Over 11% Efficient CuGaSe2 Solar Cells Without Using KCN Treatment

CuGaSe2 (CGS) has a bandgap energy of 1.68 eV and is theoretically very suitable to be in tandem with silicon or Cu(In,Ga)Se-2 solar cells. However, due to the high quantity of surface defects, high-performance CGS usually relies on a KCN surface treatment, which is a high-toxic process and restricts its further development. Herein, by reducing the exposure time to air of the CGS layer as far as possible and developing a new absorber growth procedure to reduce the surface CuxSe generation, grain size is successfully increased and interface recombination is reduced without the use of KCN. Combined with a simple annealing process, the defect concentration is successfully decreased and the depletion width is broadened dramatically and the power conversion efficiency is promoted to 11.05% without any traditionally used KCN treatment. This work provides a nontoxic and low-pollution way to fabricate high-efficient CGS solar cells.