LAUSR

Daily temperature variations induce phase transitions and lattice strains in halide perovskites, challenging their stability in solar cells. We stabilized the perovskite black phase and improved solar cell performance using the ordered dipolar structure of β-poly(1,1-difluoroethylene) to control perovskite film crystallization and energy alignment. We demonstrated p-i-n perovskite solar cells with a record power conversion efficiency of 24.6% over 18 square millimeters and 23.1% over 1 square centimeter, which retained 96 and 88% of the efficiency after 1000 hours of 1-sun maximum power point tracking at 25° and 75°C, respectively. Devices under rapid thermal cycling between −60° and +80°C showed no sign of fatigue, demonstrating the impact of the ordered dipolar structure on the operational stability of perovskite solar cells. Description Running hot and cold Like other solar cells, commercial perovskite solar cells (PSCs) would not only need to maintain operation at the high temperatures generated in direct sunlight but also endure the lattice strain created by temperature changes throughout the year. Li et al. fabricated high-quality perovskite crystalline films by adding a fluorinated polymer, the dipoles of which lowered formation energy of the perovskite black phase, decreased defect density, and also tuned the surface work function for charge extraction. Power conversion efficiencies of 23% were achieved for 1-square-centimeter devices that retained over 90% of their efficiency after testing conditions for 3000 hours and after repeated cycling between −60° and 80°C. —PDS Dipoles in a fluorinated polymer lower the formation energy of a photoactive perovskite phase and reduce its defect density.