Organic light-emitting diodes (OLEDs)1–5, quantum-dot-based LEDs6–10, perovskite-based LEDs11–13 and micro-LEDs14,15 have been championed to fabricate lightweight and flexible units for next-generation displays and active lighting. Although there are already some high-end commercial products based on OLEDs, costs must decrease whilst maintaining high operational efficiencies for the technology to realise wider impact. Here we demonstrate efficient action of radical-based OLEDs16, whose emission originates from a spin doublet, rather than a singlet or triplet exciton. While the emission process is still spin-allowed in these OLEDs, the efficiency limitations imposed by triplet excitons are circumvented for doublets. Using a luminescent radical emitter, we demonstrate an OLED with maximum external quantum efficiency of 27 per cent at a wavelength of 710 nanometres—the highest reported value for deep-red and infrared LEDs. For a standard closed-shell organic semiconductor, holes and electrons occupy the highest occupied and lowest unoccupied molecular orbitals (HOMOs and LUMOs), respectively, and recombine to form singlet or triplet excitons. Radical emitters have a singly occupied molecular orbital (SOMO) in the ground state, giving an overall spin-1/2 doublet. If—as expected on energetic grounds—both electrons and holes occupy this SOMO level, recombination returns the system to the ground state, giving no light emission. However, in our very efficient OLEDs, we achieve selective hole injection into the HOMO and electron injection to the SOMO to form the fluorescent doublet excited state with near-unity internal quantum efficiency.Organic light-emitting devices containing radical emitters can achieve an efficiency of 27 per cent at deep-red and infrared wavelengths based on the excitation of spin doublets, rather than singlet or triplet states.

中文翻译：

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具有双峰发射的高效自由基发光二极管

有机发光二极管 (OLED)1–5、基于量子点的 LED6–10、基于钙钛矿的 LED11–13 和微型 LED14,15 已被倡导为下一代显示器和主动照明制造轻巧且灵活的单元. 虽然已经有一些基于 OLED 的高端商业产品，但成本必须降低，同时保持高运营效率，该技术才能实现更广泛的影响。在这里，我们展示了基于自由基的 OLED 的有效作用，其发射源自自旋双线态，而不是单线态或三线态激子。虽然在这些 OLED 中仍然允许自旋发射过程，但双线态可以避免三线态激子施加的效率限制。使用发光自由基发射器，我们展示了 OLED 在 710 纳米波长下的最大外部量子效率为 27%，这是深红色和红外 LED 的最高报告值。对于标准的闭壳有机半导体，空穴和电子分别占据最高占据和最低未占据分子轨道（HOMO 和 LUMO），并重新结合形成单线态或三线态激子。自由基发射器在基态有一个单占分子轨道 (SOMO)，提供整体自旋 1/2 双峰。如果——正如在高能基础上所预期的那样——电子和空穴都占据了这个 SOMO 能级，那么复合会使系统返回到基态，不发出光。然而，在我们非常高效的 OLED 中，