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

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 cm 2 V -1 s -1 to 16 cm 2 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) 2 SnI 4 transistor exhibits hole mobility of up to 0.34 cm 2 V -1 s -1 at 295 K and a higher value of 1.8 cm 2 V -1 s -1 at 100 K. Our work provides an important insight into the grain engineering of 2D perovskites for high-performance FETs.