This image shows (A) photoluminescence and (B) electroluminsecence in low-dimensional and 3D perovskite-based devices. Photoluminescence (PL) is the emission of light caused by the absorption of incident photons, whereas electroluminescence (EL) is the emission of light caused by an electric current. Although low-dimensional perovskite exhibits better PL properties than 3D perovskite, the latter has better EL properties, which can be exploited to design very bright and efficient PeLEDs. Image: Applied Physics Reviews.
This image shows (A) photoluminescence and (B) electroluminsecence in low-dimensional and 3D perovskite-based devices. Photoluminescence (PL) is the emission of light caused by the absorption of incident photons, whereas electroluminescence (EL) is the emission of light caused by an electric current. Although low-dimensional perovskite exhibits better PL properties than 3D perovskite, the latter has better EL properties, which can be exploited to design very bright and efficient PeLEDs. Image: Applied Physics Reviews.

Scientists at Tokyo Institute of Technology in Japan have discovered a new strategy for designing incredibly efficient perovskite-based light-emitting diodes (LEDs) with record-breaking brightness by leveraging the quantum confinement effect. The scientists report their strategy in a paper in Applied Physics Reviews.

Several techniques for generating light from electricity have been developed over the years. Devices that can emit light when an electric current is applied are referred to as electroluminescent devices, which have become orders of magnitude more efficient than the traditional incandescent light bulb. LEDs are currently the most well-known and widely used electroluminescent devices. Various different types of LED exist nowadays, and this has been made possible by advances in our understanding of quantum mechanics, solid-state physics and the use of alternative materials.

Electroluminescent devices consist of several layers, with the most important being the emission layer (EML), which emits light in response to an electric current. Metal halide perovskites are considered to be promising EML materials. However, current perovskite-based LEDs (PeLEDs) perform poorly compared with organic LEDs, which are typically used to produce displays for TVs and smartphones.

Several researchers have suggested fabricating PeLEDs using thin sheets of low-dimensional perovskites that offer improved light-emission performance based on the quantum confinement effect of excitons. An exciton is an electron-hole pair that can emit a photon efficiently. Unfortunately, low-dimensional perovskites have an intrinsic drawback: the conducting properties of these materials are very poor, due to low electron and hole mobilities, which leads to a low power efficiency.

Now, however, a team of researchers led by Hideo Hosono at the Tokyo Institute of Technology has discovered that it is possible to design highly efficient PeLEDs using three-dimensional (3D) perovskites. Such 3D perovskites have superior electron and hole mobilities, and hence would address the limitation of low-dimensional perovskites. The team investigated whether the quantum confinement effect that occurs in low-dimensional materials could also be achieved in 3D materials.

In an electroluminescent device, the EML is sandwiched between two layers: the electron transport layer and the hole transport layer. These two layers play a key role in ensuring the device has good conducting properties. The team found that the energy-level characteristics of these layers also play a crucial role in the emission efficiency of the EML.

By tuning the characteristics of the electron and hole transport layers in PeLEDs, the team found they could confine excitons to the emission layer, just like in low-dimensional perovskites. "The whole device structure can be regarded as a scaled-up low-dimensional material in a sense, if the energy levels of the electron/hole transport layers are sufficient for exciton confinement," explains Hosono. The team reported 3D PeLEDs with record-breaking performance in terms of brightness, power efficiency and low operating voltage.

This research also sheds light on how the exciton-related properties of a material can be influenced by the adjacent layers, and provides a strategy that can be readily exploited in the development of optical devices. "We believe this study provides new insight into the realization of practical PeLEDs," concludes Hosono.

This story is adapted from material from Tokyo Institute of Technology, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.