Regulating Surface Metal Abundance via Lattice-Matched Coordination for Versatile and Environmentally-Viable Sn-Pb Alloying Perovskite Solar Cells.

Narrow-bandgap Sn-Pb alloying perovskites showcased great potential in constructing multiple-junction perovskite solar cells (PSCs) with efficiencies approaching or exceeding the Shockley-Queisser limit. However, the uncontrollable surface metal abundance (Sn and Pb ions) hinders their efficiency and versatility in different device structures. Additionally, the undesired Pb distribution mainly at the buried interface accelerates the Pb leakage when devices are damaged. In this work, a novel strategy is presented to modulate crystallization kinetics and surface metal abundance of Sn-Pb perovskites using a cobweb-like quadrangular macrocyclic porphyrin material, which features a molecular size compatible with the perovskite lattice and robustly coordinates with Pb ions, thus immobilizing them and increasing surface Pb abundance by 61%. This modulation reduces toxic Pb leakage rates by 24-fold, with only ∼23 ppb Pb in water after severely damaged PSCs are immersed in water for 150 h.This strategy can also enhance chemical homogeneity, reduce trap density, release tensile strain and optimize carrier dynamics of Sn-Pb perovskites and relevant devices. Encouragingly, the power conversion efficiency (PCEs) of 23.28% for single-junction, full-stack devices and 21.34% for hole transport layer-free Sn-Pb PSCs are achieved.Notably, the related monolithic all-perovskite tandem solar cell also achieves a PCE of 27.03% with outstanding photostability.