Microstructure study of bismuth oxyiodide thin film prepared by SILAR dip coating

Bismuth Oxyiodide (BiOI) has been recognized as a suitable candidate of non-toxic material to replace lead in perovskite solar cells without reducing its performance. BiOI has been synthesized and deposited using modified successive ionic layer adsorption and reaction (SILAR) dip coating method at room temperature on the microscope glass, as a substrate. The microscope glass was dipped consecutively in 0.1M of bismuth(III) nitrate pentahydrate (BiNO 3 ) 2 .5H 2 O diluted in nitric acid (HNO 3 ) and 0.05M of potassium iodide (KI) in 50 ml deionized water. This process has been repeated for 30 times and finally the sample was dripped and dried in air. The sample was annealed at various annealing temperature from 350, 400, 425 and 450oC, for 1 hour. The physical observation, morphological and thickness of BiOI thin films have been characterized using field emission scanning electron microscope (FE-SEM) and surface profiler, respectively. From the physical observation, the as deposited BiOI thin film shows a thick layer with dark orange colour. The colour of the film changed to the orange-yellow after annealed at 350oC for 1 hour. It was observed that the film become more yellowish with increasing annealing temperature. SEM images demonstrated that the BiOI thin films have flakes morphology structure with the grain sizes around 1μm. The flakes agglomerates and formed a flower platelet. The agglomeration increased with higher annealing temperature and finally shattered when the BiOI was annealed at 450oC.