Managing Excess Lead Iodide with Ordered Distribution and Reduced Photoactivity via Chelating Ligands for Stable Inverted Perovskite Solar Cells.

Excess lead iodide (PbI 2 ) aggregates distributed in perovskite photoreactive absorbers will perturb carrier collection and become a key source of instability in PSCs. Herein, a multisite heterocyclic ligand of 2-mercaptonicotinic acid (2-MNA) is introduced as a chelating agent to manage excess PbI 2 in inverted PSCs. The chelating coordination of 2-MNA to Pb 2+ ions through the carbonyl, sulfhydryl, and pyridinyl groups enables a high-quality perovskite film with reduced PbI 2 aggregates and the formation of an ordered distribution at grain boundaries. Moreover, the coordination of 2-MNA with the [PbX 6 ] 4- octahedron effectively inhibits the photodecomposition of PbI 2 -rich perovskites, thus preventing the generation of metallic lead (Pb 0 ) and iodine (I 2 ) species in response to environmental stimuli. As a result, the inverted PSC based on a 2-MNA modified triple cation perovskite photoactive layer achieves a PCE of 21.27% and a fill factor of 82.07%, accompanied by improved thermal and photostability.