Researchers from the University of Strasbourg and CNRS (France), in collaboration with Nanjing University (China), have devised an original device architecture enabling the fabrication of flexible and recyclable organic light-emitting diodes. These results have been published in the Science Advances.
The devices of tomorrow’s electronics must combine multiple functional units all integrated into high-performance, lightweight, wearable, flexible, and biocompatible technologies for applications in optoelectronics, data storage, environmental sensing, health monitoring, and fast communications. Organic materials combine such unique features and are therefore ideal active components for the next generation of optoelectronic devices. In this framework, the fabrication of large-area displays based on organic and polymeric materials have represented a true technological revolution with the next greatest challenges being associated to the development of high-resolution and highly flexible displays for portable screens and banners.
In the past 25 years, considerable efforts have been made to develop high-performance organic light-emitting materials and devices, addressing the technological needs of the fast-growing market of flexible consumer electronics. Organic light-emitting diodes (OLEDs) are colored light sources in which an organic layer emits light at a given wavelength (determining its color) when an electric current flows through it. OLEDs are widely used in everyday digital displays, such as smartphones and computer screens. Nevertheless, the use of thin films of indium tin oxide (ITO) as transparent electrodes in standard OLEDs limits the development of flexible and rollable applications because of the high cost and limited supply of indium as well as the fragility and lack of flexibility of ITO layers.
In this challenging context, the researchers from Strasbourg and Nanjing have conceived an ingenious asymmetric vertical device architecture relying on a “perforated” gold electrode (with millions of holes in a honeycomb-like arrangement) supported by thousands of individual polymer nanopyramids acting as insulating pillars. On its top surface, the nanomesh electrode is coated with an organic layer that emits yellow light when a voltage is applied.
Remarkably, high electrical performance and mechanical robustness are retained when the ITO-free OLED is fabricated on a flexible substrate (e.g., a polyimide foil). Furthermore, the initial emissive layer can be washed away and recuperated by ultrasonic cleaning, allowing the device to be refilled with another conjugated polymer capable of emitting light of a different color (e.g., green).
These results represent a major step forward for the next generation of high-resolution, flexible/rollable, and recyclable displays, while also offering multiple perspectives for high-performance applications in energy, sensing, and lighting.
A robust vertical nanoscaffold for recyclable, paintable, and flexible light-emitting devices
Yifan Yao, Yusheng Chen, Kuidong Wang, Nicholas Turetta, Stefania Vitale, Bin Han, Hanlin Wang, Lei Zhang, Paolo Samorì*
Sci. Adv., 2022, 8, eabn2225