Study of Configuration Differentia and Highly Efficient, Deep-Blue, Organic Light-Emitting Diodes Based on Novel Naphtho[1,2-d]imidazole Derivatives

• Published in: Advanced functional materials 2015-08, Vol.25 (32), p.5190-5198
• Main Authors: Liu, Ming, Li, Xiang-Long, Chen, Dong Cheng, Xie, Zhongzhi, Cai, Xinyi, Xie, Gaozhan, Liu, Kunkun, Tang, Jianxin, Su, Shi-Jian, Cao, Yong
• Format: Article
• Language: English
• Subjects: blue emission; Cathodes; Derivatives; Devices; Isomers; light-emitting devices; Multilayers; Organic light emitting diodes; Voltage
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201502163

Two novel naphtho[1,2‐d]imidazole derivatives are developed as deep‐blue, light‐emitting materials for organic light‐emitting diodes (OLEDs). The 1H‐naphtho[1,2‐d]imidazole based compounds exhibit a significantly superior performance than the 3H‐naphtho[1,2‐d]imidazole analogues in the single‐layer devices. This is because they have a much higher capacity for direct electron‐injection from the cathode compared to their isomeric counterparts resulting in a ground‐breaking EQE (external quantum efficiency) of 4.37% and a low turn‐on voltage of 2.7 V, and this is hitherto the best performance for a non‐doped single‐layer fluorescent OLED. Multi‐layer devices consisting of both hole‐ and electron‐transporting layers, result in identically excellent performances with EQE values of 4.12–6.08% and deep‐blue light emission (Commission Internationale de l'Eclairage (CIE) y values of 0.077–0.115) is obtained for both isomers due to the improved carrier injection and confinement within the emissive layer. In addition, they showed a significantly better blue‐color purity than analogous molecules based on benzimidazole or phenanthro[9,10‐d]imidazole segments. Novel naphtho[1,2‐d]imidazole derivatives are developed as light‐emitting materials for OLEDs. 1H‐naphtho[1,2‐d]imidazole based compounds exhibit a significantly superior performance than their isomeric counterparts in the single‐layer devices owing to the much higher electron injection ability directly from the cathode. However, in the multi‐layer devices, uniformly high efficiencies are obtained with a desirable bluecolor that is more pure than that of their benzimidazole and phenanthro[9,10‐d]imidazole analogues.