NHK’s Science & Technology Research Laboratories (STRL) says it has developed an organic light-emitting display element that can switch between emitting light and generating electricity, including blue emission – a key step for full-colour display applications.
The work, carried out with researchers at Chiba University and Kyoto University, has been reported in Nature Communications in a paper describing a “pathway to coexistence of electroluminescence and photovoltaic conversion in organic devices”.
The challenge, researchers note, is that electroluminescence (turning electricity into light) and photovoltaic conversion (turning light into electricity) are essentially opposite processes. Device architectures and material choices that optimise one typically compromise the other.
In the Nature Communications study, the team outlines a strategy based on multiple-resonance thermally activated delayed fluorescence (MR-TADF) materials, paired with device-level control of charge-transfer states at donor/acceptor interfaces. The paper reports visible electroluminescence spanning blue through red, as well as white emission, while maintaining charge generation needed for photovoltaic operation.
Performance metrics highlighted in the paper point to progress on both sides of the trade-off. The authors report an external quantum efficiency (EQE) exceeding 8.5% for green and orange emitting devices, alongside a power conversion efficiency (PCE) of around 0.5% when operated for photovoltaic generation.
NHK is positioning the breakthrough around resilience and low-power use cases, arguing that a display capable of harvesting ambient light could help extend operation where mains power is unavailable. Researcher Taku Oono linked the motivation to the loss of access to critical information during the Great East Japan Earthquake. “Speaking on behalf of the development team, NHK researcher Taku Oono shared the motivation behind this innovation: “During the Great East Japan Earthquake, many people evacuated to places like school rooftops. “Over time, they lost access to critical information because there was no electricity. Although NHK broadcast vital updates, some of the people who needed them most couldn’t receive them. In the future, we hope this technology can be applied to devices such as mobile screens, so that even in places without electricity, everyone can access the information they need.”
In practical terms, the concept is a screen element that can be driven to emit as a display, then alternate into a generation mode to recover some energy from light. The researchers also point to future “self-powered displays and lighting” as potential application areas if efficiencies and durability can be improved and the approach scaled beyond laboratory prototypes.
For NHK STRL, the project also sits alongside broader work on next-generation display formats, including more flexible and deformable screen concepts. The group says its next phase will focus on improving both efficiency and operational lifetime in each mode – light emission and power generation – to move closer to deployable low-power display devices.
