High-Brightness, Broad-Spectrum White Organic Electroluminescent Device Obtained by Designing Light-Emitting Layers as also Carrier Transport Layers

In this study, we demonstrated an efficient energy level alignment technology to design a white organic electroluminescent (EL) device consisting of two light-emitting layers (EMLs) and a hole block layer. By doping green and red dopants into blue-emitting and green-emitting host materials with hole and electron transport abilities, respectively, the two EMLs are designed as also hole and electron transport layers. Interestingly, not only the doping concentrations but also the layer thicknesses strongly influence device performance, especially the EL spectrum. After optimization, broad-spectrum white electroluminescence with maximum current efficiency of 8.02 cd/A and power efficiency of 9.33 lm/W was obtained. With increasing current density, EL efficiency decreases first and then keeps constant at about 6.0 cd/A. Therefore, this device achieves the maximum brightness as high as 35788.0 cd/m(2). At the brightness of 20000 cd/m(2), this device has the Commission Internationale de l'Eclairage (CIE) coordinates of (0.328, 0.336). With the help of energy levels and EL spectra, injection, transport, distribution, and recombination of holes and electrons in this device are investigated in detail. The presence of the EL efficiency flat zone is attributed to the synergy of improved carrier balance and the broadening of the recombination zone.