  Investigation of the inherent field-driven charge transport behaviour of 3D
lead halide perovskites has largely remained a challenging task, owing
primarily to undesirable ionic migration effects near room temperature. In
addition, the presence of methylammonium in many high performing 3D perovskite
compositions introduces additional instabilities, which limit reliable room
temperature optoelectronic device operation. Here, we address both these
challenges and demonstrate that field-effect transistors (FETs) based on
methylammonium-free, mixed-metal (Pb/Sn) perovskite compositions, that are
widely studied for solar cell and light-emitting diode applications, do not
suffer from ion migration effects as their pure Pb counterparts and reliably
exhibit hysteresis free p-type transport with high mobility reaching 5.4
$cm^2/Vs$, ON/OFF ratio approaching $10^6$, and normalized channel conductance
of 3 S/m. The reduced ion migration is also manifested in an activated
temperature dependence of the field-effect mobility with low activation energy,
which reflects a significant density of shallow electronic defects. We
visualize the suppressed in-plane ionic migration in Sn-containing perovskites
compared to their pure-Pb counterparts using photoluminescence microscopy under
bias and demonstrate promising voltage and current-stress device operational
stabilities. Our work establishes FETs as an excellent platform for providing
fundamental insights into the doping, defect and charge transport physics of
mixed-metal halide perovskite semiconductors to advance their applications in
optoelectronic devices.
