The modulation of opto-electronic properties of CH3NH3PbBr3 crystal

The self-doping CH3NH3PbBr3 crystals were fabricated by modulating the molar ratio of PbBr2 to CH3NH3Br from 0.2 to 1.5 to afford p- and n-type materials. The effect of modulating the inorganic to organic content on crystal framework, optical properties, energy level, conductivity, carrier mobility and concentration of CH3NH3PbBr3 crystals were studied by X-ray diffraction (XRD), photoluminescence (PL), photoelectron yield spectroscopy (PYS), Hall-effect measurement and X-ray photoelectric spectroscopy (XPS). It is found that different precursor ratio results in different surface and bulk element composition of the CH3NH3PbBr3 crystals, which influences the intrinsic defects hence the conductivity of perovskite crystals. Low precursor ratios (Pb-poor/Br-rich growth conditions) gave p-doped crystals and vice versa, which is governed by the dominant intrinsic defects of crystals. In addition, the O in the surface composition was much higher than that inside of the crystals, indicating that the crystal surfaces were doped with O to form extrinsic defects.