Controllable Heterogenous Seeding‐Induced Crystallization for High‐Efficiency FAPbI3‐Based Perovskite Solar Cells Over 24%

The addition of small seeding particles into a supersaturated solution is one among the most effective approaches to obtain high-quality semiconductor materials via increased crystallization rates. However, limited study is conducted on this approach for the fabrication of perovskite solar cells. Here, a new strategy-"heterogenous seeding-induced crystallization (hetero-SiC)" to assist the growth of FAPbI3 -based perovskite is proposed. In this work, di-tert-butyl(methyl)phosphonium tetrafluoroborate is directly introduced into the precursor, which forms a low-solubility complex with PbI2 . The low-solubility complex can serve as the seed to induce crystallization of the perovskite during the solvent-evaporation process. Various in situ measurement tools are used to visualize the hetero-SiC process, which is shown to be an effective way of manipulating the nucleation and crystal growth of perovskites. The hetero-SiC process greatly improves the film quality, reduces film defects, and suppresses nonradiative recombination. A hetero-SIC proof-of-concept device exhibits outstanding performance with 24.0% power conversion efficiency (PCE), well over the control device with 22.2% PCE. Additionally, hetero-SiC perovskite solar cell (PSC) stability under light illumination is enhanced and the PSC retains 84% of its initial performance after 1400 h of light illumination.