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© <2018>. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0, Interdigitated back contact technology is a promising candidate to be applied to thin crystalline silicon solar cells because of its simpler one-side interconnection while allowing a more flexible front surface treatment. This work explores the efficiency potential of IBC c-Si solar cells applied to thin c-Si substrates through 3D device simulations. In particular, we explore the impact of substrate thickness and front surface recombination velocity on cell performance with special attention to the different behavior in carrier collection of two different rear-surface doping structures. Firstly, the model is validated by comparing simulation results to a fabricated device on 280¿µm-thick substrates with stripe-like p+ and n+ diffusions. It is revealed that efficiencies of 16–17% are reachable for substrates on the 10–15¿µm range without changing the technology developed for thick ones. Next, the rear doping structure is modified leading to doped regions just under the metal contacts. This type of structure is expected in solar cells where high-temperature diffusions are replaced by point-like laser doped contacts, which is a feasible alternative to be applied to thin substrates. Simulation results show that diffusion length requirements for those locally-doped structures are more demanding due to the reduction of emitter regions. As a result, very well passivated front and rear surfaces are required to maintain short-circuit current densities to reasonable values. Finally, for both structures open-circuit voltage is kept almost constant with reduced thickness, despite the strong reduction in short-circuit current. Simulations show a reduction of dark saturation current density with substrate thinning due to the redistribution of dark current densities that flow parallel to the device surface., Peer Reviewed, Postprint (author's final draft)

Black silicon (b-Si) reduces drastically light reflectance in the front side of c-Si solar cells to values near zero for the whole absorbed solar spectrum. In this work, we apply 2D and 3D simulations to explore the efficiency limits of interdigitated back-contacted c-Si(n) solar cells with line or point contacts respectively, using ALD Al2O3 passivated b-Si in the front surface. Realistic physical and technological parameters involved in a conventional oven-based fabrication process are considered in the simulations, especially those related to surface recombination on the b-Si as well as high doped p+/n+ strip regions. One important issue is the temporal stability of surface passivation on b-Si surfaces. In this work experimental long-term b-Si surface passivation data after two years and its impact on cell performance are studied. Simulations demonstrate initial and final photovoltaic efficiencies over 24.6% and 23.2% respectively for an emitter coverage of 80% independently of the cell contact strategy. A photocurrent loss about 1.3 mA/cm2 occurs when surface recombination velocity at the b-Si surfaces degrades from 6 cm/s to a final value of 28 cm/s., Postprint (author's final draft)

Reducing the wafer thickness for c-Si solar cell fabrication is an effective approach for cost-savings. Interdigitated Back Contacts (IBC) technology is a promising candidate to be applied to thin c-Si substrates due to its potential to facilitate thin device processing: thin c-Si solar cell could be processed attached to a glass with its rear surface, where all the contacts are to be defined, still accessible. The understanding of thin IBC c-Si solar cell performance has great significance in guiding the design of such devices. In this work, we explore the performance of thin IBC c-Si solar cells by both 3D TCAD device simulations and experimental fabrication based on conventional technology developed in our research group. On one hand, an optical model is proposed using 2D ray tracing method whose results are applied to 3D ATLAS TCAD simulator which is used to simulate the electrical performance of the devices. As a result, efficiencies in the range of 20 % are expected for substrates of 10-20 µm without changing our technology. On the other hand, a ~30 µm IBC solar cell is fabricated by thinning down a previously developed IBC c-Si solar cell on conventional thick high quality substrates demonstrating a 12.1% of efficiency. The front surface passivation provided by Al2O3 is deduced by comparing with the simulation results revealing a front surface recombination velocity of about 1500 cm/s., Peer Reviewed, Postprint (published version)

In this work we describe a baseline fabrication process of interdigitated-back-contact c-Si(p) solar cells, which combines conventional diffusion oven stages to define base p+ and emitter n+ regions at the backside, with front surface passivation using atomic layer deposited Al2O3 films on textured surfaces with random pyramids. Very low reflectance with outstanding surface recombination velocity values around 3 cm/s are achieved in our precursors. Fabricated solar cells reach efficiencies up to 20.3% (AM1.5G 1 kW/m2, T=25°C), with short circuit density Jsc, open circuit voltage Voc and fill factor FF of 40.6 mA/cm2, 648 mV and 77.2% respectively., Postprint (published version)

In this work we study the fabrication and characterization of boron diffused emitters using FZ c-Si(n) substrates. Emitter surface was passivated with Al2O3(25 nm thick) layers deposited by thermal atomic layer deposition ALD technique. This study covers a broad emitter sheet resistance Rsh range from 20 to 250 Ω/sq using both polished and textured wafers. Emitter electrical quality was tested by means of lifetime measurements using quasi-stationary photoconductance QSS-PC method. Dark saturation emitter current densities Joe's were extracted from lifetime measurements resulting in Joe's values ranging from 10 to 150 fA/cm2 depending on Rsh. These results are in the-state-of-the-art in boron emitter passivation., Peer Reviewed, Postprint (published version)

