In conventional designs, light emission and power generation place conflicting demands on excitons, which are bound pairs of electrons and positively charged holes. Efficient electroluminescence requires excitons to recombine tightly to produce photons, while efficient photovoltaic action requires excitons to dissociate rapidly into free charges that can be collected as electrical current. This trade off has long been viewed as a fundamental barrier to realizing high performance dual function organic devices.
A team led by Professor Hirohiko Fukagawa from the Center for Frontier Science at Chiba University, Japan, addressed this problem by engineering the energy states of excitons with multiple resonance thermally activated delayed fluorescence materials. In a paper published online in Volume 17 of Nature Communications on December 7, 2025, they describe how carefully selected MR TADF compounds, used as both light emitters and light absorbers, form donor acceptor interfaces with unusually low exciton binding energies.
Exciton binding energy, Eb, measures how tightly the electron and hole are bound together at the molecular level. By tuning the material system so that Eb becomes small at the donor acceptor interface, the researchers achieved devices with minimal voltage loss and nearly ideal power generation behavior, while still maintaining strong light emission. Professor Fukagawa notes that devices with smaller Eb show very little electrical loss, supporting efficient photovoltaic operation.
The team also exploited control over Eb to tune the emission color produced by the devices. When Eb remained relatively large, the devices emitted yellow light originating from charge transfer excitons, in which the electron and hole occupy neighboring molecules across the donor acceptor boundary. When Eb was reduced, the emission switched to blue light from the MR TADF donor itself, allowing color control by adjusting the interface composition.
By optimizing the interfacial materials and their energy levels, the researchers fabricated green and orange emitting multifunctional devices that kept high performance in both operating modes. These devices reached external quantum efficiencies for light emission above 8.5 percent while maintaining power conversion efficiencies around 0.5 percent, outperforming earlier reports of similar dual function structures. According to Professor Fukagawa, taking into account the intrinsic 44 percent emission efficiency of the green emitter and an estimated 20 percent light extraction efficiency, the observed 8.5 percent device efficiency approaches the theoretical limit with almost no electrical loss.
In addition, the group demonstrated what they describe as the first power generating blue OLED with multifunctional capability. Achieving blue emission while also extracting usable electrical power has been considered especially challenging, so this result marks an important milestone in multifunctional organic optoelectronics.
The team envisions a new generation of self powered electronics that integrate energy harvesting directly into light emitting surfaces. Potential near term applications include display panels and lighting tiles that recover energy from ambient illumination, such as smartphone screens that contribute to charging their own batteries indoors or outdoors. The same approach could support visible light communication systems in which panels generate power during bright conditions and then use the stored energy to transmit data at night.
Looking ahead, the researchers see their design strategy as a step toward fully integrated films that combine several electronic and photonic functions in a single organic stack. Such all in one layers could enable battery less sensors and wearable devices that operate autonomously by harvesting light from their surroundings. The group also links this concept to the broader goal of a carbon neutral society, in which improved energy efficiency in everyday electronics helps reduce overall power demand.
The study, titled "A pathway to coexistence of electroluminescence and photovoltaic conversion in organic devices," lists authors Taku Oono, Yusuke Aoki, Tsubasa Sasaki, Haruto Shoji, Takuya Okada, Takahisa Shimizu, Takuji Hatakeyama, and Hirohiko Fukagawa from Japanese institutions including NHK Science and Technology Research Laboratories, Tokyo University of Science, Kyoto University, and Chiba University. The authors report that they have no competing interests.
The project received support from the Japan Science and Technology Agency through the CREST program under grant number JPMJCR22B3, and from the Japan Society for the Promotion of Science KAKENHI program under grant number 24K23071. The work illustrates how targeted public investment in advanced optoelectronic materials can accelerate the emergence of practical multifunctional devices.
Research Report:A pathway to coexistence of electroluminescence and photovoltaic conversion in organic devices
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