High-Efficiency Green Phosphorescent Organic Light-Emitting Diode Based on Simplified Device Structures **Supported by the Nanjing University of Telecommunication and Posts under Grant No NY212010, the National Natural Science Foundation of China under Grant Nos 91233117, 50973104 and 51333007, the Natural Science Fund of Jiangsu Province under Grant No BK2012834, the National Basic Research Program of China under Grant No 2015CB932200,

Abstract

A high-efficiency green phosphorescent organic light emitting diode with a simplified structure is achieved that is free of a hole transport layer. The design of this kind of device structure not only saves the consumption of organic materials but also greatly reduces the structural heterogeneities and effectively facilitates the charge injection into the emissive layer. The resulting green phosphorescent organic light-emitting diodes (PHOLEDs) exhibit higher electroluminescent efficiency. The maximum external quantum efficiency and current efficiency reach 23.7% and 88 cd/A, respectively. Moreover the device demonstrates satisfactory stability, keeping 23.7% and 88 cd/A, 22% and 82 cd/A, respectively, at a luminance of 100 and 1000 cd/m2. The working mechanism for achieving high efficiency based on such a simple device structure is discussed correspondingly. The improved charge carrier injection and transport balance are proved to prominently contribute to achieve the high efficiency and great stability at high luminance in the green PHOLEDs.