Perovskites are famous for harvesting light in emerging solar cells, but the inexpensive and easy-to-make semiconductors could also provide a simple path to light-emitting devices.
Commercial white light-emitting diodes are made either by combining different colored LEDs or using LEDs that excite phosphor coatings to produce a white glow. Researchers have previously developed a few two-dimensional perovskite crystals that can emit white light without help, but scientists have yet to use them to build a working LED.
Mercouri G. Kanatzidis, Lingling Mao, and coworkers at Northwestern University have outlined perovskite crystal design considerations that could help change that.
The team developed three new lead-bromide materials using different cationic amine “spacers.” In each, lead-bromide octahedra join to form two-dimensional surfaces. These surfaces stack into layers with the organic molecules sandwiched between.
Two of the team’s perovskite crystals are flat, but the one that uses the smallest cation—2-(dimethylamino)ethylamine or DMEN—takes on a buckled, egg-carton structure. This perovskite also emits light over a broad spectrum of wavelengths, resulting in a white light source with a glow akin to that of a fluorescent bulb, the team reports (J. Amer. Chem. Soc. 2017, DOI: 10.1021/jacs.7b01312).
Edward H. (Ted) Sargent, a photovoltaic materials researcher at the University of Toronto, comments that the work is promising for perovskite LEDs. It provides a “powerful new degree of freedom: engineering perovskites via the length and shape of organic ligand,” he adds.
“This is an inorganic synthetic chemist’s dream,” Kanatzidis says of the versatility of these 2-D perovskites. “The system allows you to make changes and gives you new results every time.”