El proyecto tiene como principal objetivo la fabricación de células solares de alta eficiencia (>20%) en sustratos de silicio monocristalino tipo P con estructura LFC-PERC., [ANGLÈS] The goal of this project is the fabrication in clean room of high efficiency (beyond 20%) solar cells with PERC-LFC structure. This document describes exhaustively the fabrication process of three batches of devices (each one slightly modified). Then their voltage-current characteristic and external quantum efficiency are measured, and the results are related to their particular fabrication process, showing the differences between batches. This allows a better understanding of the whole process., [CASTELLÀ] El objetivo de este proyecto es la fabricación de células solares de alta eficiencia (eficiencia de conversión superior al 20%) tipo PERC-LFC en sala blanca. En él se describe exhaustivamente el proceso de fabricación de tres remesas de dispositivos (con sutiles modificaciones entre ellos). Por último se caracterizan mediante medidas de la característica corriente-tensión y de eficiencia cuántica, y se relacionan los resultados con las variaciones empleadas en cada caso., [CATALÀ] L'objectiu d'aquest projecte és la fabricació a la sala blanca de cèl·lules solars d'alta eficiència (eficiència de conversió superior al 20%) amb estructura PERC-LFC. Es descriuen exhaustivament els procesos de fabricació de tres tongades de dispositius (amb subtils modificacions entre elles). Posteriorment es caracteritzen mitjançant mesures de la característica corrent-tensió i d'eficiència cuàntica externa, i es relacionen els resultats amb les variacions empleades en cada cas.

English: he goal of this project is the fabrication of a two axis sun sensor for the attitude control of the IntaMicroSat satellite. This sensor should detect the position of the sun with high accuracy (±1 º) and at an angle FOV (Field Of Vision) ± 60 º. It must present low size and weight. The manufacture of this sensor, named vectorsol de cuatro cuadrantes, is made entirely in the clean room available to the Department of Electronic Engineering of the Polytechnic University of Catalonia. The final results show the high accuracy achieved (the error is of 0.15°) and high yield resulting of the process., Castellano: El objetivo de este proyecto es la fabricación de un sensor solar en dos ejes para su integración en el control de actitud del satélite IntaMicroSat. Este sensor debe detectar la posición del sol con una precisión elevada (±1º) y con un ángulo FOV (Field Of Vision) de ±60º. Asimismo, debe presentar bajo consumo, tamaño y peso. La fabricación de este sensor, bautizado como vectorsol de cuatro cuadrantes, se ha realizado íntegramente en la sala blanca de que dispone el Departamento de Ingeniería Electrónica de la Universidad Politécnica de Cataluña. En cuanto a los resultados finales obtenidos, cabe destacar la elevada precisión conseguida (que tiene un error de 0.15º) y el elevado yield (tasa de dispositivos funcionales respecto al total)., Català: L'objectiu d'aquest projecte és la fabricació d'un sensor solar en dos eixos per a la seva integració en el control d'actitud del satèl.lit IntaMicroSat. Aquest sensor ha de detectar la posició del sol amb una precisió elevada (±1º) y amb un angle FOV (Field Of Vision) de ±60º. Tanmateix, ha de presentar baix consum, pes i mides reduïdes. La fabricació d'aquest sensor, batejat com a vectorsol de cuatre cuadrants, s'ha realitzat íntegrament a la sala blanca del Departament d'Enginyeria Electrònica de la Universitat Politècnica de Catalunya. En quant als resultats finals obtinguts, cal destacar l'elevada precisió conseguida (amb un error de 0,15º) i el gran yield (taxa de dispositius funcionals respecte al total).

English: The goal of this project is the fabrication of a two axis sun sensor for the attitude control of the SeoSat satellite. This sensor should detect the position of the sun with high accuracy and at an angle FOV (Field Of Vision) ±60 º. It must present low size and weight. This sensor, named multivectorsol, is manufactured entirely in the clean room available to the Department of Electronic Engineering of the Polytechnic University of Catalonia. The final results show the high accuracy achieved (the error is of 0.05°) and high yield resulting of the process., Castellano: El objetivo de este proyecto es la fabricación de un sensor solar de alta precisión en dos ejes para su integración en el control de actitud del satélite SeoSat. Este sensor debe detectar la posición del sol con una precisión elevada y con un ángulo FOV (Field Of Vision) de ±60º. Asimismo, debe presentar bajo consumo, tamaño y peso. La fabricación de este sensor, bautizado como multivectorsol, se ha realizado íntegramente en la sala blanca de que dispone el Departamento de Ingeniería Electrónica de la Universidad Politécnica de Cataluña. En cuanto a los resultados finales obtenidos, cabe destacar la elevada precisión conseguida (el error en la medida es inferior a 0.05º) y el elevado yield (tasa de dispositivos funcionales respecto al total)., Català: L'objectiu d'aquest projecte és la fabricació d'un sensor solar d'alta precisió en dos eixos per a la seva integració en el control d'actitud del satèl.lit SeoSat. Aquest sensor ha de detectar la posició del sol amb una precisió elevada y amb un angle FOV (Field Of Vision) de ±60º. Tanmateix, ha de presentar baix consum, pes i mides reduïdes. La fabricació d'aquest sensor, batejat com a multivectorsol, s'ha realitzat íntegrament a la sala blanca del Departament d'Enginyeria Electrònica de la Universitat Politècnica de Catalunya. En quant als resultats finals obtinguts, cal destacar l'elevada precisió conseguida (l'error es inferior a 0.05º) i el gran yield (taxa de dispositius funcionals respecte al total).

In this work we study the fabrication and characterization of boron diffused emitters using FZ c-Si(n) substrates. Emitter surface was passivated with Al2O3(25 nm thick) layers deposited by thermal atomic layer deposition ALD technique. This study covers a broad emitter sheet resistance Rsh range from 20 to 250 Ω/sq using both polished and textured wafers. Emitter electrical quality was tested by means of lifetime measurements using quasi-stationary photoconductance QSS-PC method. Dark saturation emitter current densities Joe's were extracted from lifetime measurements resulting in Joe's values ranging from 10 to 150 fA/cm2 depending on Rsh. These results are in the-state-of-the-art in boron emitter passivation., Peer Reviewed, Postprint (published version)