Oxidation-Safe p-Doping of Tin-Lead Perovskites Enabled by an Anion-Anchoring Bifunctional Copolymer

초록

Tin-lead perovskites (TLPs) offer near-optimal bandgaps but suffer from spontaneous Sn2+ oxidation and imbalanced charge transport. Conventional p-dopants improve hole extraction yet exacerbate Sn2+ oxidation, creating a fundamental design conflict. Here, we resolve this conflict with a bifunctional copolymer additive, poly(pyrrolidinium-Jeffamine) hexafluorophosphate (PPJ-PF6), in which the polypyrrolidinium backbone electrostatically anchors PF6 - at defect-rich grain boundaries for controlled, non-destructive p-doping, while the Jeffamine polyether segment coordinates and protects Sn2+ against oxidation. Density functional theory calculations confirm favorable polymer-perovskite binding and show that PF6 --induced Fermi-level downshift operates only when the anion is retained within the polymer scaffold. This cooperative mechanism suppresses trap-assisted recombination, improves energy-level alignment, and enhances hole mobility, delivering a champion PCE of 22.8% (from a 21.4% baseline), with unencapsulated devices retaining similar to 80% of initial efficiency after 500 h. These results establish a generalizable design principle: bifunctional polymer scaffolds enabling p-doping while protecting the oxidation-sensitive Sn sublattice.

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