Power-efficient and solution-processed red phosphorescent organic light-emitting diodes by choosing combinations of small molecular materials to form a well-dispersed exciplex co-host

Abstract

Intrinsic compatibility of exciplex couple determines the EL performance of the resultant solution-processed phosphorescent OLEDs, particularly driving voltage behaviours.

Recent Advances in Conjugated TADF Polymer Featuring in Backbone‐Donor/Pendant‐Acceptor Structure: Material and Device Perspectives

“…Physical blending with extra charge‐transport‐type matrix was applied but it brought very little and even adverse effect . Except for explains by thermodynamic and kinetics multi‐component incompatibility problems during solution‐process, other uncertainties may be involved in these complex systems . It is thus expected to explore an “upgraded” conjugated TADF polymers by chemical engineering, i. e. simultaneously with high Φ PL /Φ DF and efficient‐/bipolar‐ charge transport superiorities.…”

“…However, since this geometry essentially interrupts the conjugation of the backbone, it belongs to nonconjugated type, which is not good for charge transport of the polymer emitters. Towards low‐voltage driving and power‐efficient s‐OLEDs, it thus needs to combine other excellent charge‐transport matrix to disperse it, which is complex and might arise other issues, such as phase separation …”

Recent Applications of Interfacial Exciplex as Ideal Host of Power-Efficient OLEDs

“…By contrast, s-PhOLEDs using bulk exciplex of m-MTDATA:TmPyPB (1:1 w/w) was unsatisfied, corresponding to a low PE max. of 35.2 lm W −1 mainly due to sharply increased driving voltages, e.g., V on /V 100 /V 1000 : 4.15/5.18/5.80 V. Two reasons were involved; i) low charge transporting capability of the bulk exciplex couple due to their intrinsic incompatibility (Yao et al, 2018); ii) the serious charge trapping tendency of dopant in the EML structure of m-MTDATA:TmPyPB:dopant (Wang et al, 2015). Accordingly, interfacial exciplex rather than bulk exciplex shown here is more suitable for s-PhOLEDs as a host.…”

Effect of PEDOT:PSS on the performance of solution-processed blue phosphorescent organic light-emitting diodes with an exciplex host

“…11 The majority of exciplex blend host studies have focussed on films that are deposited by vacuum evaporation with there being few reports of solution processed exciplex host-based OLEDs. 12,13 While the creation of exciplex host blends for green and red guest emitters is relatively straightforward, it is more difficult to create donor-acceptor combinations that form suitable hosts for blue emissive materials, 14 and in particular, solutionprocessed blue phosphorescent emitters. The emission energy of the exciplex host is governed by the ionisation potential of the donor and the electron affinity of the acceptor and hence there needs to be a sufficiently large energy offset such that neither component of the exciplex host nor the formed exciplex quench the triplet state of the blue emitter.…”