Biography
Prof. Dashan Qin
Prof. Dashan Qin
Hebei university of technology, China
Title: Reducing power loss in p-i-n organic light emitting diodes: an attempt to advance towards the thermodynamic limit
Abstract: 

Organic light emitting diodes (OLEDs) have been moving fast towards the commercialization during the past decades, because of their appealing merits such as easy fabrication, flexibility, low weight, etc. The OLEDs based on p-i-n concept have been successfully made small- to medium-sized flat-panel displays widely used in mobile phones. However, the TVs and lighting panel based on the modern OLED technology are still suffering from fast aging, high cost, and image retention. Therefore, it is of great importance to improve the performance of p-i-n OLEDs well established as the quasi-standard technology of OLED industry. 

Like GaN LEDs, a good OLED must be a good diode featuring low power loss, i.e., low thermal generation. The electro-thermal effect is a major factor leading to the degradation of OLED especially at high luminance. For state-of-art p-i-n OLEDs, the heat is generated in emissive layer due to its large series resistance; in addition, the heat is also created in the p-doped and n-doped layers. At a given practical luminance, e.g., 500 cd/m2, the voltage drops over p- and n-doped transport layers are comparable to that over emissive layer [1]. Thus, it is worth investigating the power loss caused by p- and n-doped transport layers. In general, there are three kinds of hole (power) losses incurred in p-i-n OLEDs, i.e., the injection loss from ITO to p-doped layer, conduction loss through p-doped layer, and interfacial loss from p-doped layer to electron blocking layer. It has been demonstrated that the usage of a single p-doped layer is unable to optimize these hole losses simultaneously [2]. The similar case is also found for using a single n-doped transport layer [3].  

In this speech, I will talk of the influences of the HOMO level of p-type host, p-dopant type, and p-doping profile on the hole losses, and then point out that the combination of multi-p-doped layers outperforms any single p-doped layers in both fluorescent and phosphorescent OLEDs. Also, I will show the combined n-doped layers outperform single n-doped layers. Hopefully, the p- and n-doping structures proposed here can advance OLEDs into the TV and lighting applications in a cost-effective way.