Record efficiency for perovskite LEDs
Swedish-led team shows how improved passivation approach reduces energy losses
Researchers at Linköping University in Sweden have created efficient near-infrared (NIR) LEDs from perovskite with a record external quantum efficiency of 21.6 percent. The results were published in Nature Photonics.
The work was led by Linköping University's Feng Gao in collaboration with colleagues in China, Italy, Singapore and Switzerland
The external quantum efficiency (the ratio of charge carriers emitted as light over all of those fed into the materials) of perovskite LEDs 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 use passiviation 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 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 LEDs in the near-infrared region. Near-infrared LEDs are particularly useful for medical and telecommunication applications. We believe that our new findings can also be applied to perovskite LEDs with other colours", says Feng Gao.
"We have developed the best LEDs in perovskite material yet. They can also compete with LEDs based on, for example, organic materials", says Wiedong Xu, postdoc in the Division of Biomolecular and Organic Electronics, LiU.
'Rational molecular passivation for high-performance perovskite LEDs' by Weidong Xu et al; Nature Photonics 2019