Self-Sacrificed Additive in Preparing PbI2 Film Enables the Oriented Growth of Perovskite Crystals for Improved Solar Cell Performance

Due to the limitation of the diffusion kinetics of organic amine salts on the PbI₂ layer in the two-step method, prepared perovskite particles are small in size, have many defects, and are randomly oriented, and the cell efficiency and stability are difficult to guarantee due to PbI₂ residues. Here, we added a volatile additive, N,N,N',N'-tetramethylethylenediamine (TMEDA), to the PbI₂ precursor solution and formed preaggregated atomic clusters with PbI₂ through TMEDA, which reduced the Gibbs free energy of nucleation to obtain a porous PbI₂ layer, and finally obtained a perovskite film with large particles, few defects, ideal crystal plane orientation, and no additive residues. The results show that the photoelectric conversion efficiency of the optimized device is increased by 1.68% (from 21.68% to 23.36%), and the unpackaged optimized device still maintains the maximum efficiency of 77% after being placed in the air for 1200 h. This study provides an effective way to fabricate efficient and stable perovskite solar cells by promoting the nucleation-induced crystallization orientation by volatile additives.