The thermal management issue in OLED (organic light emitting diode) devices has a significant impact on the efficiency, reliability, and life time of the device. In particular, in OLED systems with multipolar or double cathode electrodes, it is important to accurately interpret the effect of heat generated by current flow between electrodes on the emitting layer. In this study, the governing equation was established based on the heat conduction equation to mathematically model and analyze this heat distribution, and the heat distribution analysis was performed using the COMSOL program. It was confirmed that the temperature generated in the OLED with the double cathode structure reached a maximum of 343.157 K centered on the emitting layer. The heat distribution generated in the proposed OLED structure with the double cathode electrodes was confirmed to be highly distributed in the center toward the double cathode electrodes, which is believed to be because the arrangement of the double cathode electrodes improves the symmetrical distribution of temperature while reducing power consumption.

The key to determining the lifetime of OLED device is how much brightness can be maintained. It can be said that there are internal and external causes for the degradation of OLED devices. The most important cause of internal degradation is bonding and degradation in the excited state due to the electrochemical instability of organic materials. The structure of OLED modeled in this paper consists of a cathode layer, electron injection layer (EIL), electron transport layer (ETL), light emission layer, hole transport layer (HTL), hole injection layer (HIL), and anode layer on a glass substrate from top to bottom. It was confirmed that the temperature generated in OLED was distributed around the maximum of 343.15 K centered on the emission layer. It can be seen that the heat distribution generated in the presented OLED structure has an asymmetrically high temperature distribution toward the cathode, which is believed to be because the sizes of the cathode and positive electrode are asymmetric. Therefore, when designing OLED, it is believed that designing the structures of the cathode and anode electrodes as symmetrically as possible can ensure uniform heat distribution, maintain uniform luminance of OLED, and extend the lifetime. The thermal distribution of OLED was analyzed using the finite element method according to Comsol 5.2.

We have fabricated white organic light-emitting diodes (OLEDs) by co-doping of red and blue phosphorescent guest emitters into the single host layer. Tris(2-phenyl-1-quinoline) iridium(III) [Ir(phq)3]and iridium(III)bis[(4,6-di-fluorophenyl)-pyridinato-N,C2`]picolinate (FIrpic) were used as red and blue dopants, respectively. The effects of dopant concentration on the emission, carrier conduction and external quantum efficiency characteristics of the devices were investigated. The emissions on the guest emitters were attributed to the energy transfer to the guest emitters and direct excitation by trapping of the carriers on the guest molecules. The white OLED with 5% FIrpic and 2% Ir(phq)3 exhibited a maximum external quantum efficiency of 19.9% and a maximum current efficiency of 45.2 cd/A.

We have fabricated white organic light-emitting diodes (OLEDs) using several thicknesses ofelectron-transport layer. The multi-emission layer structure doped with red and blue phosphorescent guestemitters was used for achieving white emission. 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) wasused as an electron-transport layer. The thickness of BCP layer was varied to be 20, 55, and 120 nm. The current efficiency, emission and recombination characteristics of multi-layer white OLEDs wereinvestigated. The BCP layer thickness variation results in the shift of emission spectrum due to therecombination zone shift. As the BCP layer thickness increases, the recombination zone shifts toward theelectron-transport layer/emission-layer interface. The white OLED with a 55 nm thick BCP layerexhibited a maximum current efficiency of 40.9 cd/A.