Computational Evaluation with Experimental Validation: Arylamine-Based Functional Hole-Transport Materials for Energy-Efficient Solution-Processed OLEDs

Ultra-efficient and stable OLED devices can be obtained via effective charge injection, accumulation, and exciton confinement into the emissive layer. However, the leakage of charge and excitons from the EML to adjacent layers can lead to low device performance. Thus, high-triplet-energy charge-transport materials (CTMs) are required to confront these issues. Herein, we demonstrate a class of efficient arylamine derivatives, viz. TPA-Py, TPA-2Py, and DPA-2Py, which were synthesized through the insertion of triphenyl pyridine as an acceptor unit to the aryl amino system to accomplish high triplet energy, thermal stability, and charge transportability during device operation. The charge-transfer analysis of the developed materials was accomplished for the S-1 and T-1 states through theoretical simulation. The intramolecular hole reorganization energies helped in understanding the hole transportability of these molecules. Single-crystal analysis indicated a considerable dihedral angle across the units, quasiplanar geometries, and the nonexistence of pi-pi stacking in the solid state. These molecular materials exhibited good thermal stability, which improve the morphological stability of their thin films. All of the molecules possess suitable HOMO energy levels for hole injection and appropriate LUMO energy levels for electron blocking from the emissive layer. Moreover, their high triplet energy (up to 2.69 eV) prevents exciton transfer from the EML to HTL and results in better device performance. The device with DPA-2Py as an HTM in a green OLED showed the maximum current efficiency (CE) and power efficiency (PE) values of similar to 74 cd/A and similar to 72 lm/W, respectively, with a maximum EQE of similar to 21%. The PE of the current device is at par with the highest reported PE so far in solution-processed phosphorescent OLEDs.