Seed-Crystal-Assisted Space-Confined Growth of FASnI₃ Quasi-Single-Crystal Thick Films and Their Photodetection Characteristics

Sn-based perovskites are ideal eco-friendly candidates as an alternative to Pb-based ones in next-generation optoelectronics. However, a polycrystalline Sn-based perovskite thin film deposited from the spin-coating process suffers from high defect density and poor chemical stability, causing inferior performance of optoelectronic devices. Herein, we report the fabrication of a compact FASnI₃ quasi-single-crystal (QSC) thick film by developing a seed-crystal-assisted space-confined (SSG) strategy. The crystal growth dynamics in the SSG process is identified to be crystal size-dependent Ostwald ripening, and the key parameters are carefully investigated. After optimization, a compact n-type FASnI₃ QSC thick film can be produced with exceptional properties, including thickness of 12 μm, crystal size of 36.63 ± 12.24 μm, defect density of 5.68 × 10¹² cm^-3, and charge mobility of 10.1 cm² V^-1 s^-1. The corresponding photodetector exhibits self-driven detection ability and detectivity of 10¹⁰ Jones at low bias of 0.1 V. This work opens up a new avenue for developing high-performing Sn-based optoelectronic devices.