Design of thin film solar cells based on a unified simple analytical model

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Armando Acevedo Luna
Roberto Bernal Correa
Jorge Montes Monsalve
Arturo Morales Acevedo

Abstract

Polycrystalline thin film solar cells made with absorber materials such as CdTe, CIGS, CZTS and metalorganic halides (perovskites) are currently important alternatives for the silicon solar cell technology, which still dominates the photovoltaic market. Then, it is important to have tools which can be used to design this kind of solar cells. For this purpose, we have developed a unified simple analytical model that can be applied to thin film solar cells. The model is based on the basic physics of hetero-junction devices, but it takes into consideration that the space charge region can extend along the major part of the cell length, particularly for very thin cells, causing important effects that typically are not observed in conventional junction devices. Photo-generated carriers are collected by electric field-drift instead of diffusion, and simultaneously strong recombination at this region may dominate the electrical I–V characteristic of the cell. Since the space-charge region width varies with the applied voltage, the illumination current density and the saturation dark current density are no longer independent of the voltage as is assumed for conventional solar cells. When the model is applied to CIS and CdTe solar cells as examples, it is found that it is possible to design very thin film solar cells (absorber less than 1 ?m thick) with high efficiencies, whenever the recombination velocity at the back surface becomes small (102 cm/s), instead of the high
recombination velocities present at ohmic contacts (107 cm/s). This fact implies the cost reduction of thin film solar cells by reducing absorber material thickness, and therefore it poses a challenge to develop deposition methods for very thin CdTe and CIGS absorber materials without pinholes, so that improved efficiencies are obtained when the surface recombination velocity is made small at the back by having a p+ or an electron blocking region before the ohmic contact. This result also explains the high efficiencies achieved by very thin perovskite solar cells.

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How to Cite
Luna, A. A., Correa, R. B., Monsalve, J. M., & Acevedo, A. M. (2019). Design of thin film solar cells based on a unified simple analytical model. Journal of Applied Research and Technology, 15(6). https://doi.org/10.1016/j.jart.2017.08.002
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Articles
Author Biographies

Armando Acevedo Luna

Centro de Investigación y de Estudios Avanzados del IPN, Electrical Engineering Department, Avenida IPN # 2508, 07360 Mexico, D.F., Mexico

Roberto Bernal Correa

Grupo DEMA, Facultad de Ciencias e Ingeniería, Universidad del Sinú, Montería, Colombia

Jorge Montes Monsalve

Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Colombia, Manizales, Colombia

Arturo Morales Acevedo

Centro de Investigación y de Estudios Avanzados del IPN, Electrical Engineering Department, Avenida IPN # 2508, 07360 Mexico, D.F., Mexico