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

We use a popular organic-inorganic hybrid perovskite, methyl-ammonium lead iodide (MAPbI3), 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 MAPbI3 with a smaller inorganic cation, cesium (Cs+), or the larger organic cation, formamidinium (FA), to form the mixed-A cation perovskites, FAxMA1-xPbI3 and CsxMA1-xPbI3, respectively.We demonstrated a significant improvement in the TFT switching speed and ON/OFF ratio with CsxMA1-xPbI3 but failed to achieve any transistor operation with FAxMA1-xPbI3. Incorporation of Cs into MAPbI3 reduced bulk and interfacial trap states and improved film density and morphology, whereas incorporationof FAresulted in increasedsurface roughness and thicker grain boundaries.