A family of materials long investigated for their suitability for photovoltaic applications is also showing promise for high-brightness LEDs.
The term "perovskite" refers to a material whose crystal structure is similar to that of the mineral of the same name. The mineral Perovskite, CaTiO3, was discovered in the Ural Mountains in 1839 by Gustav Rose and named by him for the Russian geologist Lev Perovski. Its crystal structure was described in 1926 by Victor Goldschmidt.
Synthetic materials with the so-called "perovskite structure" are often in the form ABX3, where A represents a large metal cation, B a somewhat smaller one, and X either oxygen or a halide.
Researchers from Cambridge and Oxford universities in England, and the Ludwig-Maximilians-Universität in Germany, have experimented with organometal halide perovskites and discovered that, in a simple and scaleable process in which a perovskite solution is prepared and spin-coated onto a substrate, the substance can produce bright LED light whose frequency is simple to pre-determine. No heating and no vacuum required.
They call these novel LEDs "PeLEDs."
The material the researchers investigated, in the form ABX3, had methylammonium in the A position, lead (Pb) for B, and either Br, Cl, or I for X. Here is the abstract of their paper in Nature Nanomaterials.
The researchers were able to produce infrared, red, and green light by varying the composition of the halide (X) component. They write:
In our infrared device, a thin 15 nm layer of CH3NH3PbI3-xClx perovskite emitter is sandwiched between larger-bandgap titanium dioxide (TiO2) and poly(9,9′-dioctylfluorene) (F8) layers, effectively confining electrons and holes in the perovskite layer for radiative recombination. We report an infrared radiance of 13.2 W sr−1 m−2 at a current density of 363 mA cm−2, with highest external and internal quantum efficiencies of 0.76% and 3.4%, respectively.
The team is working on raising the efficiency of the process and says that we could see production PeLEDs within five years.
— Keith Dawson , Editor-in-Chief, All LED Lighting