Reviewed by Lexie CornerJun 2 2025
Researchers at Kyushu University have developed a new analytical model to describe the kinetics of exciton dynamics in OLED materials. Their findings, published in Nature Communications, may help improve the lifespan of OLED displays and support the development of more efficient materials.
Excitonic energy configuration changes of a TADF material. Excitonic state alignment is affected by temperature and the solvent the material is in. This leads the peculiar exciton kinetics when the energy gap between S1 and T1 approaches to zero. Image Credit: Chihaya Adachi, Youichi Tsuchiya/Kyushu University
Organic light-emitting diodes (OLEDs) are photoluminescent devices that use organic molecules to produce light. Compared to conventional LEDs, OLEDs can be more efficient, are compatible with thin and flexible materials, and provide a wider range of image contrast. Researchers around the world are studying the underlying chemistry and physics of OLEDs to further improve their performance.
OLEDs emit light through a process involving excited electrons, known as excitons. When energy is added to an atom, its electrons move to a higher energy level. As they return to their original state, they release energy as fluorescence. Excitons can exist in two forms: a singlet state (S1) and a triplet state (T1). Fluorescence occurs only when excitons return from the singlet state.
Thankfully, excitons can transfer between the triplet and singlet states. Therefore, if we can convert triplet excitons into singlets, the efficiency of fluorescence drastically improves. One of the major breakthroughs of OLED research was in the development of thermally activated delayed fluorescence, or TADF, materials. These materials would close the ‘gap’ between S1 and T1, so that T1 excitons more easily transfer to S1, thus producing more fluorescence.
Chihaya Adachi, Study Lead and Professor, Center for Organic Photonics and Electronics Research, Kyushu University
Understanding the difference between S1 and T1 in TADF states in TADF materials is important for evaluating OLED efficiency and testing new materials. However, traditional methods for measuring this energy gap can be unreliable due to subjective interpretations and underlying assumptions.
When developing new TADF materials, we employ quantum calculations to forecast this gap, denoted as ΔEst. However, it is not feasible to theoretically calculate the behavior of all electrons to determine the accurate excitation state configuration. So, to reduce computation costs, we usually work with certain assumptions. But this results in different values between experimental and estimated data.
Youichi Tsuchiya, Study First Author and Research Associate Professor, Kyushu University
Tsuchiya said, “To close the gap between theoretical and experimental methods, our team worked to develop a model that can more accurately estimate ΔEst. Our new analytical method employed several fundamental theories of physical chemistry and put into account the exciton transfer between the triplet energy states.”
Until now, accurately describing the excited-state structures of organic compounds has been a challenge. The researchers expect their findings to support the development of high-performance light-emitting materials and contribute to future advances in photochemistry.
Adachi added, “This new analytical method will be utilized on other types of TADF materials as well, helping us to clarify exciton dynamics in future OLED research. We also want to explore the use of AI to accurately predict the properties of new materials.”
Journal Reference:
Tsuchiya, Y., et al. (2025) Temperature dependency of energy shift of excitonic states in a donor–acceptor type TADF molecule. Nature Communications. doi.org/10.1038/s41467-025-59910-z.