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

Abstract

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.