Record Efficiency for Perovskite-Based LED

Efficient near-infrared (NIR) light-emitting diodes of perovskite have been produced in a labora­tory at Linköping Uni­versity. The external quantum effi­ciency is 21.6%, which is a record. The work is led by LiU scientist Feng Gao, in close colla­boration with colleagues in China, Italy, Singapore and Switzer­land.

NIR-LED with external quantum efficiency of record-high 21.6 percent. (Source: T. Balkhed)

Perovskites are a group of materials defined by their crystal structure, and have been the focus of intense research interest during the past 10 years, initially for solar cells and recently also for light emitting diodes. They have good light-emitting proper­ties and are easy to manu­facture. The external quantum effi­ciency of light-emitting diodes based on perovskites has until now been limited by defects that arise in the material during manu­facture. The defects act as traps for the charge carriers and thus cause energy losses.

One way of dealing with defects is to add passi­vation molecules, which bind to the atoms that cause defects. The researchers had previously discovered a molecule with amino groups at its ends that gave a certain improvement in properties. However, when they selected a molecule that also contained oxygen atoms, the effect increased drama­tically. “We now understand that it is the hydrogen bonds between passi­vation molecules and perovskite materials that cause problems. This allowed us to search for a molecule that was perfect for passi­vation”, says Feng Gao, senior lecturer in the Division of Biomo­lecular and Organic Elec­tronics at Linköping Uni­versity.

The molecule they found has two amino groups at its ends, with oxygen atoms at suitable distances between them. Oxygen atoms reduce the hydrogen bonding ability of amino groups, and hence increase the proba­bility that they interact with defects. The number of traps for charge carriers in the perovskite is signi­ficantly reduced, allowing the charge carriers to recombine and emit light efficiently.

“This particular perovskite material gives highly efficient light-emitting diodes in the near-infrared region. Near-infrared light-emitting diodes are parti­cularly useful for medical and telecommu­nication appli­cations. We believe that our new findings can also be applied to perovskite light-emitting diodes with other colours”, says Feng Gao. The external quantum efficiency is a record-high 21.6%.

“We have developed the best light-emitting diodes in perovskite material yet. They can also compete with light-emitting diodes based on, for example, organic materials”, says Wiedong Xu, postdoc in the Division of Biomo­lecular and Organic Electronics, LiU. (Source: Linköping U.)

Reference: W. Xu et al.: Rational molecular passivation for high-performance perovskite light-emitting diodes, Nat. Phot., online 25 March 2019; DOI: 10.1038/s41566-019-0390-x

Link: Biomolecular and Organic Electronics, Dept. of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, Sweden

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