Theoretical analysis of minority carrier lifetime and Cd-free buffer layers on the CZTS based solar cell performances

Abstract

In this report, one dimensional simulation program (SCAPS-1D) has been used to study the crucial effect of minority carrier lifetime on Cu2ZnSnS4 based solar cells. The results have led to a strong correlation between the minority lifetime and the Cu2ZnSnS4 absorber thickness. Then, the modeling and investigation of Cu2ZnSnS4 based solar cells with graded Zn1-xMgxO and ZnO1-ySy buffer layers revealed that, these buffer layers could be an alternative to the CdS layer if the Mg and S compositions are suitably adjusted. In the case of Zn1-xMgxO buffer layer, the device with Zn0.75Mg0.25O shows the best efficiency and produces an improvement of 4.8%, whereas cells with ZnO1-ySy show an enhancement above 5% once the S composition is larger than 0.3. These performances have ascribed to the favorable band alignment at the buffer layers/Cu2ZnSnS4 interface, a strong electric field at the p-n junction and great transparency of these alternative buffer layers. The simulations have also showed a high potential barrier at the ZnO-intrinsic/alternative buffer layers interface which harms the electrons’ transport.