posted on 2020-02-05, 21:45authored byJinhyo Hwang, Chiho Lee, Ji-Eun Jeong, Chae Yeong Kim, Han Young Woo, Sungnam Park, Min Ju Cho, Dong Hoon Choi
Recently,
various host materials have been developed for solution-processed
thermally activated delayed fluorescent organic light-emitting diodes
(TADF-OLEDs). Compared with small-molecule hosts, polymeric hosts
are advantageous for inducing a uniform distribution and segregation
of dopant molecules in the emissive layer without undesired large-scale
phase separation. In this study, new polymer hosts were demonstrated,
in which a bipolar conjugative moiety consisting of a carbazole (Cz)
donor and an α-carboline (α-Cb) acceptor was bound to
the polystyrene backbone through a non-conjugated linker. They exhibited
high triplet energies of >2.8 eV, and their emission spectra overlapped
with the absorption spectrum of a green TADF emitter, which allowed
facile energy transfer from the polymeric host to the small-molecule
dopants. High device performance was observed, with external quantum
efficiencies (EQEs) of 13.65, 17.09, and 17.48% for solution-processed
green TADF-OLEDs using PSCzCz, PSCzCb, and PSCbCz, respectively, as hosts for the EML. The EQEs of bipolar
host (PSCzCb and PSCbCz)-based devices were
higher than those of unipolar host (poly(N-vinylcarbazole)
and PSCzCz)-based devices owing to the well-balanced
charge-carrier transport. According to these results, the polymeric
host bearing a bipolar Cz and α-Cb coupled moiety is a promising
material for solution-processable TADF-OLEDs.