Highly efficient non-doped organic light emitting diodes based on phenanthreneimidazole derivatives with hot exciton mechanism

Organic light-emitting diodes (OLEDs) promise many advantages for next-generation illumination and future display applications. Developing organic metal-free fluorescent emitter with wide bandgap and high efficiency is both significant and challenging in OLEDs. Here, phenanthroimidazole (PI) unit possessing ultraviolet emission is connected with biphenyl, diphenylmethane and diphenyl ether moieties to construct a series of blue luminogens of PPIDPh, PPIDPhC and PPIDPhO with hot exciton character. PPIDPh with biphenyl substituent at C2 position of PI group exhibits emission peak at 454 nm in non-doped film. The integration of diphenylmethane and diphenyl ether units with PI group in PPIDPhC and PPIDPhO further limits the π-conjugation owing to sp3 hybridized carbon atom and oxygen atom, which results in bluer emission peaking at 433 nm and 437 nm in the aggregated state, respectively. Particularly, the maximum external quantum efficiency (EQEmax) of PPIDPh-based non-doped OLED reaches 10.33 % with CIE coordinates of (0.15, 0.10) and subtle efficiency roll-off of only 7.4 % at high brightness of 1000 cd m−2. The PPIDPhC and PPIDPhO-based non-doped devices display even better color purity with high EQEmax of 8.56 % and 7.90 %, Commission Internationale de ĺEclairage (CIE) coordinates of (0.17, 0.08) and (0.16, 0.08), respectively, matching well with National Television Standards Committee (NTSC) requirement for saturated blue color. Such result is among the best outcomes of non-doped blue fluorescent OLEDs with the same emission color. This result will also shed light on the further development of efficient organic wide bandgap emitter and corresponding high-performance OLED.