Organic light-emitting diodes (OLEDs) have promising applications in displays, lighting, communication, and medical treatments. The successful commercialization of foldable OLED smart phones attracts global interest on organic semiconductors. Unlikely the inorganic counterparts, e.g., Si, Ge, and GaAs, organic semiconductors are typically amorphous, flexible, light, and even transparent.
Researchers led by Prof. Guohua Xie at Wuhan University (WHU), China, are interested in OLEDs, where the light is generated at the thin film with a thickness of ca. 100 nm. The conventional fluorescent materials, either small molecules or polymers, tend to quenched at the condensed state. In addition, 75% of the energy will be lost and turned into useless heat under electroluminescence since triplet excitons of fluorescent materials are non-radiative. To address these drawbacks, a host with both unique properties of aggregation-enhanced emission and thermally activated delayed fluorescence (TADF) which could harvest all the electrically generated excitons was introduced to design the solution-processed OLEDs by spin-coating. It is verified that the TADF host efficiently and universally sensitized the fluorescent polymers and reduced the concentration quenching at the aggregated states, which resulted in the dramatical improvement of external quantum efficiency by a factor up to 13.8. The work entitled “Thermally activated delayed fluorescent small molecule sensitized fluorescent polymers with reduced concentration-quenching for efficient electroluminescence” was published on Frontiers of Optoelectronics (published on Mar. 21, 2023).