Gated Photodetector with a Bipolar Response from Single-Crystal Halide Perovskite Using a Polymeric Electrolyte as the Gate Dielectric

In this report, we show that a gated optical detector working in the visible wavelength region can be made on single-crystal halide perovskite methylammonium lead bromide (CH3NH3PbBr3 or MAPB). A polymeric electrolyte (PEO/LiClO4) is used as the gate dielectric, which forms an electric double layer (EDL) at the electrolyte/MAPB interface, leading to high specific gate capacitance and enabling enhanced carrier induction at a low gate bias. The photoresponse of the detector can be enhanced significantly by a large factor (e.g., by a factor of 35) by a bias Vg of 10 V. The core gate operation is due to the field effect, and the detector shows the characteristics of a field effect transistor (FET) with bipolar nature, thereby operating with both polarities of the gate bias. This is enabled by the special feature of halide perovskites, that is, they have appreciable mobility for both types of carriers. It is established that the enhancement of the detector current response occurs due to the synergy of carriers created by illumination as well as the gate when they are present simultaneously, which modifies the near-band-edge trap states close to valence band maxima (VBM) and conduction band minima (CBM) and enhances the carrier mobility. The proposed synergy mechanism is validated by the gate-induced enhancement of the photoluminescence (PL) emission intensity and narrowing of the emission line.