基于溶液加工小分子材料发光层的有机-无机复合发光器件

报道了基于溶液加工有机小分子材料发光层、聚乙烯亚胺电子注入层的有机-无机复合发光器件. 优化了空穴传输层和磷光染料的掺杂浓度, 得到最佳发光效率的器件. 蓝光、黄光和红光器件的最大外量子效率为17.3%, 10.7% 和7.3%. 在发光亮度为1000 cd/m² 时, 蓝光、黄光和红光器件的外量子效率分别为17.0%, 10.6% 和5.8%, 器件效率下降较小. 原因在于同时采用空穴传输型和电子传输型的小分子材料作为共同主体材料, 器件具有较宽的载流子复合区域, 降低了三线激发态-三线激发态湮灭和三线激发态-极化子相互作用对器件发光效率的影响. 白光器件在亮度为1000 cd/m²时, 发光效率和功率效率为31 cd/A和 14.8 lm/W. 器件的色度为(0.32, 0.42), 色度比较稳定, 随电流的变化微小. 器件的效率较以往报道的有机-无机复合发光器件有显著的提高, 主要归因于在聚乙烯亚胺上能够制备特性良好的小分子材料薄膜, 以及小分子主体材料拥有较高的三线态能量和平衡的载流子传输特性, 能够获得高效的磷光发射.

Phosphorescent hybrid organic-inorganic light emitting devices with solution-processed small molecule emissive layers

We report efficient phosphorescent hybrid organic-inorganic light emitting devices using poly(ethylenimine) as electron-injection layer and interfacial modifier for metal oxides and solution-processed small molecule emissive layers. As a first step, the hole transport layers with various HOMO levels and the hole mobility values including TAPC, TCTA and mCP are evaluated. The results indicate that devices using a TAPC layer show the best luminance and power efficiencies. Subsequently, the optimum phosphor concentration is determined to be ca. 5%. Enlarged efficiency roll-off with increasing current density is observed in devices using the phosphor concentration above the optimum value. We also investigate the morphologies of films having different phosphor concentrations on the top of bare or PEIE-covered glass substrates, which is closely related to device performance. All the films have the RMS values of ca. 1 nm, indicating high-quality solution processed small molecule films. The blue, yellow and red devices show the maximum external quantum efficiencies of 17.3%, 10.7% and 7.3%, respectively. These efficiencies are 17.0%, 10.6% and 5.8% at 1000 cd·m^-2, only showing a small roll-off, which can be attributed to alleviated triplet-triplet and triplet-polaron interactions in a broad carrier recombination zone due to using the mixed hole-transport and electron-transport materials as the co-hosts. In addition, these devices exhibit the respective Commission International Eclairage (CIE) coordinates of (0.16, 0.36), (0.50, 0.49) and (0.66, 0.32), which almost traverse the whole visible light region. Furthermore, the hybrid two-colored white devices show a luminance efficiency of 31 cd·A^-1, power efficiency of 14.8 lm·W^-1 at 1000 cd·m^-2 and the operating current-insensitive CIE coordinates of (0.32, 0.42). The efficiencies represent the significant improvement over the previously reported values, which can be attributed to high-quality small molecule films on PEIE, and in particular to the unique properties of small molecule host materials such as balanced carrier transport and high triplet energy. Further efforts including selection of high-mobility electron transport host material and phosphors with high luminescence quantum yield are made to increase the efficiency and reliability of hybrid organic-inorganic light emitting device.