Effects of CuIn1-xGaxSe2 thin film surface roughness in chemical bath deposition of CdS thin films

Abstract

Typical CuIn1-xGaxSe2 (CIGS) thin film solar cells on soda-lime glass (SLG) substrate consist of six different thin film layers; SLG/Mo/CIGS/CdS/i-ZnO/ZnO(Al)/Al-grids. In this work, the interface of CIGS/CdS film was modified by altering CIGS surface with various chemical solutions such as aqua regia, potassium hydroxide and alcoholic potassium hydroxide. The modified CIGS surface was investigated by FESEM and AFM in terms of morphology and RMS roughness, respectively. It was found that aqua regia could effectively alter the CIGS surface while the others could not visually change the surface. The J-V and external quantum efficiency (EQE) measurements showed that potassium hydroxide and alcoholic potassium hydroxide etchings resulted in lower solar cell performance than aqua regia etching when compared with the non-etched condition. The concentration and etching time using aqua regia were investigated. As a result, using 1:1 of aqua regia : deionized water at a few seconds of etching time could create an optimal CIGS surface roughness for the CIGS/CdS interface. This method was employed in the fabrication of the CIGS solar cells in order to improve its performance.