Non-conjugated Polynorbornene Hosts with High Triplet Energy Levels for Solution-processed Narrowband Blue OLEDs

Three polymer hosts (namely PNB-tBuCz, PNB-Ac, PNB-TAc) containing non-conjugated polynorbornene (PNB) backbone and hole-transporting arylamine segments (carbazole, acridan and dendritic teracridan) in side chains are developed for solution-processed narrowband blue organic light-emitting diodes (OLEDs). It is found that the non-conjugated polynorbornenes can keep high triplet energy (ET) levels in range of 3.12–3.20 eV by interrupting the conjugation of repeating units, making them capable as host materials for blue emitters. Meanwhile, by increasing the electron-donating capability of side chain arylamine from carbazole to acridan and dendritic teracridan, the highest occupied molecular orbital (HOMO) levels for the polymer hosts are elevated from −5.50 eV to −5.11 eV, beneficial for reducing the hole injection barrier from anode to emissive layer. As a result, solution-processed OLEDs employing polynorbornenes with dendritic teracridan side chain (PNB-TAc) as host and boron, selenium, nitrogen-containing multiple resonance thermally activated delayed fluorescence emitter as dopant reveal efficient narrowband blue electroluminescence with emission peak at 474 nm, full-width at half maximum of 30 nm, together with maximum external quantum efficiency of 20.2%, representing the state-of-the-art device efficiency for solution-processed OLEDs with narrowband blue emission.