Sterically Suppressed Phase Segregation in 3D Hollow Mixed-Halide Wide Band Gap Perovskites

Band gap tuning in mixed-halide perovskites enables efficientmultijunctionsolar cells and LEDs. However, these wide band gap perovskites, whichcontain a mixture of iodide and bromide ions, are known to phase segregateunder illumination, introducing voltage losses that limit stability.Previous studies have employed inorganic perovskites, halide alloys,and grain/interface passivation to minimize halide segregation, yetphotostability can be further advanced. By focusing on the role ofhalide vacancies in anion migration, one expects to be able to erectlocal barriers to ion migration. To achieve this, we employ a 3D hollowperovskite structure, wherein a molecule that is otherwise too largefor the perovskite lattice is incorporated. The amount of hollowingagent, ethane-1,2-diammonium dihydroiodide (EDA), varies the densityof the hollow sites. Photoluminescence measurements reveal that 1%EDA in the perovskite bulk can stabilize a 40% bromine mixed-halideperovskite at 1 sun illumination intensity. These, along with capacitance-frequencymeasurements, suggest that hollow sites limit the mobility of thehalide vacancies.

Automated summary

Band gap tuning in mixed-halide perovskites enables efficient multijunction solar cells and LEDs. However, wide band gap perovskites phase segregate under illumination, introducing voltage losses that limit stability. This study explores the role of halide vacancies in anion migration to erect local barriers to ion migration, using a 3D hollow perovskite structure with ethane-1,2-diammonium dihydroiodide (EDA) as the hollowing agent. Results show that 1% EDA can stabilize a 40% bromine mixed-halide perovskite at 1 sun illumination intensity, suggesting that hollow sites limit the mobility of the halide vacancies.