Efficient and Highly Stable Lateral Perovskite Single‐Crystal Solar Cells through Crystal Engineering and Weak Ion Migration

Abstract The lateral device structure for perovskite solar cells (PSCs) has garnered significant attention, primarily due to its elimination of the need for expensive transparent electrodes. However, the performance of lateral devices, which are more sensitive to crystal quality and charge carrier transport bottlenecks, has lagged far behind the predominant vertical PSCs. Herein, by modulating the crystal nucleation and growth processes of thin FA 0.75 MA 0.25 PbI 3 (FA = formamidinium; and MA = methylammonium) single crystals, crystal quality and carrier transport are improved, resulting in a power conversion efficiency (PCE) of 12.64%, a record for lateral PSCs. Investigation of the device's stability reveals that iodide ion migration is suppressed due to a reduction in the iodide vacancy concentration combined with weak interface iodide ion migration. It is shown that the latter effect is a result of the perpendicular direction of the ion migration and the electric field in the lateral PSCs. Consequently, these lateral single‐crystal PSCs display remarkable operational stability, retaining 100% of their initial PCE after 1200 h of steady‐state output at the maximum power point voltage (Vmpp) under 1 sun illumination. This work highlights the advantages of lateral single‐crystal devices and their potential to address key ion migration issues of PSCs.