Low-dimensional templates and delayed crystallization for high-quality tin-based perovskite films and high-performance transistors

Quasi-2D tin-based perovskites are promising p-type semiconductors due to their thermodynamic stability and suppressed ion migration tendencies. However, the competitive growth of low- and high-dimensional phases leads to pronounced structural disorder, increased defect density, and poor crystallographic orientation, thereby restricting charge transport. Here, phenethylammonium thiocyanate (PEASCN) is incorporated into the precursor to promote the preferential formation of PEA₂FA_n-1Sn_nI_3n-1SCN₂ (n = 2) templates. Substituting formamidinium iodide (FAI) with formamidinium formate (FAHCOO) and ammonium iodide (NH₄I) suppresses the uncontrollable growth of 3D FASnI₃ at room temperature, enabling precise crystallization control. These low-dimensional templates guide the growth of high-dimensional phases upon annealing, yielding vertically oriented films with reduced defects. The fabricated field-effect transistors exhibit mobility up to 43 cm²V^-1 s^-1 and an on/off ratio exceeding 10⁸, alongside nearly negligible hysteresis and enhanced stability. These results demonstrate a viable approach for regulating crystallization kinetics and realizing high-performance, stable tin-based perovskite devices.