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)Se2 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 Cu x Se 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. Combined with surface aging control, simultaneously deposited Ga and Cu, and annealing process, high‐efficient CuGaSe2 solar cells can be fabricated without using KCN treatment and high Se flux for the first time. Based on the aforementioned three methods developed in this work, defects in the device and interfacial recombination has been significantly reduced.