, the effects of screen-printed and atomic-layer-deposition (ALD) aluminum oxide (Al2O3) stacked films on photovoltaic characteristics of passivated emitter and rear contact (PERC) silicon solar cells were investigated. In general, the backside electrode of the screen-printed monocrystalline silicon solar cells was formed by aluminum back-surface-field (Al-BSF) with recombination rate of 200 to 600 cm/s. Currently, to reduce the high recombination rate of the Al-BSF and increase the field-effect passivation with negative charge, Al2O3 and silicon nitride (Si3N4) stacked films are mostly used on the back surface in commercial PERC cells. Moreover, the laser drilling process in PERC cells is complication. Therefore, in this work, screen-printed Al2O3 paste and ALD Al2O3 layer were adopted as the passivation layer and barrier layer, respectively. The parameters of the screen-printed Al2O3 paste, including the colloidal type of Al2O3 paste, the thickness of the emulsion, the gap of the screen, and the contact fraction between Al paste and silicon substrate, were presented. Next, the various thicknesses of the ALD Al2O3 passivation layers and effects of after ALD Al2O3 were investigated. At the same time, the effects of the Al2O3 stacked films formed by screen-printed and ALD techniques on the passivation layers of the PERC cells were addressed. The results indicated that the enhanced properties of the diffusion barrier can be demonstrated by increasing the viscosity in the Al2O3 paste when changing the colloidal types of the Al2O3 paste. When changing the thickness of the Al2O3 paste from 5 to 20 μm, it was found that the minimum thickness of the Al2O3 paste with around 10 μm was demonstrated for the thickness of the emulsion at 5 μm. When changing the gap of the screen ranged from 1.1 to 1.3, a thinner diffusion barrier layer can be achieved by a gap of 1.1. In the case of changing the different contact fraction, it was found that the better photovoltaic characteristics were presented by the contact fraction of 30 % combined with the gap of Al paste at 1.4 and the gap of the Ag paste at 1.6, a CE of 17.77 %. The photovoltaic characteristics of the PERC cells with screen-printed Al2O3 paste only can be enhanced by the combination of screen-printed and ALD deposited Al2O3 passivation layers. When changing the thickness of by ALD Al2O3 from 0 to 9 nm, it was found the thickness the best by ALD Al2O3 of 6 nm. When changing the after ALD Al2O3 of processing etched time from 0 to 15 sec, it was found the etched time the best of 5 sec. According to the optimum parameters, a CE of 18.0 % with an open-circuit voltage (Voc) of 641 mV, a short-circuit current density (Jsc) of 35.7 mA/cm2, a series resistance (Rs) of 1.6 Ω-cm2, and a fill factor (F.F.) of 80.01 % were demonstrated.

The performance of any photovoltaic device is determined by its ability to mitigate optical, recombination, and resistive energy losses. This thesis investigates new materials and nascent technologies to address these energy loss mechanisms in crystalline silicon solar cells. Optical losses, specifically the suppression of energy losses resulting from front surface reflection, are first analysed. The use of reactive ion etched black silicon texturing, a nano-scale surface texture, is assessed with respect to the two conventional texturing processes: isotexture and random pyramids. While nano-scale surface textures offer a means of almost eliminating front surface reflection, relatively poor internal optical properties (i.e. light trapping) compared to both conventional textures can compromise any optical gains realised on the front surface. It is also shown that enhanced recombination losses remains a barrier to the application of black silicon texturing to further improve high performance devices, though this will likely have less of an impact on multi-crystalline silicon cells where bulk recombination dominates. The suppression of recombination losses at surface defects by gallium oxide (Ga2O3), an alternative to aluminium oxide (Al2O3), is also investigated. It is demonstrated that, as in Al2O3, thin films of amorphous Ga2O3 can passivate surface defects through a direct reduction of recombination active defects and via the establishment of a high negative charge density. Further investigations demonstrate that Ga2O3 is applicable to random pyramid surfaces textures, and is compatible with plasma enhanced chemical vapour deposited silicon nitride (SiNx) capping for anti-reflection purposes. Indeed, the Ga2O3 / SiNx stack is shown to result in enhanced thermal stability and surface passivation properties comparable to state-of-the-art Al2O3 films. In addition, it is also shown that Ga2O3 can act as a Ga source in a laser doping process, as demonstrated by a proof-of-concept p-type laser doped partial rear contact solar cell with an efficiency of 19.2%. Finally, the resistive losses associated with metal / silicon contacts are addressed. It is demonstrated that a significant asymmetry in the work function of the electron and hole contact materials is sufficient to induce carrier selectivity without the need for heavy doping. This had recently been demonstrated for hole contacts with the high work function material molybdenum oxide. In this thesis specific attention is given to finding a suitable low work function material for the electron contact. Calcium, a common low work function electrode in organic electronic devices, is shown to act as a low resistance Ohmic contact to crystalline silicon without the need for heavy doping. Fabrication of n-type solar cells with partial rear calcium contacts resulted in a device efficiency of 20.3%, limited largely by recombination at the Ca / Si interface. This limitation to device efficiency is shown to be partially alleviated by the application of a passivating titania (TiOx) interlayer into the cell structure, resulting in an increase in device efficiency to 21.8% -- the highest reported efficiency for a TiOx-based heterojunction solar cell to date.