A facile way to prepare nanoporous PbI2 films and their application in fast conversion to CH3NH3PbI3

In this report, we demonstrate a facile way to prepare PbI2 films with interpenetrating nanopores. The nanoporous PbI2 (n-PbI2) films were prepared by the solvent-solvent extraction (SSE) method, in which the DMF solvent was effectively extracted by isopropanol (IPA) within seconds, resulting in well-crystallized n-PbI2 films without annealing. The mechanism involved in the preparation of n-PbI2 films using the SSE method was studied further, and some universal rules for fabricating n-PbI2 films with the SSE method were proposed. The interpenetrating nanoporous morphology enabled fast penetration of the CH3NH3I (MAI) solution, so most of the PbI2 converted into CH3NH3PbI3 within 10 s even with a perovskite overlayer of 300 nm. Moreover, the perovskite layer was pinhole-free and smoother than that based on a conventional PbI2 film. Consequently, perovskite solar cells based on n-PbI2, with the setup as FTO/compact TiO2/bilayer CH3NH3PbI3/P3HT/Ag, delivered an impressive power conversion efficiency of 10.1%, compared with 5.9% for its counterpart based on a conventional compact PbI2 film. This work unveils the PbI2-morphology-related reaction kinetics in the two-step method, and will contribute to understanding the role PbI2 films play in the preparation of perovskites.