Suppressing Exciton-Polaron Annihilation in a D-π-A Organic Semiconductor Toward Electrically Pumped Lasing.

Abstract

Electrically pumped organic lasers hold tremendous potential for next-generation optoelectronic applications. However, their realization remains a grand challenge due to detrimental exciton-polaron annihilation, which is one of the most recognized yet unresolved exciton losses in organic semiconductors under electrical excitation. Unbalanced charge carrier mobilities have been identified as the primary cause of polaron-related annihilation processes. In this work, we address this issue by developing a spirofluorene-cored D-π-A compound that features both outstanding optical gain and balanced carrier mobilities. When integrated into an organic light-emitting diode (OLED) architecture, the newly developed material exhibits enhanced device performance and reduced efficiency roll-off, which can be ascribed to the inhibition of polaron accumulation, as evidenced by the time-resolved electroluminescent measurements. More importantly, electrically pumped transient absorption spectroscopy further confirms the suppression of polaron-induced nonradiative losses, which is crucial for maintaining population inversion and achieving optically pumped lasing in the operating OLED. These findings shed light on how chemical modifications can mitigate exciton-polaron annihilation in operating devices, opening a promising avenue toward the realization of electrically pumped organic lasers.