π-Conjugated Lewis Base for Efficient Tin Halide Perovskite Solar Cells with Retarded Sn2+ Oxidation

Lead-free tin halide perovskite solar cells (TPSCs) have driven much research attention for their environmental friendliness. However, the low efficiency and large open-circuit voltage (Voc) deficit limit their further development. Here, we introduced a π-conjugated Lewis base, 1H-pyrrolo2,3-bpyridin-6-ylaamine (1H6An), a N donor for the unique electron-donating role of pyridine and pyrrole N with unpaired lone pair electrons to interact with the tin halide perovskites and thus retard the oxidation of Sn2+ during the aging process of precursors. Meanwhile, the interaction stabilized the perovskite lattice and decreased the microstrain of deposited films. The carrier kinetics further revealed a notably enhanced carrier extraction and transport as well as decreased nonradiative recombination with 1H6An. Consequently, this approach delivered an efficiency of 13.28% with a remarkable Voc enhancement from 853 to 907 mV. Meanwhile, the 1H6An device exhibited an extended lifespan of over 2500 h with around 90% retention of its initial value in a N2 atmosphere.