Numerical analysis on effects of experimental Ga Grading on Cu(In,Ga)Se2 solar cell performance

The Ga gradient optimization is an important subject in the studies of Cu(In _1-x,Ga _x)Se ₂ (CIGS) solar cells, and numerical simulation has been demonstrated as an informative approach to investigate the effects of Ga grading profiles on device performance. The Ga grading profiles modeled in previous studies are mostly based on simplified piecewise linear structures, few simulation works treat the real experimental Ga gradient directly. In this paper, we present a theoretical method that allows for the inclusion of experimentally obtained Ga grading profiles as a modeling input, and from that compare the modeling results of several CIGS samples with experimental device data. It is found that the non-uniformity of carrier mobility needs to be considered in the model for cells having different grain sizes across the whole CIGS film. Besides the effects of the Ga gradient profile, additional factors including crystalline qualities should be considered to obtain modeling results consistent with experimental observation. The modeling approach implemented in this work improves numerical models to attain better predictability of the simulation, and provides deeper insights into the effects of Ga gradient profiles on real CIGS solar cells, which is helpful for extracting more information from interpreting the experimental data.