Improved photocurrent in Cu(In,Ga)Se2 solar cells: From 20.8% to 21.7% efficiency

New processing developments in the Cu(In,Ga)Se₂ (CIGS)-based solar cell technology have enabled progress to the next level of best cell efficiencies exceeding 21%. This result was achieved by applying the alkali post-deposition treatment (PDT) to the CIGS film, which effects changes both in the bulk and on the surface of the film. Furthermore, we have found that these modifications affect the range of optimal CIGS growth parameters and the minimal thickness of the CdS buffer layer. Our first experiences with PDT lead to a 20.8% record device. Later optimizations in the composition profile and CdS buffer layer thickness enabled us to increase the photocurrent density with only a slight loss in open-circuit voltage and unchanged fill factor, resulting in the current world record of 21.7% efficiency. This contribution presents measurements, simulations, and a discussion of the photocurrent increase.