Influence of Inorganic NiOx Hole Transport Layer on the Growth of CsBi3I10 Perovskite Films for Photovoltaic Applications

Abstract Lead (Pb)‐free bismuth (Bi) halide perovskites are promising alternatives to Pb‐based ones for the fabrication of perovskite solar cells (PSCs). However, the energy‐level mismatch at the interface between Bi perovskite (CsBi 3 I 10 ;CBI) and the charge carrier transport layer limits the performance of the PSCs. Here, spray pyrolysis processed nickel oxide (sp‐NiO x ) is reported as a hole transport layer (HTL) for CBI‐based inverted planar PSCs. Influence of inorganic NiO x HTL is systematically studied on the structural and morphological properties of the CBI perovskite layer growth. The CBI perovskite deposited on top of the sp‐NiO x exhibits improved crystallinity. The fabricated sp‐NiO x layer also exhibits favorable optical and electrical properties. The deep valence band (−5.4 eV) of the sp‐NiO x HTL is able to reduce the energy‐level mismatch up to 0.3 eV at the interface with the CBI layer. The PSCs fabricated with sp‐NiO x as HTL also exhibits a power conversion efficiency (PCE) of 0.72%, with a short‐circuit current density of 2.89 mA cm −2 . The sp‐NiO x HTL based device maintains 85% of its initial PCE value even after 100 h of light soaking. This work highlights the importance of having a suitable HTL along with appropriate interface engineering for the Bi halide photovoltaic devices.