Self-doping synthesis of trivalent NiO as a hole transport layer for high fill factor and efficient inverted perovskite solar cells.

Nickel oxide (NiOx) as a hole transport layer has been vastly investigated in perovskite solar cells (PSCs) due to the nature of p-type doping, highly transparent materials, and deep-lying valence bands. In this paper, a new phase based on trivalent Ni2O3 is synthesized by low temperature solution processing of mixed nickel (acetate/nitrate). In comparison, high-temperature solution-processing of divalent NiOx resulted in novel Ni2O3 thin films that display better consistency and superior energy compatibility with perovskite thin films. In this respect, high-performance perovskite solar cells are efficiently produced utilizing MA0.85FA0.15PbI0.9Cl0.1 perovskite with a power conversion efficiency (PCE) reaching 17.89% and negligible hysteresis comparable to 14.37% for NiOx. The Ni2O3-based PSCs reported the highest fill factor (FF) (82.66%) compared to that of divalent NiOx (67.53%). Different characterization studies and analyses supply proof of improved film quality, increased transport and extraction of charges, and suppressed charge recombination. Meanwhile, the device exhibits low hysteresis compared to sol-gel-processed NiOx.