Triple‐Cation Mixed‐Halide Perovskite Single‐Crystal Thin‐Film for High‐Performance Photodetector via Adjusting Lattice Strain and Mitigating Surface Defects

Abstract Triple‐cation mixed‐halide (TCMH), i.e., (FAPbI 3 ) 1‐x‐y (MAPbBr 3 ) y (CsPbI 3 ) x , perovskite single‐crystal thin‐films (SCTFs) have emerged as candidates for high‐performance photodetectors. However, high lattice strain, surface defects, and the non‐ideal yellow phase such as δ‐FAPbI 3 and δ‐CsPbI 3 , are impeding the realization of high‐quality TCMH SCTFs. Therefore, the synthesis of pure‐phase, high‐quality TCMH SCTFs with low lattice strain and defect density is imperative for enhancing light absorption and carrier mobility, thereby optimizing photoresponsivity. Herein, an innovative approach is proposed for synthesize TCMH SCTFs using an optimized space‐limited anti‐solvent assisted crystallization technique which employs 2‐methoxyethanol as the solvent and diethyl ether as anti‐solvent, devoid of thermal enhancement. A novel reducing additive, formic acid, is incorporated to mitigate phase separation, and the composition ratio is meticulously adjusted to regulate lattice strain. The results show that a pure‐phased optimal composition ratio (FA 0.82 MA 0.11 Cs 0.07 ) SCTF with a low surface defect density (2.29 × 10 9 cm −2 ), low lattice strain (0.81%) and high hole mobility (77.58 cm −2 V −1 s −1 ) is successfully prepared. Moreover, the non‐integrated planar FA 0.82 MA 0.11 Cs 0.07 SCTF photodetector also achieved a record photo‐responsivity (229.5 A W −1 ), and external quantum efficiency (5.4 × 10 4 %), indicating its great potential in light‐detecting. This research paves the way for the development of high‐performance photodetectors via adjusting lattice strain and mitigating surface defects in TCMH SCTFs.