Impact of Mo barrier layer on the formation of MoSe2 in Cu(In,Ga)Se2 solar cells

Abstract

In this study, we investigated the impact of a Mo barrier layer (Mob) on the formation of MoSe2, as it relates to the performance of Cu(In,Ga)Se2 (CIGS) thin film solar cells with a structure of glass/Mo/Mob/CIGS/CdS/i-ZnO/ZnO:Al/Al. Experiments show that an increase in the thickness of Mob led to a significant decrease in the thickness of MoSe2 as well as a slight reduction in the thickness of the CIGS absorber layer following selenization. This can be attributed to the fact that the Na content in the CIGS absorber increased with an increase in the thickness of the Mob. Higher Na content in the absorber layer promoted the formation of Na2Sex at grain boundaries during selenization, thereby reducing the grain boundary diffusion of Se, which retarded the growth of excess MoSe2. Furthermore, the crystallinity of the absorber layer was improved when specific quantities of Na were included, which resulted in a relatively dense absorber layer of reduced thickness. Increasing the thickness of Mob also led to a more homogeneous distribution of elemental Ga throughout the absorber layer. Under optimal conditions (i.e., Mob = 20 nm), the thickness of MoSe2 was reduced from 819 nm to 220 nm, and device efficiency was increased from 4.9% to 10.03%.