Relevance of precursor molarity in the prepared bismuth oxyiodide films by successive ionic layer adsorption and reaction for solar cell application

Bismuth oxyiodide (BiOI) solar cells have been fabricated using a modified successive ionic layer adsorption and reaction (SILAR) method. To adjust the parameter of reaction, we involved the precursor molarity variation from 2 to 10 mM in our BiOI films preparation. The successful formation of BiOI has been indicated by the existence of tetragonal phase BiOI and BiI internal stretching mode in XRD patterns and Raman spectra, respectively. By a gradual increase in precursor molarity, the wide absorption and redshift of BiOI films are observed in the UV-visible spectra. In addition, the large growth of flaky BiOI is displayed in field emission scanning electron microscope (FESEM) image. These characters have an impact on the photovoltaic properties of BiOI films although a monotonous enhancement of solar cell efficiency cannot be reached by the rising concentration of precursors. In this work, we found that the maximum solar cell performance was achieved after an initial concentration increased. Then, it showed a decrease in its performance by increasing precursor molarity. The IV analysis data confirm that BiOI films from 7 mM of precursor have the best Jsc and efficiency which up to ∼2.2 mA/cm2 and 0.318%, respectively. Also, this concentration can result in the maximum external quantum efficiency (EQE). Keywords: BiOI, Precursor concentration, Solar cell, p-type semiconductor, Bismuth material