Surface Sulfuration of NiO Boosts the Performance of Inverted Perovskite Solar Cells

As one of the most promising hole-transporting materials for perovskite solar cells (PSC), NiO is widely used in the inverted p–i–n cell structure due to its high stability, decent hole conductivity, and easy processability for hysteresis-free cells. However, the efficiency of NiO-based PSCs is still low, due largely to the poor perovskite/NiO interface. Herein, a sulfur-doping strategy to modify NiO surface via ion exchange reaction by a simple and scalable chemical bath deposition technique is introduced, which greatly improves the photovoltaic (PV) performance of the derived devices. A systematic investigation is shown where sulfur doping leads to favorable interfacial energetics with a reduced V_oc loss. Sulfur doping at the interface also improves the contact between NiO and perovksite and facilitates the formation of high-quality perovskite films. Carrier dynamics studies demonstrate reduced defect states and trap-assisted recombination with sulfur doping, which promote the PV performance of the devices. These merits contribute concurrently to low-loss charge transfer across the perovskite/NiO interface and facilitate charge transport through the perovskite films, leading to a high champion efficiency of 20.43% of the p–i–n structure solar cell devices.