The effect of grain improvement on carrier lifetime in perovskite solar devices

The grain size of the organometallic halide perovskite, methylammonium lead iodide (MAPbI
₃
) was modified through a solvent annealing technique. Dimethyl sulfoxide (DMSO) solvent was found to coalesce perovskite grains leading to improved carrier lifetimes and solar device performance. Samples with three ratios (1.0, 1.1, and 1.2) of PbI
₂
/(CH
₃
NH
₃
I) were used for this study. SEM images of the film surface showed improvement in the grain size with the amount of the solvent used during the annealing. In addition, the number of pinholes was also reduced by solvent annealing. The increased grains directly lead to increased carrier lifetimes and the device efficiency. The optimal device efficiency was observed for the ratio 1.1 of PbI
₂
/(CH
₃
NH
₃
I) and the solvent volume of 5 μL. As the solvent volume increased further, segregated regions of lead rich grains formed among the large grains, which in turn reduced the device efficiency.