Volatile eutectics to tailor crystallization for perovskite optoelectronics

Improvements to the radiative efficiency of halide perovskite thin films are necessary to approach fundamental solar cell performance limits. We tailored perovskite crystallization by leveraging the eutectic interaction between zinc bromide and methylammonium chloride additives. The resulting films had high photoluminescence quantum yield and charge carrier decay times and low surface recombination velocity. Nanoprobe x-ray microscopy revealed local melting of the eutectic at grain boundaries during annealing that reduced intragranular structural defect density. Annealing also homogenized the halide distribution and caused zinc segregation to grain boundaries. Solar cells fabricated with the volatile eutectic reached 26.5% power conversion efficiency (PCE, certified 25.9%), and perovskite minimodules (areas more than 15 square centimeters) had 23.9% PCE. Small-area cells with a poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] hole transporter retained 85.8% of their initial 24.1% PCE after 1400 hours of continuous operation at 85°C. Furthermore, this approach enables 26.1% external quantum efficiency as light-emitting diodes.