Correlation between carrier recombination and valence band offset effect of graded Cu(In,Ga)Se2 solar cells

Abstract

Carrier recombination in Cu(In,Ga)Se2 (CIGS) solar cells is one of the critical factors determining cell performance loss. Additionally, heterointerface recombination is the most detrimental recombination pathway based on the Shockley–Read–Hall mechanism. Various methods have been applied to impede interface recombination, and the introduction of a valence band offset (ΔEV) produced by a homogeneous Cu-deficient layer (CDL) has been proved to be effective for improving cell efficiency. However, the relationship between ΔEV and recombination processes has not yet been fully clarified. In this work, through a Se interval irradiation process, ΔEV was incorporated into CIGS solar cells with bandgap grading so as to explore the correlation between the ΔEV effect and heterointerface recombination, which was demonstrated by both SCAPS-1D simulation and experiment. Moreover, illumination-dependent open-circuit voltage (Suns–Voc) and temperature-dependent open-circuit voltage (Voc–T) measurements were performed to quantitatively estimate the recombination rates at the interface, in the space-charge region (SCR), and in the quasi-neutral region (QNR), contributing to elaboration of the mechanism by which ΔEV serves as a hole barrier at the interface, thereby reducing heterointerface recombination and enhancing cell performance.