Heterostructure Growth via Cation Reaction for Surface Passivation in Inverted Perovskite Solar Cells

Surface passivation of inverted perovskite solar cells has advanced significantly, with molecular and heterostructure passivation strategies being the primary approaches. However, molecular passivation, the most widely used technique, faces challenges such as poor conformality, passivator penetration, and molecular degradation. Heterostructures, key to modern solid-state electronics and photonics, show considerable promise but are difficult to implement in halide perovskites, especially for p-i-n structures, due to issues such as random phase distribution and structural misalignment. In this study, we present a simple method for achieving optimal heterostructure passivation by growing an imidazolinium lead iodide (ImnPbI3) layer atop a 3D perovskite through a cation exchange reaction. Unlike traditional methods, which intercalate bulk organic cations into the perovskite to form non-oriented 2D passivation layers, we replace the formamidinium (FA) cations with imidazolinium (Imn) cations via a selective reaction with ethylenediamine (EDA). This approach preserves the original facet orientation, allowing for high-quality, oriented growth of the ImnPbI3 passivation layer. The resulting device achieves a power conversion efficiency (PCE) of 25.2%. Heterostructure growth is visualized using scanning electron microscopy (SEM), providing new insights into the passivation mechanisms of inverted perovskite solar cells.