Ionic liquid engineering enabled in‐plane orientated 1D perovskite nanorods for efficient mixed‐dimensional perovskite photovoltaics

Abstract Mixed‐dimensional engineering of perovskite material has been demonstrated as a facile and promising strategy to improve both photovoltaic performance and long‐term stability of perovskite solar cells (PSCs). In this study, we report an in‐plane preferred orientation of 1D perovskite induced by an ionic liquid (IL) of 1‐(3‐cyanopropyl)‐3‐methylimidazolium chloride (CPMIMCl) for the first time via sequential deposition approach, leading to a mixed dimensional perovskite thin films. The generated one‐dimensional (1D) CPMIMPbI 3 with in‐plane orientation resides at the grain boundaries of three‐dimensional (3D) perovskite can be appreciably observed from the morphology level, leading to creation of high‐quality films with large grain size with more efficient defect passivation. Moreover, the dispersion of IL in the bulk phase of perovskite material allows for the formation of 1D perovskite for multiple level passivation to inhibit non‐radiative recombination and optimize carrier transport. This IL engineering strategy not only yields a mixed‐dimensional perovskite heterostructure with in‐plane orientation 1D perovskite nano‐rods but also significantly improves the opto‐electronic property with suppressed trap states. As a result, the CPMIMCl‐treated PSCs show an enhanced photovoltaic performance with a champion power conversion efficiency (PCE) up to 24.13%. More importantly, benefiting from the hydrophobicity of formed 1D perovskite and defects suppression, the corresponding PSC demonstrates an excellent long‐term stability and maintain 97.1% of its pristine PCE at 25°C under 50% RH condition over 1000 h. This research provides an innovative perspective for employing the low dimensional engineering to optimize the performance and stability of photovoltaic devices. image