Resolving Mixed Intermediate Phases in Methylammonium-Free Sn-Pb Alloyed Perovskites for High-Performance Solar Cells

The complete elimination of methylammonium (MA) cations in Sn-Pb composites can extend their light and thermal stabilities. Unfortunately, MA-free Sn-Pb alloyed perovskite thin films suffer from wrinkled surfaces and poor crystallization, due to the coexistence of mixed intermediate phases. Here, we report an additive strategy for finely regulating the impurities in the intermediate phase of Cs(0.25)FA(0.75)Pb(0.6)Sn(0.4)I(3) and, thereby, obtaining high-performance solar cells. We introduced d-homoserine lactone hydrochloride (D-HLH) form hydrogen bonds and strong Pb-O/Sn-O bonds with perovskite precursors, thereby weakening the incomplete complexation effect between polar aprotic solvents (e.g., DMSO) and organic (FAI) or inorganic (CsI, PbI2, and SnI2) components, and balancing their nucleation processes. This treatment completely transformed mixed intermediate phases into pure preformed perovskite nuclei prior to thermal annealing. Besides, this D-HLH substantially inhibited the oxidation of Sn2+ species. This strategy generated a record efficiency of 21.61%, with a V-oc of 0.88 V for an MA-free Sn-Pb device, and an efficiency of 23.82% for its tandem device. The unencapsulated devices displayed impressive thermal stability at 85 degrees C for 300 h and much improved continuous operation stability at MPP for 120 h.

Automated summary

By employing an additive strategy, the impurities in the intermediate phase of Cs(0.25)FA(0.75)Pb(0.6)Sn(0.4)I(3) were finely regulated, resulting in high-performance solar cells with improved efficiency and stability for MA-free Sn-Pb devices.