High-Gain Organic Electroluminescent Device

Abstract

Electrically stimulated emission in organic electroluminescent (EL) gain devices requires high-density excitons generated at high current density, which typically leads to low efficiency and severe efficiency roll-off. To date, limited progress has been made in the development of high-gain EL devices driven at high current densities. Here, we develop a high-efficiency blend material system by combining a custom-designed high-gain dopant, DPASP, with a bipolar-transport host material, 2MCz-CNMCz, which enables efficient triplet exciton utilization. The blend films achieve a high photoluminescence quantum yield of 99%, an extremely low amplified spontaneous emission (ASE) threshold of 0.3 μJ cm–2 and a high net gain coefficient of 73.2 cm–1. A p-i-n heterojunction EL device with a multilayered structure is designed, exhibiting effective suppression of singlet–triplet annihilation (STA) under high current density. The EL device achieves an external quantum efficiency exceeding 2.48% at its critical current density J50 of 1 kA cm–2 and a record radiant exitance of 96 W cm–2 at 3.8 kA cm–2. In addition, the optimized multilayer EL device exhibits a low optically pumped ASE threshold of 3.0 μJ cm–2. More importantly, synchronous electro-optical co-pumping measurements reveal that the electrically injected excitons actively participate in stimulated emission within a time window of approximately 7 ns, resulting in a higher total ASE output intensity compared with that obtained under optical pumping alone. This study demonstrates that effective triplet exciton management enables efficient organic EL devices capable of operating at high current densities. Furthermore, electrically injected excitons are shown to participate in stimulated emission that builds upon the optically pumped ASE.