Nonchemical n- and p-Type Charge Transfer Doping of FAPbI₃ Perovskite

Controlling the Fermi level of semiconductors underlies most electronic and photovoltaic technologies. However, it remains limited to continuously tune the doping levels of the intensively studied lead halide perovskite by introducing any impurities or functional molecules. Here, we report a nonchemical charge transfer doping approach for continuous tuning of the work function (WF) of perovskite. A modification of surface WF from 4.18 to 5.05 eV is achieved by applying a bias voltage and varying its polarity on the formamidinium lead triiodide (FAPbI3) perovskite films via the top Au electrode acting as a medium. Here, n- and p-type charge transfer doping are realized by the negative and positive applied voltages, respectively. The negative applied voltage enhances both carrier mobility and density, leading to an improved conductivity of FAPbI3. The n-type FAPbI3 formed by the applied voltage of −2 V is applied to a dynamic perovskite/spiro-MeOTAD triboelectric device, which results in 1.5 and 3 times increases in DC voltage and current, respectively, as compared to the pristine perovskite without charge transfer doping. This tunable WF by the nonchemical charge transfer doping gives insights into innovational exploitation of the halide perovskite and also provides a new strategy for optoelectronics.