Formation of Ga double grading in submicron Cu(In,Ga)Se2 solar cells by pre-depositing a CuGaSe2 layer

Abstract

It is well-established knowledge that the formation of a V-shape Ga double grading along the thickness direction of a Cu(In,Ga)Se₂ (CIGS) absorber is beneficial and critical for highly efficient CIGS thin film solar cells. However, when the thickness of the absorber is reduced from the normal value to a submicron level value, the formation of such a Ga double grading becomes very difficult due to rapid element inter-diffusion. In this work, a novel growth route that introduces a pre-deposited CuGaSe₂ (CGS) layer at the beginning of the traditional three-stage co-evaporation method is developed to successfully form the Ga double grading in submicron CIGS. It has been demonstrated that the pre-deposited CGS layer can not only result in the formation of a steep Ga back grading but also improve the performance of the submicron CIGS solar cells. As a result, a submicron CIGS solar cell with over 15% conversion efficiency without anti-reflective coating (ARC) has been obtained after a suitable Ga double grading was created in the submicron thick absorber.