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.
In this way, the researchers created printed LEDs with far higher luminosity and significantly better electrical properties than could previously be achieved with additive manufacturing processes. For List-Kratochvil, however, this success is only an intermediate step on the way to future micro- and optoelectronics, which in his opinion will be based exclusively on hybrid perovskite semiconductors. “The advantages offered by a universally applicable class of materials, from which any components can be manufactured using a single simple and cost-effective process, are impressive,” says the scientist. In his Berlin laboratory in Berlin, he therefore intends to gradually manufacture all relevant electronic components in this way.
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