Fast-Switching Mixed A-Cation Organic-Inorganic Hybrid Perovskite TFTs

We use a popular organic-inorganic hybrid perovskite, methyl-ammonium lead iodide (MAPbI 3 ), for thin-film transistors (TFTs). Given the sensitivity of organic-based perovskites to wet processes, we employed an inverted coplanar TFT structure with a UV-treated, high-k AlOx gate insulator and deposited the perovskite from solution into a photoresist bank as the final process step. We also explored the impact of substitutional doping of the MAPbI 3 with a smaller inorganic cation, cesium (Cs + ), or the larger organic cation, formamidinium (FA), to form the mixed-A cation perovskites, FA x MA 1-x PbI 3 and Cs x MA 1-x PbI 3 , respectively. We demonstrated a significant improvement in the TFT switching speed and ON/OFF ratio with Cs x MA 1-x PbI 3 but failed to achieve any transistor operation with FA x MA 1-x PbI 3 . Incorporation of Cs into MAPbI 3 reduced bulk and interfacial trap states and improved film density and morphology, whereas incorporation of FA resulted in increased surface roughness and thicker grain boundaries.