Shallow B-implanted Emitters with Laser Overdoping from AlOx Passivating Layers

AbstractA simple process for the fabrication of selective emitter structures on n-PERT cells is investigated, using shallow Boron emitters obtained by ion implantation. By tuning the emitter doping process parameters, J0e values as low as 10 fA.cm-2 have been obtained with highly resistive profiles. Laser overdoping processes from AlOx passivating layers are tested on these profiles to locally increase the emitter conductivity and allow better contact properties. Through this process the emitter sheet resistance and doping profile may be locally controlled with a limited impact on the J0e values

TCO-free low-temperature p+ emitters for back-junction c-Si solar cells

In this work, we report on the fabrication and characterization of n-type c-Si solar cells whose p+ emitters are based on laser processed aluminum oxide/silicon carbide (Al2O3/SiCx) films. The p+ emitter is defined at the rear side of the cell and it consists of point-like laser-diffused p+ regions with a surface charge induced emitter in between based on the high negative charge located at the Al2O3/c-Si interface. These emitters are fabricated at low temperature (1000 nm) that reach the rear surface of the cell resulting in an excellent back reflector. We fabricated solar cells with distance between p+ regions or pitch ranging from 200 to 350 µm with a front surface based on silicon heterojunction technology. Best efficiency (18.1%) is obtained for a pitch of 250 µm as a consequence of the trade-off between Voc and FF values.Peer ReviewedPostprint (published version

Développement de cellules photovoltaïques à hétérojonctions silicium et contacts en face arrière

Cette thèse explore une nouvelle voie pour améliorer le rendement des cellules solaires à base de silicium cristallin. Cette nouvelle approche utilise la technologie des hétérojonctions a-Si:H / c-Si (Si-HJ) appliquée sur des structures à contacts en face arrière interdigités (IBC). Les dispositifs combinant ces deux technologies (Si-HJ IBC) peuvent théoriquement atteindre des rendements supérieurs à 25 % avec un procédé entièrement à basse température (? 200°C). Dans cette étude, les cellules solaires sont fabriquées sur des substrats c-Si de type n de 25 cm2. Les procédés de fabrication utilisés sont potentiellement adaptés à une industrialisation (PECVD, pulvérisation, sérigraphie, LASER, masques métalliques). Des couches a-Si:H ultra-minces (entre 5 et 30 nm) dopées sont utilisées pour réaliser les zones démetteur et de BSF en face arrière des cellules solaires. Des matériaux a-Si:H, a-SiNx:H, a-SiCx:H et ITO sont également étudiés pour des applications comme couches de passivation et / ou anti-reflet. Pour fabriquer les cellules Si-HJ IBC, différentes couches sont localisées à laide de masques métalliques structurés et alignés mécaniquement. Le plus haut rendement atteint par les dispositifs Si-HJ IBC réalisés atteint ici 12.7%. Il sagit, à notre connaissance, du meilleur résultat obtenu au niveau mondial par ce genre de structures sur du c-Si de type n. Les performances des dispositifs expérimentaux restent principalement limitées par une faible valeur de FF. Des modélisations 2D des structures Si-HJ IBC montrent que la conception de lémetteur et de son contact en face arrière peut entraîner des limitations à la fois sur ce FF mais également sur le Jcc. Ces phénomènes peuvent être attribués à une résistance série « distribuée » importante sur les cellules Si-HJ IBC. Différentes perspectives damélioration sont proposées, au niveau de la géométrie de la structure principalement. Ces optimisations devraient permettre à la fois une simplification des cellules Si-HJ IBC ainsi que laugmentation de leur rendement

Probing hidden conduction mechanisms in diced silicon solar cells by low frequency noise analysis

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Parasitic oscillation in the low-frequency noise characterization of solar cells

International audienceThe analysis of low-frequency noise in solar cells is a very useful tool for defect characterization or understanding of fluctuation mechanisms in photodiodes. This type of noise characterization can however be limited by the presence of an undesired peak in the frequency spectra, caused by an oscillation in the measured current. It is shown in this work that this phenomenon originates in the interaction between the noise measurement system and the test structures of the solar cells, which usually introduce a high parasitic capacitance. Through experimental measurements, the link between the center frequency of the peak and the sensitivity of the noise measurement amplifier, as well as the solar cell surface area were explored. Finally, it is shown that, for characterization purposes, the oscillation peak could be pushed to higher frequencies by measuring smaller area cells or attenuated by choosing electrode shapes that enhance the device series resistance

Bifacial crystalline silicon homojunction cells contacted with highly resistive TCO layers

International audienceThis study explores the needed properties of Transparent Conductive Oxides (TCOs) for bifacial homojunctionsolar cells with potentially passivated contacts. TCO layers with different electrical and optical properties have been testedon both sides of n-type homojunction cells. The high lateral conductivity provided by the diffused emitter and back surfacefield (BSF) greatly reduces the constraints on TCO electrical properties in such structures. An understanding of the requiredproperties of TCO for advanced homojunction applications is given. Hence different O2-rich Indium Tin oxide (ITO) layersare analyzed optically and electrically before being implemented in homojunction solar cells to evaluate their influence onthe device performances. All in all moderately conductive TCOs are shown to be suitable for such applications, allowingbetter optical properties without inducing resistive losses in the devices

Développement de TCO sans Indium pour les cellules solaires silicium à contacts passivés

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TCO contacts for high efficiency c-Si solar cells: Influence of different annealing steps on the Si substrates and TCO layers properties

International audienceDistrict heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. Abstract Different Transparent Conductive Oxide (TCO) layers properties are evaluated after annealing steps at temperatures above 200°C, in order to study their potential use in crystalline silicon (c-Si) solar cells fabrication processes. While the conductivity of Indium Tin Oxide (ITO) layers obtained by magnetron sputtering (MS) is almost stable after annealing in air, Aluminum doped Zinc Oxide (AZO) layers deposited by Atomic Layer Deposition (ALD) need a controlled atmosphere to maintain high carrier densities and mobilities. During the annealing processes, contaminating atoms (such as Zn) diffuse into the c-Si bulk and may potentially decrease its quality. Thus, both the contamination of the c-Si bulk and the properties of the AZO layer have been analyzed. Abstract Different Transparent Conductive Oxide (TCO) layers properties are evaluated after annealing steps at temperatures above 200°C, in order to study their potential use in crystalline silicon (c-Si) solar cells fabrication processes. While the conductivity of Indium Tin Oxide (ITO) layers obtained by magnetron sputtering (MS) is almost stable after annealing in air, Aluminum doped Zinc Oxide (AZO) layers deposited by Atomic Layer Deposition (ALD) need a controlled atmosphere to maintain high carrier densities and mobilities. During the annealing processes, contaminating atoms (such as Zn) diffuse into the c-Si bulk and may potentially decrease its quality. Thus, both the contamination of the c-Si bulk and the properties of the AZO layer have been analyzed