Effect of the front surface field (a-Si:H) on the spectral response of thin films heterojunctions solar cells

Abstract

The present paper accounts for a simulation study carried out to determine and optimize the effect of the high---low junction emitter front surface field (FSF) of thin heterojunction solar cell $$\text {n}^{+}$$n+(a-Si: H)/n(SiGe)/p(Si)). A theoretical model describing the behavior of heterojunction $$\text {n}^{+}$$n+---n---p type solar cells has been proposed. Besides, the expression of the photovoltaic equations allowing for the obtention of the optimal quantum efficiency of the solar cells based on the suggested model has been given. The effects of the a-Si:H-layer thickness and Ge fraction are discussed, using the computed results. The main role of an FSF layer is to reduce the effect of front surface recombination and the enhancement of light-generated free carriers' collection. This is primarily responsible for the increase of the spectral response compared with the conventional solar cell. This is achieved by the drastic reduction of the effective recombination at the emitter upper boundary and the optimum value of $$\text {n}^{+}$$n+ layer thicknesses (a-Si:H) is about 2 nm.