The intrinsic limitation of OLEDs arises from the fact that only 25% of electronically excited states can directly contribute to light emission. The remaining 75% reside in triplet states, which typically undergo non-radiative decay, reducing overall efficiency. New research explores how strong light-matter coupling in OLEDs can create novel quantum states known as polaritons, which can significantly enhance brightness by unlocking previously inaccessible triplet states.
The researchers introduce a theoretical model demonstrating how polaritons can facilitate triplet-to-singlet conversion through reverse inter-system crossing (RISC) and triplet-triplet annihilation (TTA). This process is made possible by microcavity-enhanced strong coupling, which alters the energetic landscape of excited states in OLEDs.
Polaritonic RISC enhancement occurs when placing a cavity mode in resonance with the singlet state, significantly increasing the efficiency of RISC, thereby converting triplet excitons into emissive singlets. This transition is governed by Fermi’s golden rule and Marcus theory of electron transfer, which describe how energy levels and reorganization energies influence the transition rate. Polaritons also impact TTA, an alternative triplet harvesting mechanism where two triplet excitons interact to form a singlet state that can emit light. The theoretical model shows that under optimal conditions, polaritonic states can accelerate TTA, further increasing OLED brightness. The study also explores how strong coupling can reduce SSA, a competing process that can cause efficiency roll-off in OLEDs. By delocalizing singlet excitons, polaritons can effectively reduce the probability of SSA, prolonging device lifespan.
While the theoretical model provides strong evidence for the benefits of polaritons in OLEDs, practical realization remains challenging due to material constraints. The formation of polaritonic states depends on finding organic materials with strong oscillator strengths and stable cavity-mode coupling. Identifying such materials is a crucial step in experimental validation. The microcavity must be precisely designed to match the energy levels of singlet and triplet states, requiring advanced fabrication techniques. While triplets are generally non-emissive, their interaction with polaritons must be finely tuned to ensure optimal harvesting without excessive loss through non-radiative channels.
The integration of polaritons into OLEDs presents a promising strategy for significantly enhancing their brightness and efficiency. Theoretical models suggest that microcavity-enhanced strong coupling can unlock new pathways for triplet utilization, thereby overcoming the 25% singlet emission limitation. However, experimental validation is required to translate these theoretical predictions into commercial applications. Future research should focus on developing new organic materials with optimized coupling properties and refining cavity designs to maximize efficiency.
By bridging fundamental quantum mechanics with practical OLED engineering, this study paves the way for next-generation high-performance optoelectronic devices.
Reference
O. Siltanen, K. Luoma, A. J. Musser, K. S. Daskalakis, Enhancing the Efficiency of Polariton OLEDs in and Beyond the Single-Excitation Subspace. Adv. Optical Mater. 2025, 2403046. https://doi.org/10.1002/adom.202403046
