A Soldering Flux Tackles Complex Defects Chemistry in Sn-Pb Perovskite Solar Cells.

Developing tin-lead (Sn-Pb) narrow-bandgap perovskites is crucial for the deployment of all-perovskite tandem solar cells, which can help to exceed the limits of single-junction photovoltaics. However, the Sn-Pb perovskite suffers from a large number of bulk traps and interfacial nonradiative recombination centers, with unsatisfactory open-circuit voltage and the consequent device efficiency. Herein, for the first time, it is shown that abietic acid (AA), a commonly used flux for metal soldering, effectively tackles complex defects chemistry in Sn-Pb perovskites. The conjugated double bond within AA molecule plays a key role for self-elimination of Sn4+-Pb0 defects pair, via a redox process. In addition, C═O group is able to coordinate with Sn2+, leading to the improved antioxidative stability of Sn-Pb perovskites. Consequently, a ten-times longer carrier lifetime is observed, and the defects-associated dual-peak emission feature at low temperature is significantly inhibited. The resultant device achieves a power conversion efficiency improvement from 22.28% (Ref) to 23.42% with respectable stability under operational and illumination situations.