Potassium-Doped Nickel Oxide as the Hole Transport Layer for Efficient and Stable Inverted Perovskite Solar Cells

Organic/inorganic hybrid perovskites have received a great deal of attention in solar energy harvest due to their high absorbance in the visible range, long carrier diffusion length, and solution processability. It is extremely important to develop high-quality hole transport layer (HTL) to replace PEDOT:PSS for fabricating inverted perovskite solar cells (PSCs) with high power conversion efficiency (PCE) and device stability. Upon this consideration, we proposed potassium (K)-doped nickel oxide (NiO_x) compact layer via the sol–gel process to improve the conductivity and to modify its work function. Inverted PSCs with the configuration of FTO/K:NiO_x/Cs_0.05FA_0.81­MA_0.14Pb­(I_0.85­Br_0.15)₃/TBABF₄+PCBM/TIPD/Ag were fabricated and evaluated. We found that the device based on 3% K-doped NiO_x showed the best performance with an optimized PCE of 17.05% and a high fill factor of 74%, and it retained about 80% of initial PCE value after 35 days storage. Our results provide a simple and effective approach to fabricate inverted PSCs with high efficiency and long-term stability for future production.