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

Here, a simple strategy using l-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 MAPbI(3) 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.