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 PEA2FAn-1SnnI3n-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 cm2 V−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. Wu et al. report the sequential crystallization in quasi-2D tin-based perovskites, achieved by preferential formation of low-dimensional templates and delayed 3D growth, yielding vertically oriented and low-defect films for field-effect transistors with high mobility, negligible hysteresis, and improved stability.