Ludwig Maximilian University (LMU) researchers worked with colleagues at the University of Linz (Austria) to develop a method for the producing semi-conducting nanocrystals of defined size based on perovskite material. These crystals are extremely stable (unlike some other perovskite materials). This stability ensures that LEDs made from the material exhibit high color fidelity. Furthermore, the resulting semiconductors can be printed on suitable surfaces, making them ideal for displays.
An economical electrochemical process produces the wafers, which can be made directly into LEDs. The new method employs a thin, waffle-patterned wafer, only a few nanometers thick. The cavities of the pattern serve as tiny reaction containers. The shape and volume of these depressions ultimately determine the final size of the nanocrystals.
Silicon and Alumina Thin Films Used as Templates for Nanocrystal Growth
The researchers used nanoporous silicon and alumina thin films as templates for growing perovskite nanocrystallites directly within device-appropriate architectures without using colloidal stabilization. They found significantly blue-shifted photoluminescence emission by reducing the pore size. For example, normally green-emitting materials become cyan and blue and infrared-emitting materials become visibly red. The perovskite nanocrystals can apparently be made with several different materials enabling different color emission.
“Optimal measurements of the size of the crystals were obtained using a fine beam of high-energy X-radiation at the Deutsche Elektronen-Synchrotron (DESY) in Hamburg,” said LMU researcher Dr. Bert Nickel, a member of the Nanosystems Initiative Munich (NIM), a Cluster of Excellence.
“Our nanostructure oxide layers also prevent contact between the semiconductor crystals and deleterious environmental factors such as free oxygen and water, which would otherwise limit the working lifetime of the LEDs,” Dr. Martin Kaltenbrunner of the Johannes Kepler University in Linz explained. “In the next step, we want to enhance the efficiency of these diodes further, and explore their potential for use in other applications, such as flexible displays.”
Stepan Demchyshyn et al. Confining metal-halide perovskites in nanoporous thin films, Science Advances (2017). DOI: 10.1126/sciadv.1700738