Controllable Sequential Deposition of Planar CH₃NH₃PbI₃ Perovskite Films via Adjustable Volume Expansion

We demonstrate a facile morphology-controllable sequential deposition of planar CH₃NH₃PbI₃ (MAPbI₃) film by using a novel volume-expansion-adjustable PbI₂·<i>x</i>MAI (<i>x</i>: 0.1–0.3) precursor film to replace pure PbI₂. The use of additive MAI during the first step of deposition leads to the reduced crystallinity of PbI₂ and the pre-expansion of PbI₂ into PbI₂·<i>x</i>MAI with adjustable morphology, which result in about 10-fold faster formation of planar MAPbI₃ film (without PbI₂ residue) and thus minimize the negative impact of the solvent isopropanol on perovskites during the MAI intercalation/conversion step. The best efficiency obtained for a planar perovskite solar cell based on PbI₂·0.15MAI is 17.22% (under one sun illumination), which is consistent with the stabilized maximum power output at an efficiency of 16.9%