Boosting efficiency and stability with KBr interface modification for NiOx-based inverted perovskite solar cells

NiOx-based inverted structure perovskite devices possess advantages in the application of single junction and tandem solar cells. However, energy loss and instability originating from interface defects commonly result in inferior device performance. Herein, Potassium Bromide (KBr), as a buffer layer, was inserted between the perovskite and NiOx hole transport layer to modify the interface. The valence band maximum of NiOx improved to −5.37 eV which matches better with perovskite. The lifetime of hot carriers and intrinsic charge recombination revealed by Femtosecond transient absorption spectroscopy (fs-TAS) confirm that KBr modification can facilitate charge separation. Benefiting from the improvement of perovskite quality which results from K+ diffusion and enhanced charge transport, the power conversion efficiency (PCE) of the modified device reaches up to 19.21%, whereas the pristine is 17.56%. Meanwhile, the air stability of the unencapsulated device also improved dramatically, which maintains 80% of its initial PCE after 1100 h high humidity storage. This work unambiguous reveals the mechanism of perovskite/NiOx interface modification and provides a facile and effective strategy for interface optimization.