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

We demonstrate a facile morphology-controllable sequential deposition of planar CH3NH3PbI3 (MAPbI(3)) film by using a novel volume-expansion-adjustable PbI2 center dot xMAI (x: 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 center dot xMAI with adjustable morphology, which result in about 10-fold faster formation of planar MAPbI(3) 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 center dot 0.15MAI is 17.22% (under one sun illumination), which is consistent with the stabilized maximum power output at an efficiency of 16.9%.