Hyper Triplet-Triplet Fusion Blue Fluorescent Organic Light-Emitting Diode

Triplet is like a double-edged knife, that can degrade or benefit the electroluminescence performances of organic light-emitting diodes (OLEDs), especially for blue light. Therefore, efficient triplet harvesting for triplet-triplet fusion (TTF) fluorescence emission is essential to achieving high-efficiency blue TTF-OLEDs, which are known for their excellent reliability. This study presents a hyper-TTF mechanism for maximizing triplet exciton usage and avoiding triplet-polaron quenching to generate more photons through Dexter energy transfer (DET) and TTF processes. Specially, a triplet tank layer (TTL) was introduced adjacent to the TTF emitting layer (EML). Efficient carrier recombination and triplet generation are confined to the TTL of the device. Most triplets were observed to undergo DET from the TTL to the TTF EML; they subsequently became singlets exhibiting delayed fluorescence. Furthermore, the triplet-polaron quenching is suppressed by inhibiting hole into the TTF EML. A record-high TTF-OLED efficiency was achieved with an external quantum efficiency of 15.4%.