Enhancement in structural and optical properties of Cd doped hybrid organic-inorganic halide perovskite CH3NH3Pb1-xCdxI3 photo-absorber

We report the solution-based synthesis and material characterization of the Cd substituted hybrid organic-inorganic lead halide perovskite CH3NH3Pb1-xCdxI3 (x = 0.0, 0.03, 0.05, 0.08). Structure and morphology of the samples were investigated using XRD, FESEM and HRTEM techniques. XRD results confirmed a tetragonal perovskite structure (I4/mcm) through the doping range. Optical absorption, band gap and bonding character were studied by UV–visible, FTIR and photoluminescence spectroscopy. Oxidation states, binding energy and chemical composition were determined by XPS and EDAX. A low value of Urbach energy (~14 meV) indicated high sample quality with low defects and trap states. The undoped samples had a direct energy gap of 1.56 eV, which reduced to 1.50 eV upon Cd doping. Most significantly, the absorption coefficient of CH3NH3Pb1-xCdxI3 remained high (~103) above 750 nm in the spectrally important infrared range as compared to CH3NH3PbI3, which approached zero. The enhanced structural and optical properties upon Cd doping make these materials promising photo absorber candidates compared to undoped CH3NH3PbI3.