This study highlights an interface-engineering strategy aimed at simultaneously stabilizing nickel oxide (NiOx) sol-gel solutions and overcoming the intrinsic defects and charge transport limitations of NiOx. NiOx has been widely established as an efficient and stable hole transport layer in inverted perovskite solar cells, but sol-gel-based NiOx is susceptible to defect formation during thermal annealing, leading to non-uniform interfacial contact and limited charge extraction efficiency. To address these issues, ethylenediamine (EDA) chelation and γ-ray irradiation were integrated into the sol-gel NiOx process to modulate its chemical and electrical properties, followed by the introduction of a MeO-2PACz self-assembled monolayer, thereby improving interfacial ordering and hole extraction. EDA serves as a bidentate chelating ligand, stabilizing metal cations and suppressing premature hydrolysis, thereby modulating the sol-gel chemistry and surface coordination environment of NiOx and generating an ─OH-rich surface. Subsequently, γ-ray irradiation further modulates the oxidation state of NiOx within the EDA-modified chemical environment, leading to enhanced p-type conductivity. The resulting surface provides favorable anchoring sites for MeO-2PACz, promoting improved molecular ordering and interfacial energy-level alignment. As a result, the EDA-treated γ-NiOx/MeO-2PACz composite HTL enables efficient hole extraction, achieving a power conversion efficiency of 24.06% with enhanced operational stability.
Chae et al. (Wed,) studied this question.