Photon-upconverters for blue organic light-emitting diodes: a low-cost, sky-blue example.

In the research ecosystem's quest towards having deployable organic light-emitting diodes with higher-energy emission ( e.g. , blue light), we advocate focusing on fluorescent emitters, due to their relative stability and colour purity, and developing design strategies to significantly improve their efficiencies. We propose that all triplet-triplet annihilation upconversion (TTA-UC) emitters would make good candidates for triplet fusion-enhanced OLEDs ("FuLEDs"), due to the energetically uphill nature of the photophysical process, and their common requirements. We demonstrate this with the low-cost sky-blue 1,3-diphenylisobenzofuran (DPBF). Having satisfied the criteria for TTA-UC, we show DPBF as a photon upconverter ( I th 92 mW cm -2 ), and henceforth demonstrate it as a bright emitter for FuLEDs. Notably, the devices achieved 6.5% external quantum efficiency (above the ∼5% threshold without triplet contribution), and triplet-exciton-fusion-generated fluorescence contributes up to 44% of the electroluminescence, as shown by transient measurements. Here, triplet fusion translates to a quantum yield ( Φ TTA-UC ) of 19%, at an electrical excitation of ∼0.01 mW cm -2 . The enhancement is meaningful for commercial blue OLED displays. We also found DPBF to have decent hole mobilities of ∼0.08 cm 2 V -1 s -1 . This additional finding can lead to DPBF being used in other capacities in various printable electronics.