| United States Patent | 9,666,822 | | Forrest , et al. | May 30, 2017 |
Extended OLED operational lifetime through phosphorescent dopant profile management
Abstract This disclosure relates, at least in part, an organic light emitting device, which in some embodiments comprises an anode; a cathode; a first emissive layer disposed between the anode and the cathode, the first emissive layer comprising an electron transporting compound and a phosphorescent emissive dopant compound; and wherein the phosphorescent emissive dopant compound has a concentration gradient, in the emissive layer, which varies from the cathode side of the first emissive layer to the anode side of the emissive layer.
"In summary, we demonstrate a ten-fold increase in blue PHOLED lifetime employing an extended exciton formation zone achieved by grading the concentration profile of the hole conducting phosphorescent dopant in the EML. Considering the different color sub-pixel luminances used in displays, the improved blue PHOLED lifetimes achieved in stacked devices approaches that of green PHOLEDs under normal operating conditions. The novel device architecture employed is based on a fundamental physical understanding of the relationship between energy-driven triplet-polaron annihilation and device degradation, and hence should be generally applicable to a wide range of phosphorescent and fluorescent devices. Further lifetime improvements are anticipated by finding dopant/host combinations with conduction properties similar to the materials used here, and that minimize interactions between triplets on the dopant and polarons on the host molecules, therefore decreasing the probability of occurrence for high energy TPA interactions that lead to molecular decomposition, and hence loss of luminance over time." |
