Solution-Processed Hybrid Hosts: A Way to Clinch High Triplet Energy with Admirable Current and Power Efficiency Devoiding Outcoupling Mode for Phosphorescent OLED
Host materials with maximum recombination efficiency and high triplet energy, the only optimistic prospects for high efficacy phosphorescence organic light emitting diodes (PhOLEDs), are portraying a major confront to synthesis for constraints associated with present PhOLEDs. While there exists a flood of vacuum deposited host materials, but the present need is solution processed hosts for its virtuous benefits. Herein, a library of new solution-processed donor-acceptor based highly efficient hosts, namely DT316, 309, 313, 320, 321 comprising of the electron transporting unit benzimidazole and hole transporting unit triphenylamine is developed. All the molecules possess good solubility in common organic solvents. The highly twisted conformation bestows these molecules with high thermal stability and remarkable triplet energy of 2.79-2.87 eV. The use of these new host materials as emissive layer in solution-processed green PhOLEDs with Ir(ppy)3 as emitter divulges an excellent efficacy with maximum power efficiency of 54.4 lmW-1, current efficiency of 73.1 cdA-1 and brightness of 21,880 cdm-2, while with Ir(2-phq)3 for red device depicts 25.6 lmW-1, 19.3 cdA-1, and 15,519 cdm-2, respectively, devoiding any external outcoupling techniques. The effective host-to-guest energy transfer, balanced charge carriers in the recombination zone, and the ability to generate exciton on both host and guest attribute to marvellous performance.