Microelectronics is characterized by a wide variety of functional materials whose properties make them suitable for very specific applications. For example, transistors, data storage devices and most photovoltaic cells are made of silicon. In contrast, compound semiconductors such as gallium nitride are used to generate light in optoelectronic elements such as light-emitting diodes (LEDs). Depending on the class of material, the manufacturing processes very greatly. Hybrid perovskite materials - semiconducting crystals whose organic and inorganic components are arranged in a specific crystal structure - promise to simplify this diversity. "Depending on their composition, they can be used to manufacture all kinds of microelectronic components," says Prof. Dr. Emil List-Kratochvil, head of a joint research group of the Helmholtz Centre Berlin and Humboldt University. One advantage is that perovskite crystals allow a comparatively simple method of processing. They can be produced from a liquid solution, allowing the desired component to be built up layer by layer directly from the substrate.
In recent years, scientists at HZB have already shown that solar cells can be printed from a solution of such semiconductor compounds. Now, for the first time, the joint team of HZB and HU Berlin has succeeded in producing functional light-emitting diodes in this way. For this purpose, the research group used a metal halide perovskite - a material that promises particularly high efficiency in light generation, but is difficult to process.
"Until now, it has not been possible to produce such semiconductor layers from a liquid solution of sufficient quality," says List-Kratochvil. For example, LEDs could only be printed from organic semiconductors, which, however, only provide a modest luminosity. The challenge was to use a kind of attractant to induce the salt-like precursor, which the scientists applied to the substrate by printer, to crystallize quickly and uniformly. They chose a "seed crystal" - a salt that attaches itself to the substrate and serves as a scaffold for the growth of the perovskite structure.