Unravelling the Spatiotemporal Exciton Dynamics in Electrically Pumped Organic Laser Diodes

Abstract

Organic materials offer wide-band emission covering regions of the spectrum unachievable by conventional semiconductors. If electrically pumped lasing could be demonstrated using these materials, many new classes of optical sensors and detectors could be realized leaving a profound impact on society. Devices fabricated from conducting molecules and polymers have already been demonstrated with polaron densities higher than those which theoretically lead to lasing action; however, threshold remains elusive. Herein, a polymer micro-OLED is reported that achieves record room-temperature current densities of 1.5 (Formula presented.), however despite this, it is not high enough to reach lasing threshold. Using a combination of nanosecond spectrographic techniques and detailed simulation, the mechanisms inhibiting lasing action is unraveled. It is shown that although as previously thought singlet-triplet annihilation is important in pushing threshold higher, photon absorption by excited triplets is as (if not more) important in inhibiting lasing action. The complex dynamics of singlets, triplets, and free/excited polarons in these disordered materials are visualized; establishing a pathway to overcome these bottlenecks and realise electrically pumped organic lasing action. © 2025 Elsevier B.V., All rights reserved.