Annealing time effects on the structural, morphological and optical properties in hybrid CH3NH3PbI3 perovskites: Experimental and ab-initio investigations

Abstract We report on the effects of annealing time on the structural, morphological and optical properties of hybrid CH3NH3PbI3 perovskite powders. X-ray diffraction analysis confirms the tetragonal structure. We demonstrate a conversion of the intermediate phase into perovskite phase with increasing annealing time. Higher purity in which the intermediate phase undergoes a complete transition to perovskite was obtained after annealing time of 4 h at a temperature of 110 °C. The crystallite size increases with increasing annealing time. Scanning electron microscope allows to observe micro-sticks, in which their diameters increases with increasing annealing time. The optical properties of hybrid perovskite were studied using UV–visible spectroscopy and ab-initio calculations. The band gap energy decreases, while the refractive index increases with increasing annealing time. These changes can be understood by the decrease of lattice parameters with increasing annealing times, as supported by ab-initio calculations.