Controlling triplet-triplet upconversion and singlet-triplet annihilation in organic light-emitting diodes for injection lasing

Significant progress has recently been made in the field of organic solid-state lasers. However, achieving lasing action from organic semiconductors under electrical excitation remains challenging due to losses introduced by triplet excitons. Here, we report experimental and theoretical results that confirm a positive contribution of triplet excitons for electrically-driven organic lasing via a bimolecular triplet-triplet upconversion (TTU) mechanism. We study a model fluorescent material, 9-(9-phenylcarbazole-3-yl)-10-(naphthalene-1-yl)anthracene, revealing that TTU can lower the threshold current densities required to achieve lasing under current injection. However, to achieve the best performance, the singlet-triplet annihilation (STA) must be simultaneously minimized. Hence, an experimental strategy to simultaneously obtain high TTU with low STA is demonstrated in host-guest system with coumarin 545T as the guest laser dye. This system has a low amplified spontaneous emission threshold of 1.7 mu J cm(-)(2) under nanosecond optical pumping, and a more than three orders of magnitude improvement in J(50) in organic light-emitting diodes as compared to a reference blend. Losses induced by triplet excitons are a major obstacle for electrically pumped organic lasers. Here, a combination of enhanced triplet-triplet upconversion and suppressed singlet-triplet annihilation is demonstrated as a route towards lasing in organic light emitting diodes.

Automated summary

Significant progress has been made in the field of organic solid-state lasers. The challenge of achieving lasing action from organic semiconductors under electrical excitation due to energy losses introduced by triplet excitons has been addressed in this study. Experimental and theoretical results demonstrate the positive contribution of triplet excitons through a bimolecular triplet-triplet upconversion mechanism. The study also presents an experimental strategy to simultaneously achieve high triplet-triplet upconversion and low singlet-triplet annihilation, resulting in improved performance in organic light-emitting diodes.