LAUSR

To date, there are no reports of 3D tin perovskite being used as a semiconducting channel in field‐effect transistors (FETs). This is probably due to the large amount of trap states and high p‐doping typical of this material. Here, the first top‐gate bottom‐contact FET using formamidinium tin triiodide perovskite films is reported as a semiconducting channel. These FET devices show a hole mobility of up to 0.21 cm2 V−1 s−1, an ION/OFF ratio of 104, and a relatively small threshold voltage (VTH) of 2.8 V. Besides the device geometry, the key factor explaining this performance is the reduced doping level of the active layer. In fact, by adding a small amount of the 2D material in the 3D tin perovskite, the crystallinity of FASnI3 is enhanced, and the trap density and hole carrier density are reduced by one order of magnitude. Importantly, these transistors show enhanced parameters after 20 months of storage in a N2 atmosphere.