Solution-Processed Phosphorescent Organic Light-Emitting Diodes with Ultralow Driving Voltage and Very High Power Efficiency

Abstract

To realize power efficient solution-processed phosphorescent organic light-emitting diodes (s-PhOLEDs), the corresponding high driving voltage issue should be well solved. To solve it, efforts have been devoted to the exploitation of novel host or interfacial materials. However, the issues of charge trapping of phosphor and/or charge injection barrier are still serious, largely restraining the power efficiency (PE) levels. Herein, with the utilization of an exciplex-forming couple 4, 4', 4″-tris[3-methylphenyl(phenyl)amino]triphenylamine (m-MTDATA) and 1,3,5-tri(m-pyrid-3-yl-phenyl)benzene (TmPyPB), the efficient charge injection and transporting, barrier-free hole-electron recombination for the formation of the interfacial exciplex, and elimination of charge traps of phosphors in the emissive layer are realized simultaneously, resulting in a turn-on voltage of 2.36 V, a record high PE of 97.2 lm W(-1), as well as extremely low driving voltage of 2.60 V at 100 cd m(-2), 3.03 V at 1000 cd m(-2) and 4.08 V at 10000 cd m(-2). This report is the first time that the PE performance of s-PhOLED approaches 100 lm W(-1) high level, even superior to the corresponding state-of-the-art performance of the same color vacuum-deposited PhOLED (v-PhOLED) counterpart. We anticipate this report opens a new avenue for achieving power efficient monochromatic and white s-PhOLEDs with simple structures.

Figure 1. Device operating mechanism and molecular structures.

(a) The proposed device operating mechanism including I: effective hole injection and transporting; II: effective electron injection and transporting; III: barrier-free hole-electron recombination for the formation of exciplex; and IV: energy transfer from interfacial exciplex to phosphor; (b) Molecular structures of functional materials used.

Figure 2. Photophysical characteristics of different samples.

Normalized PL spectra of m-MTDATA, TmPyPB, and m-MTDATA:TmPyPB (1:1, mol/mol) blended films, together with normalized EL spectrum of m-MTDATA/TmPyPB bilayer device.

Figure 3. Performance characteristics of solution-processed OLEDs.

Current density-voltage (a), Luminance-voltage (b), Current efficiency-luminance (c) and Power efficiency-luminance (d) characteristics for device A (1 wt.% Ir(Flpy-CF₃)₃) and B (1 wt.% Ir(Flpy-CF₃)₃).

Figure 4. Current density-voltage characteristics of different devices.

device A (0 wt.% and 1 wt.% Ir(Flpy-CF₃)₃) (a), and device B (0 wt.% and 1 wt.% Ir(Flpy-CF₃)₃) (b).