Engineering the Hole Extraction Interface Enables Single‐Crystal MAPbI3 Perovskite Solar Cells with Efficiency Exceeding 22% and Superior Indoor Response

Abstract Perovskite single crystals have recently been regarded as emerging candidates for photovoltaic application due to their improved optoelectronic properties and stability compared to their polycrystalline counterparts. However, high interface and bulk trap density in micrometer‐thick thin single crystals strengthen unfavorable nonradiative recombination, leading to large open‐circuit voltage ( V OC ) and energy loss. Herein, hydrophobic poly(3‐hexylthiophene) (P3HT) molecule is incorporated into a hole transport layer to interact with undercoordinated Pb 2+ and promote ion diffusion in a confined space, resulting in higher‐quality thin single crystals with reduced interface and bulk defect density, suppressed nonradiative recombination, accelerated charge transport, and extraction. As a result, a remarkably enhanced V OC of up to 1.13 V and efficiency of 22.1% are achieved, which are both the highest values for MAPbI 3 single‐crystal solar cells. Moreover, the reduced defect density and suppressed carrier recombination lead to superior weak light response of the single‐crystal solar cells after incorporation of P3HT, and an indoor photovoltaic efficiency of 39.2% at 1000 lux irradiation is obtained.