Reverse Intersystem Crossing and Exciton Harvesting: A Pathway to Low Threshold in Multi‐Resonant TADF Electrically Pumped Organic Semiconductor Lasers

ABSTRACT If electrically pumped lasing in organic semiconductors could be achieved, it would have a wide‐ranging impact on many fields, including healthcare, information transmission, and sensing to name a few. However, a major challenge in the development of these devices is overcoming triplet accumulation that leads to the annihilation of the lasing singlet species. The utilization of triplet recycling, whereby triplets are back converted into lasing singlets has emerged as a promising strategy to address this. Herein, high‐speed micro‐OLEDs incorporating the multi‐resonant TADF emitter DABNA‐2 are found to exhibit marked performance enhancements upon introduction into a BSBCz host, which serves as an efficient triplet scavenger. This tailored host environment demonstrates a path to low‐threshold lasing devices. Using a combination of experiment and numerical modelling, we visualize the build up of the singlets/triplets/polarons within the device identifying key mechanisms that can be used to reduce the lasing threshold. Using this framework, we are able to calculate lasing thresholds for these materials and estimate how far the community is from a lasing device.