OLED Emitting Layer Stack for Higher Efficiency and Longer Lifetime

The light-emitting layer is divided into multiple sub-layers (first light-emitting layer, second light-emitting layer, third light-emitting layer) with different functions. Each layer contains specific host-guest material combinations optimized for particular purposes: the first layer uses TADF host materials with narrow-band guest materials for high efficiency, the second layer uses fluorescent host materials for color emission, and the third layer uses phosphorescent host materials for additional light output. This segmentation allows each layer to be optimized independently for its specific function, achieving high luminous efficiency while managing complexity through functional specialization.

The patent introduces a vertical dimension to energy transfer by stacking multiple light-emitting layers with different energy transfer mechanisms. The first light-emitting layer utilizes TADF (thermally activated delayed fluorescence) for efficient triplet exciton utilization, the second layer employs fluorescent energy transfer, and the third layer uses phosphorescent energy transfer. This multi-dimensional approach to energy transfer allows the device to harvest both singlet and triplet excitons effectively across different layers, converting what would be lossful exciton annihilation into useful light emission through diversified energy transfer pathways.

The patent applies different guest material characteristics to different local regions (layers) of the device. The first light-emitting layer uses narrow-band guest materials (such as BPhen, Bpy-OXD) specifically where TADF energy transfer occurs, achieving high color purity. The second and third layers use different guest materials optimized for fluorescent and phosphorescent energy transfer respectively. This local optimization allows each layer to achieve both color purity and energy transfer efficiency appropriate to its specific energy transfer mechanism, rather than requiring a single compromise solution across the entire device.