Study of step annealing method and the effect on optical, structural, morphological and transport properties of CH3NH3PbI3

Thermal annealing is used as a post-deposition processing method for the formation of solid-state organic-inorganic perovskite film of required phase by removing the remnant solvent in as coated film. In the present work, we have studied temperature, time and the application of giving a temperature step for thermal-annealing process. To provide temperature step heating treatment was given to the spin coated film in two consecutive steps; initially heating at lower temperature followed by at 100 degrees C for 30 min. We show that initial lower temperature annealing step improves crystallite size by retarding crystalline growth due to slower solvent evaporation and obtain improved absorption, phase, surface coverage and mobility. However, if this lower temperature step is not sufficient to step up the formation of desired phase, the second step of higher temperature annealing is also not able to form perovskite phase. This study is supported by studies like UV-visible absorption spectroscopy, Raman spectroscopy, X-ray diffraction, scanning electron microscopy, SCLC measurements etc.