Low Threshold Voltage Lead–Tin Perovskite Transistors with Enhanced Ambient Stability

Thin-film transistors (TFTs) based on lead-tin perovskites have garnered significant attention for electronic applications due to their high mobilities. However, the facile oxidation of Sn²⁺ to Sn⁴⁺ results in unintended doping, compromising channel modulation and reducing on-off ratios. In this work, we investigate the effect of A- and B-site cation engineering on TFT performance and stability. We demonstrate an ambient-stable device (RH > 70%, 25 °C) with a threshold voltage (<i>V</i>_th) of 4.7 V and an on-off ratio of ∼10⁶, maintaining stability for over an hour without encapsulation. This enhanced performance is attributed to substituting cesium with the larger methylammonium cation, which suppresses Sn oxidation and doping, as supported by XPS and Hall measurements. Such devices with low <i>V</i>_th and high on-off ratios are promising for low-power electronic circuits with reliable and well-defined switching characteristics, highlighting the potential of A-site tuning in perovskite TFTs.