Synergistic Interface Optimization of Inverted Methylamine-Free Perovskite Solar Cells: A Study of Experiments, Calculations, and Numerical Simulations

The power conversion efficiencies (PCEs) of inverted methylammonium (MA)-free perovskite solar cells (PSCs) have yet to match those of their tricationic counterparts and conventional PSCs, due in part to suboptimal carrier transport, the inadequate morphology of hole transport layers (HTLs), and the inferior crystallinity of MA-free perovskite films. Herein, we address these challenges by introducing a nickel oxide (NiOx) film as a nucleation layer to facilitate the formation of a dense and uniform self-assembled monolayer of 2-(3,6-dimethoxycarbazol-9-yl)ethylphosphonic acid (MeO-2PACz) as an HTL bilayer, which enhances the crystallinity of the perovskite and improves the energy level alignment between the HTL and the perovskite at the buried interface. Subsequent top surface passivation with 2-phenylethylamine hydroiodide (PEAI) results in the formation of a 2D/3D heterojunction perovskite, leading to a high PCE of 22.91% and excellent long-term operational stability in the resulting device. SCAPS-1D numerical simulations elucidate that the structure of the buried interface significantly impacts PCEs, considering the effects of interface defects, perovskite bulk defects, and interface energy level alignment on device performance. Comprehensive simulations predict an optimal device configuration capable of achieving a PCE of 27.35%. This investigation offers novel insights into the interface properties of cesium-formamidinium (CsFA)-based perovskites and the consequences of energy level shifts, advancing the field of MA-free PSC design and optimization.