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.

Automated summary

In this study, three new polymer hosts were developed for solution-processed narrowband blue organic light-emitting diodes (OLEDs). The non-conjugated polynorbornenes were found to have high triplet energy levels, making them suitable as host materials for blue emitters. Additionally, increasing the electron-donating capability of the side chain arylamine elevated the HOMO levels of the polymer hosts. By using a specific dopant, efficient narrowband blue electroluminescence was achieved in solution-processed OLEDs.