Simulation analysis of Cd-free Cu(In,Ga)Se2 solar cells with novel BiOX (X=Cl, Br) buffer layers

Abstract

Nowadays, cadmium sulfide (CdS) or zinc oxysulfide (Zn(O,S)) are the traditional buffer layer of Cu(In,Ga)Se2 (CIGS) solar cells. However, these buffer layers contain several disadvantages, such as the complicated synthesis problem and heavy metal toxicity. To solve the above problems, the potential of Bi-based (BiOX: X = Cl, Br) materials employed as buffer layers for efficient CIGS solar cells are investigated by using SCAPS simulation software in this contribution. It can be found that all BiOX materials fabricated from a soft liquid deposition process possess 2D nanosheet structures. A comparison of 2D nanosheet size reveals that BiOBr can form easily compared with BiOCl under the same growth conditions. Simultaneously, DRS and XPS determine the energy band distribution of BiOX materials. Further investigations on the simulated device performance suggest that conversion efficiency of the BiOBr sample is maximum, which is close to that of CdS and much larger than the BiOCl sample, mostly owning to the increased JSC and FF. The reason for this results is that the energy band distribution of BiOBr is similar to that of CdS buffer layer. It also indicates that BiOBr has the potential to serve as a buffer layer material for solar cells.