Perovskites for a New Class of LED

Photographs of centimeter-scaled thin films of nanocrystalline perovskites under UV illumination. (Source: S. Demchyshyn et al., Sci. Adv. / LMU)

Light-emitting diodes produce light of a defined color within the spectral range from the infrared to the ultra­violet. The exact wave­length of the emission is deter­mined by the chemical composition of the semi­conductor employed, which is the crucial component of these devices. In the case of some semicon­ducting materials, the color can also be tuned by appro­priately modi­fying the size of the crystals of which the light-emitting layer is composed. In crystals with dimen­sions on the order of a few nano­meters, quantum mecha­nical effects begin to make them­selves felt.

LMU researchers in colla­boration with col­leagues at the Univer­sity of Linz, Austria, have now developed a method for the production of semicon­ducting nanocrystals of defined size based on the cheap mineral oxide known as perovs­kite. These crystals are extremely stable, which ensures that the LEDs exhibit high color fide­lity – an important criterion of quality. Moreover, the resulting semi­conductors can be printed on suitable surfaces, and are thus predestined for the manu­facture of LEDs for use in displays.

The crucial element in the new method is a thin wafer, only a few nano­meters thick, which is patterned like a waffle. The depressions serve as tiny reaction vessels, whose shape and volume ulti­mately determine the final size of the nano­crystals. “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“, says LMU researcher Bert Nickel, member of the Nano­systems Ini­tiative Munich (NIM), a Cluster of Excellence.

Moreover, the wafers are produced by means of an economical electro­chemical process, and can be fashioned directly into LEDs. “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,” as Martin Kalten­brunner of the Johannes Kepler Uni­versity in Linz explains. 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. (Source: LMU)

Reference: S. Demchyshyn et al.: Confining metal-halide perovskites in nanoporous thin films, Sci. Adv. 3, e1700738 (2017); DOI: 10.1126/sciadv.1700738

Link: Center for NanoScience (CeNS), Ludwig-Maximilians-University München, Munich, Germany • Linz Institute for Organic Solar Cells (LIOS), Institute of Physical Chemistry, Johannes Kepler University Linz, Linz, Austria

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