Grain engineering for improved charge carrier transport in two-dimensional lead-free perovskite field-effect...

Controlling crystal growth and reducing the number of grain boundaries are crucial to maximize the charge carrier transport in organic-inorganic perovskite field-effect transistors (FETs). Herein, the crystallization and growth kinetics of a Sn(II)-based 2D perovskite, using 2-thiopheneethylammonium (TEA) as the organic cation spacer, were effectively regulated by the hot-casting method. With increasing crystalline grain size, the local charge carrier mobility is found to increase moderately from 13 cm² V^-1 s^-1 to 16 cm² V^-1 s^-1, as inferred from terahertz (THz) spectroscopy. In contrast, the FET operation parameters, including mobility, threshold voltage, hysteresis, and subthreshold swing, improve substantially with larger grain size. The optimized 2D (TEA)₂SnI₄ transistor exhibits hole mobility of up to 0.34 cm² V^-1 s^-1 at 295 K and a higher value of 1.8 cm² V^-1 s^-1 at 100 K. Our work provides an important insight into the grain engineering of 2D perovskites for high-performance FETs.