A host–guest system comprising high guest concentration to achieve simplified and high-performance hybrid white organic light-emitting diodes†
Single-emitting-layer (single-EML) hybrid white organic light-emitting diodes (WOLEDs) have attracted a great deal of attention due to their simplified structures. However, the guest concentration is usually too low, which is quite difficult to control and reproduce in the coevaporation process. Herein, for the first time, N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine has been used as both the host and the blue emitter in single-EML WOLEDs. By dint of this multifunctional material, the concentration is found to be as high as 1.5%. This device exhibits a maximum total efficiency of 65.3 lm W−1, indicating a significant step towards the real commercialization. Besides, low voltages (i.e., the turn-on voltage is 2.4 V and 3.45 V at 1000 cd m−2) and a color rendering index (CRI) of 77 are obtained for this two-color WOLED. Unlike the working mechanisms in previous single-EML hybrid WOLEDs with low guest concentrations, devices comprising high concentrations exhibit more sophisticated engineering, in which the device smartly allows the utilization of both the fluorescence from the host itself, and the complementary phosphorescence from the guest by incomplete Förster energy transfer, Dexter energy transfer as well as direct exciton formation on the guest. Moreover, we have incorporated this unique host–guest system into a dual-EML hybrid WOLED. Maximum efficiencies of 17.2 lm W−1 and 10.2 lm W−1 at 1000 cd m−2 (3.85 V) with an ultrahigh CRI of 93 are achieved, providing a new opportunity to accomplish the simplified structure/low voltage/high efficiency/ultrahigh CRI trade-off.