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 NiOx 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 NiOx 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 NiOx/perovskite layer interface. Our results show that the acid functional groups have strong coordination with Ni vacancies in the NiOx 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 NiOx and the perovskite and thereby a favorable hole transfer through the NiOx/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 N-2 for 3000 h, under heating at 60 C-degrees for 1000 h and in air with a relative humidity (RH) of 50-70% for 1000 h.