Regulation of crystallization by Introducing a multistage growth template affords efficient and stable inverted perovskite solar cells†

Abstract

The non-homogeneity of nickel oxide (NiO_x) nanoparticles (NPs) and the problematic interlayer interconnectivity in perovskite films are the current major bottlenecks for the further development of corresponding perovskite solar cells (PVSCs). Herein, a multistage growth template strategy is proposed to successfully ameliorate the crystallization kinetics of NiO_x NPs and perovskite films by modulating the intermolecular forces in nickel precursor solutions and the interfacial interactions of NiO_x/perovskites, respectively. Incorporated multifunctional imidazole tetrafluoroborate ([C_nMIM]BF₄) ionic liquids (ILs) can initially serve as a soft template for NiO_x growth, and altering the alkyl chain length forms NiO_x NPs with controllable sizes and tunable electronic structures. Meanwhile, the excellent solution dispersibility of IL-optimized NiO_x due to the electrostatic and steric-hindrance effects allows for good printability. Particularly, interface adherent ILs can subsequently regulate the Gibbs free-energy of perovskite nucleation and provide growth sites to assist high-quality crystallization for obtaining a homogeneous perovskite film with excellent interfacial interconnectivity. As a result, unencapsulated PVSCs display an impressive efficiency of 25.73% and superior stability, retaining over 80% of initial efficiencies after 800 h of storage in N₂ at 85 °C or 1400 h of aging in air with 40–50% relative humidity.