Printed Perovskite LEDs

Graphic representation of the printing process for the perovskite LED. (Source: C. Rothkirch, HU Berlin)

A team of researchers from the Helmholtz-Zentrum Berlin HZB and Humboldt-Univer­sität zu Berlin has succeeded for the first time in producing light-emitting diodes from a hybrid perovskite semi­conductor material using inkjet printing. This opens the door to broad application of these materials in manu­facturing many different kinds of elec­tronic components. The scientists achieved the break­through with the help of a trick: inocula­ting or seeding) the surface with specific crystals.

Micro­electronics utilise various functional materials whose properties make them suitable for specific appli­cations. For example, transistors and data storage devices are made of silicon, and most photo­voltaic cells used for generating electricity from sunlight are also currently made of this semi­conductor material. In contrast, compound semi­conductors such as gallium nitride are used to generate light in opto­electronic elements such as LEDs. The manu­facturing processes also different for the various classes of materials. Hybrid perovskite materials promise simplification – by arranging the organic and inorganic components of semi­conducting crystal in a specific structure. “They can be used to manu­facture all kinds of micro­electronic components by modifying their composition“, says Emil List-Kratochvil, head of a Joint Research Group at HZB and Humboldt-Universität.

What’s more, processing perovskite crystals is compara­tively simple. “They can be produced from a liquid solution, so you can build the desired component one layer at a time directly on the substrate“, the physicist explains. The scientists at HZB have already shown in recent years that solar cells can be printed from a solution of semi­conductor compounds – and are worldwide leaders in this tech­nology today. Now for the first time, the joint team has succeeded in producing functional light-emitting diodes in this manner. The group used a metal halide perovskite for this purpose. This is a material that promises parti­cularly high efficiency in generating light – but on the other hand is difficult to process.

“Until now, it has not been possible to produce these kinds of semi­conductor layers with sufficient quality from a liquid solution“, says List-Kratochvil. For example, LEDs could be printed just from organic semi­conductors, but these provide only modest lumi­nosity. “The challenge was how to cause the salt-like precursor that we printed onto the substrate to crystal­lize quickly and evenly by using some sort of an attractant or catalyst“, explains the scientist. The team chose a seed crystal for this purpose: a salt crystal that attaches itself to the substrate and triggers formation of a gridwork for the subsequent perovskite layers.

In this way, the researchers created printed LEDs that possess far higher lumi­nosity and considerably better electrical properties than could be previously achieved using additive manu­facturing processes. But for List-Kratochvil, this success is only an inter­mediate step on the road to future micro- and opto­electronics that he believes will be based exclu­sively on hybrid perovskite semi­conductors. “The advantages offered by a single universally applicable class of materials and a single cost-effective and simple process for manu­facturing any kind of component are striking“, says the scientist. He is therefore planning to eventually manufacture all important electronic components this way in the labora­tories of HZB and HU Berlin. (Source: HZB)

Reference: F. Hermerschmidt et al.: Finally, inkjet-printed metal halide perovskite LEDs – utilizing seed crystal templating of salty PEDOT:PSS, Mater. Horiz., online 27 May 2020; DOI: 10.1039/D0MH00512F

Link: Hybrid Materials Formation and Scaling (E. Unger), Helmholtz-Zentrum Berlin für Materialen und Energie, Berlin, Germany

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