Towards high-power-efficiency solution-processed OLEDs: Material and device perspectives

Solution-processed organic light-emitting diodes (s-OLEDs) have received a great deal of interest owing to the huge market application potentials as large-size, flexible, high-quality self-luminous display panels and lighting sources. It is anticipated that those electronic products can be easily manufactured by modern wet-processing techniques, e.g. ink-jet printing and 'roll-to-roll' coating methods. However, issues related to power efficiency (PE) are highly hampering the progress of s-OLEDs towards real applications. Herein, we will demonstrate current development of s-OLEDs targeting for high PE with emphasis on introducing (i) theoretical and practical significance in simultaneously achieving close-to-unity (similar to 100 %) exciton emission and low driving voltage realized by advanced interface modification, bipolar-transporting-type host, all-exciton-harvesting emissive material and customized device architectures to integrate their functions, (ii) novel low-driving-voltage techniques for phosphorescent and thermally activated delayed fluorescence (TADF) s-OLEDs, i.e. barrier-free exciplex host or bipolar co-host scaffold, and charge-trapping- or charge-scattering-free emissive layer (EML) structures by matching the frontier molecular orbitals (FMOs) between host and dopant emitters, (iii) a variety of tactics to effectively alleviate the efficiency roll-off issue at the practically high luminance value, e.g. removing or largely restraining exciton-quenching in the EML and/or interfaces, the utilization of novel emitters with fast radiative decay rate and/or the EML architectures with prompt and efficient Forster energy transfer process.