Self-Sacrificed\nAdditive in Preparing PbI<sub>2</sub> Film Enables the Oriented Growth\nof Perovskite Crystals for Improved\nSolar Cell Performance

Due\nto the limitation of the diffusion kinetics of organic amine\nsalts on the PbI<sub>2</sub> layer in the two-step method, prepared\nperovskite particles are small in size, have many defects, and are\nrandomly oriented, and the cell efficiency and stability are difficult\nto guarantee due to PbI<sub>2</sub> residues. Here, we added a volatile\nadditive, <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethylethylenediamine (TMEDA),\nto the PbI<sub>2</sub> precursor solution and formed preaggregated\natomic clusters with PbI<sub>2</sub> through TMEDA, which reduced\nthe Gibbs free energy of nucleation to obtain a porous PbI<sub>2</sub> layer, and finally obtained a perovskite film with large particles,\nfew defects, ideal crystal plane orientation, and no additive residues.\nThe results show that the photoelectric conversion efficiency of the\noptimized device is increased by 1.68% (from 21.68% to 23.36%), and\nthe unpackaged optimized device still maintains the maximum efficiency\nof 77% after being placed in the air for 1200 h. This study provides\nan effective way to fabricate efficient and stable perovskite solar\ncells by promoting the nucleation-induced crystallization orientation\nby volatile additives.