Unraveling the modification effect at NiO_x/perovskite interfaces for efficient and stable inverted perovskite solar cells

Due to low costs and high light transmittance, solution-processed NiO_x nanocrystals as the hole transport layer (HTL) for inverted perovskite solar cells (PSCs) have attracted great attention recently. Nevertheless, the intrinsic defects (Ni vacancies) in the NiO_x film and the I vacancies at the buried interface of the perovskite limit the performance of PSCs. Thus, in this work, iodine-substituted phenyl acids are used to modify the NiO_x/perovskite layer interface. Our results show that the acid functional groups have strong coordination with Ni vacancies in the NiO_x film, giving rise to a high conductivity of NiO_x films and thereby an improved hole transport capacity. The para-iodine gives the molecule a larger dipole moment, leading to a better energy level alignment between NiO_x and the perovskite and thereby a favorable hole transfer through the NiO_x/perovskite interface. As a result, the PSC based on 4-iodophenylboronic acid yields a champion power conversion efficiency (PCE) of 22.91% and an improved fill factor of 86.18%. The non-encapsulated device maintains above 80% of its initial PCE after storing in N₂ for 3000 h, under heating at 60 °C for 1000 h and in air with a relative humidity (RH) of 50-70% for 1000 h.