High color rendering index white organic light-emitting diodes based on a polymer-small-molecule excited system

Developing structurally simple, low-cost, and solution-processable white organic light-emitting diodes (WOLEDs) with a high color rendering index remains a challenge. Herein, a dye-free WOLED is developed based on a novel, to the best of our knowledge, polymer-small-molecule system constructed of poly(N-vinylcarbazole) (PVK) and 2-(9,9'-spirobi[fluoren]-3-yl)-4,6-diphenyl-1,3,5-triazine (SF3-TRZ). The device exhibits high-quality white electroluminescence originating from complementary emissions of the bluish-green PVK: SF3-TRZ exciplex and the electromer of SF3-TRZ. By further inserting a 4,4'-bis(9-carbazolyl)-2,2'-dimethylbiphenyl (CDBP) layer into the emission layer, a deep-blue CDBP/SF3-TRZ interfacial exciplex is formed to generate additional reverse intersystem crossing (RISC) channels, which further improve the performance of WOLED. Consequently, the optimized WOLED achieves broadband white emission with CIE coordinates of (0.32, 0.33) at 8 V and a high color rendering index (CRI) of 93. It delivers peak current and power efficiencies of 8.32 cd/A and 7.70 lm/W, respectively. This work paves the way for high-quality WOLED with simple architecture and low-cost fabrication.