Tuning phase stability and interfacial dipole for efficient methylammonium-free Sn-Pb perovskite solar cells

The oxidizability and fast crystallization of Sn(II) components commonly cause Sn/Pb phase separation and uncoordinated ion defects on Sn-Pb perovskite film surface. Here, 4-hydroxyphenethylamine hydrochloride (OHPEACl) is introduced to post-treat the Cs0.25FA0.75Pb0.5Sn0.5I3 perovskite film. The ammonium (-NH3+) and reductive phenol hydroxyl (-OH) in OHPEACl are verified to form ionic and hydrogen bonds with organic (FAI) or inorganic components (CsI, SnI2, and PbI2), thereby inhibiting Sn2+ oxidation, anchoring multiple defects sites (unbonded Pb2+, Sn2+, and I-), and promoting uniform distribution of Sn-Pb phases on the film surface. Furthermore, the 4-hydroxyphenethyl ammonium (OHPEA+) with high dipole moment of 9.93 Debye is proved to form reduced and uniform potential landscape of interface dipole, hence aligning energy levels and suppressing non-radiative recombination. Consequently, this strategy raised the efficiency of device from 17.94% to 20.20%, and realized a Voc of 0.84 V for methylammonium (MA) free Sn-Pb device. The unencapsulated devices displayed improved thermal stability at 85 ℃ for 500 h and enhanced continuous operation stability at MPP for 150 h. This approach of introducing multifunctional groups while constructing the interfacial dipole provides a new perspective for improving the quality of Sn-Pb perovskite films.