Towards efficient self-powered screens
Organic semiconductors –the core technology used in OLED screens –are thin, flexible, and extremely versatile. Researchers would also like to harness the same materials for organic photovoltaics (OPVs). But the ultimate goal would be to combine the two functions into a single multifunctional component.
However, this vision of combining light emission and energy harvesting has been hindered by a seemingly fundamental efficiency trade-off. Devices that combine both functions must leverage delicate processes involving excitons, which are bound states involving an electron and a positively charged hole (an electron vacancy).
Now Japanese researchers have overcome a major technical challenge to creating organic multifunctional devices that both light up and power themselves.
The team led by Hirohiko Fukagawa from the Center for Frontier Science, Chiba University, Japan, has developed a novel design strategy. In their latest paper, published online in Volume 17 of Nature Communications on December 07, 2025, they report an approach centered on precisely controlling the energy state of the excitons using multiple-resonance thermally activated delayed fluorescence (MR-TADF) materials. The team included the first author, Taku Oono, and Takahisa Shimizu from NHK Science & Technology Research Laboratories, Japan, as well as Takuji Hatakeyama from Kyoto University, Japan.
For light-emitting functionality, one needs excitons to tightly recombine to create light. Conversely, for power-generating functionality, one needs excitons to quickly dissociate into free electric charges that can be collected elsewhere. This results in a trade-off that has hindered the development of a single component, comprising both functionalities. Designing a single component that can efficiently perform both at the same time has been considered nearly impossible, with previous attempts achieving very limited success in terms of performance.
The researchers realised that the key to unlocking dual functionality lies in managing the exciton binding energy (Eb), which is the energy holding the electron and hole together. By carefully selecting specific MR-TADF materials as the light-emitting and absorbing components, the team was able to create electron donor/acceptor interfaces that yielded remarkably low Eb values. “Devices with smaller Eb exhibit minimal voltage loss, enabling near-ideal power-generation behaviour,” explains Fukagawa.
This precise control over Eb also enabled the researchers to adjust the material’s emission colour. Relatively large Eb values led to yellow emission from charge-transfer excitons, which are electron–hole pairs that reside on neighboring molecules at the donor/acceptor interface. Meanwhile, smaller Eb values produced blue emission from the MR-TADF donor. Thus, by precisely tuning the material composition at the interface, the researchers realised full-colour operation across the visible spectrum.
By overcoming the efficiency trade-off, the team fabricated multifunctional devices that could maintain high performance in both light emission and power generation. Their green- and orange-light-emitting devices, for example, simultaneously achieved a light-emission efficiency exceeding 8.5 percent and a power-conversion efficiency of about 0.5 percent, surpassing the combined performance of similar previously reported devices.
“Considering the 44 percent intrinsic emission efficiency of the green emitter and roughly 20 percent light-extraction efficiency, the obtained 8.5 percent emission efficiency indicates performance close to the theoretical limit, with virtually no electrical loss,” says Fukagawa.
The researchers also demonstrated the first multifunctional power-generating blue OLED reported worldwide, which was long deemed extremely difficult to realise. They beleive that the breakthroughs reported in this work could open up a new era of self-powered electronics, transforming the functionality and energy use of everyday devices.
“By integrating energy harvesting directly into light-emitting surfaces, we can create electronics that are far more energy efficient and convenient for users,” notes Fukagawa.
Immediate applications include self-powered displays and lighting systems. For instance, smartphone screens could harvest ambient light indoors or outdoors to charge their own battery, drastically extending the time between charges. This capability could also be integrated into visible light communication devices that generate power during the day and utilise it during the night.
“We envision a shift from single-function components to integrated all-in-one films. This could enable the widespread adoption of battery-less sensors and wearable electronics that operate autonomously by harvesting light,” concludes Fukagawa. The research team hopes their efforts contribute to the realisation of a sustainable, carbon-neutral society by increasing energy efficiency in everyday technology.
Pictured above : Schematic of a multifunctional device, with the directions of charge flow specified for the electroluminescence and photovoltaic functionalities
