Minimizing Efficiency Roll-Off in Organic Emitters via Enhancing Radiative Process and Reducing Binding Energy: A Theory Insight.

Organic solid-state lasers have received increasing attention due to their great potential for realizing organic continuous-wave or electrically driven lasers. Moreover, they exhibit significant promise for optoelectronic devices due to their chemically tunable optoelectronic properties and cost-effective self-assembly traits. Recently, a great progress has been made in organic solid-state lasers via spatially separated charge injection and lasing. However, making directly electrically driven organic semiconductor lasers is very challenging. It is difficult because of a number of excitonic losses caused by the spin-forbidden nature as well as serious efficiency roll-off at a high current density. Here, a multifunction gain material, functioning both as a thermally activated delayed fluorescence (TADF) emitter with exceptional optical gain and as a source of phosphorescence, was theoretically investigated. The new molecule we designed exhibits a reduction of triplet accumulation through an effective exciton radiative process (5-fold boost in figure of merit) and significantly decreased exciton binding energy (dipole moment from 5.77 to 14.03 D), which benefit amplified spontaneous emission and lasing emission. Our work provides theoretical insights into organic solid-state lasers and may contribute to the development of new and efficient laser-gaining molecules.