Global Control of CH₃NH₃PbI₃ Formation with Multifunctional Ionic Liquid for Perovskite Hybrid Photovoltaics

Here, a simple strategy using 1-butyl-3-methylimidazolium iodide (BMII) as a multifunctional additive was employed to globally modify the two-step deposition process of the perovskite film. Morphological, structural, and spectral analyses showed that the BMII additive could coordinate with PbI₂ and thereby retarded the reaction of PbI₂ and CH₃NH₃I through the ionic exchange process. Moreover, the residual BMII provided a liquid domain to promote the coarsening of the perovskite crystal during the thermal annealing process. Thus, the obtained MAPbI₃ film preferred low PbI₂ residue, high-quality crystallization, and large-grained microstructure. Using films prepared with BMII additives, the maximum power conversion efficiency of the solar cells was improved from 12.6% of the reference cell to 15.6%. The present study gives a reproductive and facile strategy toward high quality of perovskite thin films and efficient solar cells