Advance Supply of Ag and Ga-Se for Increased Backside Ga and Enhanced Cu(In,Ga)Se2 Solar Cell Efficiency

Abstract

Copper indium gallium selenide (CIGS) solar cells, known for their high conversion efficiency, are designed with a V-shaped bandgap grading approach. This is accomplished by adjusting the Ga/(Ga + In) (GGI) ratio across the absorber layer. However, several factors can contribute to the lower open-circuit voltage and fill factor of CIGS solar cells, including nonoptimal bandgap grading, incomplete or nonuniform absorber layers, poor crystal quality, bulk defects within the CIGS absorber, and high recombination at the CIGS/Mo interface on the back surface. In this study, we introduced a dual-modification method to alter the GGI profile without changing the Ga/In input and substrate temperature of the existing three-stage process using a pre-Ga-Se supply. Our results reveal that incorporating Ag can increase the size of the backside grains and directly affect the GGI shape, resulting in a more extensive grain-back contact morphology. This discovery highlights the potential of Ag as a valuable tool for achieving enhanced GGI backsides and consequently a larger open-circuit voltage (VOC). Moreover, it highlights Ag as an attractive option for the development of highly efficient CIGS solar cells. The resulting devices achieved a power conversion efficiency of 17.23% under simulated AM 1.5 illumination without any postdeposition treatment or antireflective coatings. © 2023 American Chemical Society.