Green Solvent Engineering and Additive Modulation in Stabilized Black FAPbI3 Perovskite Single Crystals for High-Performance Photodetectors

• • Green solvent GVL replaces toxic GBL, achieving ambient-stable α-FAPbI3 single crystals with markedly improved phase stability, addressing environmental and scalability bottlenecks in perovskite manufacturing. • • Additive modulation with oxalic acid (OA) suppresses δ-phase formation via H+ and reductive groups, yielding FA0.9MA0.1PbI3 single crystal thin films with a low defect density of 8.3 × 10^11 cm−3, critical for high-performance optoelectronics. • • Photodetectors fabricated from these crystals exhibit a responsivity of 14.5 mA/W, detectivity of 3.75 × 10^10 Jones, and response speed of 149/65 μs under zero bias and 780 nm illumination, demonstrating competitive performance for low-power sensing. • • Unencapsulated devices retain 83% of initial performance after 30 days in ambient conditions, indicating exceptional operational stability for practical deployment without costly encapsulation.