Improvement of the energy conversion efficiency of Cu(In,Ga)Se2 solar cells using an additional Zn(S,O) buffer

Abstract

CuInGaSe2 (CIGS) solar cells were prepared with two different buffer structures. Sample A had a single, thin CdS buffer, ~25nm in thickness, and Sample B had a very thin CdS buffer (<5nm thickness) with an additional Zn(S,O) buffer layer. The CIGS and CdS layers in these samples were prepared using a 3-step co-evaporation method and chemical bath deposition, respectively, whereas the additional Zn(S,O) buffer and boron (B)-doped ZnO window layer were prepared by metal organic chemical vapor deposition. The current–voltage curves, quantum efficiency, depth profile by secondary ion mass spectrometry, and transmission electron microscopy images of both samples were analyzed. Sample B showed greater open circuit voltage than Sample A, whereas the short circuit current of Sample B was less than that of Sample A. Even though the energy conversion efficiency is not markedly improved compared to the highest recorded value of each sample, it was quite obvious throughout this experiment that the additional buffer cells had higher reliability and homogeneous properties than CdS buffer cells.