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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.
Hoang et al. (Mon,) studied this question.