High-performance warm-white OLEDs using interfacial exciplex energy transfer with external quantum efficiency exceeding 30%

Abstract

To achieve energy-saving and environmentally friendly warm white lighting through the simplification of white organic light-emitting device (WOLED) structure and manufacturing process, we designed and optimized a WOLED by incorporating bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III)(FIrpic)-doped 4,4′,4′-tris(N-carbazolyl)triphenylamine(TCTA) and bis(4-phenylthieno[3,2-c]pyridinato-N,C2')(acetylacetonate)iridium(III)(PO-01)-doped 2,2',2′'-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)(TPBI) thin films as the blue and yellow emissive layer (EML), respectively, and forming an exciplex at TCTA and TPBI interface. By adjusting the doping concentration and position within the EML and the thickness of the transport layer, we achieved the optimal emission balance between the blue and yellow colors in the proposed WOLED. We successfully fabricated a highly efficient and structurally simplified WOLED without the use of light extraction coupling techniques, which exhibited high external quantum efficiency (EQE) of 32.6% and current efficiency (CE) of 80.3 cd/A, along with stable emission color with minimal CIE variation of ΔCIE(0.0027, 0.0023) from 500 cd/m² to 5000 cd/m². The experimental results revealed that the designed device structure with the triple host system (TCTA, TPBI, and interface exciplex) facilitated the widening of the recombination zone (RZ), enhanced exciton confinement and utilization, reduced triplet-triplet annihilation (TTA) effects, and achieved efficient host-guest energy transfer. Furthermore, the designed WOLED emitted warm white light spectrum suitable for healthy lighting applications. Therefore, we believe that our work contributes to the further development of ideal and simplified WOLED structure designs for achieving high-efficiency, simplified manufacturing, low-cost, energy-saving, and environmentally friendly healthy lighting.