Defect Passivation by a Multifunctional Phosphate Additive toward Improvements of Efficiency and Stability of Perovskite Solar Cells

The quality of perovskite films plays a crucial role in the performance of the corresponding devices. However, the commonly employed perovskite polycrystalline films often contain a high density of defects created during film production and cell operation, including unsaturated coordinated Pb²⁺ and Pb⁰, which can act as nonradiative recombination centers, thus reducing open-circuit voltage. Effectively eliminating both kinds of defects is an important subject of research to improve the power conversion efficiency (PCE). Here, we employ hydrogen octylphosphonate potassium (KHOP) as a multifunctional additive to passivate defects. The molecule is introduced into perovskite precursor solution to regulate the perovskite film growth process by coordinating with Pb, which can not only passivate the Pb²⁺ defect but also effectively inhibit the production of Pb⁰; at the same time, the presence of K⁺ reduces device hysteresis by inhibiting I^- migration and finally realizes double passivation of Pb²⁺ and I^--based defects. Moreover, the moderate hydrophobic alkyl chain in the molecule improves the moisture stability. Ultimately, the optimal efficiency can reach 22.21%.