Performance study of a graded band gap solar cell based on CZTS(SE)

The large-scale development of photovoltaic electrical energy is still conditional on lowering the cost of solar cells and increasing their efficiency. Since the realization of the first photovoltaic cell, several research works have been initiated to solve this problem, especially thin film solar cells. Thin film solar cells represent promising approaches for cutting production costs include the use of thin films solar cells. This generation's benefit is that they frequently employ semiconductor materials with direct band gaps, which have exceptionally high absorption coefficients. In this context, thin film solar cells based on a material (CZTS) play a role at low cost. CZTS (Cu2ZnSnS4) is a quaternary semiconductor of the I2-II-IV-VI4 type, it is composed of abundant materials. It is a new type of absorber for thin film solar cells. Copper-zinc-tin-sulfur (CZTS) is a semiconductor with excellent photovoltaic properties such as direct gap, high absorption coefficient, and has an optimal band energy highly desired in photovoltaic material. In addition, the cells using CZTS are non-toxic and inexpensive materials. Currently, several researches have been devoted to develop and improve the electrical characteristics (particularly efficiency) of CZTS solar cells which show a theoretical limit efficiency of 32.4 % Shockley Quisser, while the experimental efficiency is 14.9% In this paper, we propose a potential efficiency Cu2ZnSn(S,Se)/CdS (CZTS) solar cell design based on graded band-gap that can offer the benefits of improved absorption behavior and reduced recombination effects. Moreover, our approach is based on analytical modeling to determine the optimal band gap profile of the absorber layer of the CZTS material to improve the photovoltaic conversion efficiency. The results of this study show that the use of a graded layer shows a decrease the recombination rate which leads to an increase in current from 22.16 mA/cm2 (for a standard CZTS cell) to 30 mA/cm2 (for a graded cell) and by therefore an improvement in efficiency from 10.9 % to 15.25 %