Pristine inorganic nickel oxide as desirable hole transporting material for efficient quasi two-dimensional perovskite solar cells

The performance of quasi two-dimensional (Q-2D) perovskite solar cells (PSCs) prepared by hot-casting method is far from satisfactory owing to the inefficient charge transfer inside the film caused by undesirable underlying surface, in which hole transporting material (HTM) plays a critical role in achieving a stable and high performance p-i-n structured Q-2D PSCs. Herein, pristine nickel oxide (NiOx) is prepared by sol-gel method as a desirable HTM to fabricate p-i-n structured Q-2D PSCs. The formation of high-quality perovskite films with less defects and higher crystallinity can be promoted by the NiOx layer with desired wetting surface. Importantly, the NiOx HTM possesses a better energy-level match with post-deposited perovskite film, which largely boosts up the hole extraction efficiency. Consequently, the champion device achieves a remarkable power conversion efficiency (PCE) of 14.85%, which is the best result for inorganic HTM based Q-2D PSCs so far. Furthermore, compared with conventional organic polymer HTM, NiOx HTM possesses better chemical stability and more competitive prices. This work reveals that inorganic HTM with ideal wetting surface could be a superb choice to release the power of Q-2D perovskites for achieving ideal photovoltaic performance.