Novel Organic Light-Emitting Diode with Ultralow Turn-on Voltage for Blue Emission
An upconversion organic light-emitting diode (OLED) based on a typical blue-fluorescence emitter achieves emission at an ultralow turn-on voltage of 1.47 V. Their technology circumvents the traditional high voltage requirement for blue OLEDs, leading to potential advancements in commercial smartphone and large screen displays.
Figure 1. Lighting up a blue organic LED with a single AA battery
Background of the Research
Blue light is vital for light-emitting devices, lighting applications, as well as smartphone screens and large screen displays. However, it is challenging to develop efficient blue organic light-emitting diodes (OLEDs) owing to the high applied voltage required for their function. Conventional blue OLEDs typically require around 4 V for a luminance of 100 cd/m2; this is higher than the industrial target of 3.7 V—the voltage of lithium-ion batteries commonly used in smartphones. Therefore, there is an urgent need to develop novel blue OLEDs that can operate at lower voltages.
In this regard, professors Masahiro Morimoto and Shigeki Naka from University of Toyama, collaborated with researchers from Tokyo Institute of Technology and Osaka University, Shizuoka University, and the Institute for Molecular Science has recently presented a novel OLED device with a remarkable ultralow turn-on voltage of 1.47 V for blue emission and a peak wavelength at 462 nm (2.68 eV) (as shown in Figure 1). Their work has been published in Nature Communications.
Research Content and Achievements
The choice of materials used in this OLED significantly influences its turn-on voltage. The device utilizes NDI-HF (2,7-di(9H-fluoren-2-yl)benzo[lmn][3,8]-phenanthroline-1,3,6,8(2H,7H)-tetraone) as the acceptor, 1,2-ADN (9-(naphthalen-1-yl)-10-(naphthalen-2-yl)anthracene) as the donor, and TbPe (2,5,8,11-tetra-tert-butylperylene) as the fluorescent dopant. This OLED operates via a mechanism called upconversion (UC). Herein, holes and electrons are injected into donor (emitter) and acceptor (electron transport) layers, respectively. They recombine at the donor/acceptor (D/A) interface to form a charge transfer (CT) state. Authors point out: “The intermolecular interactions at the D/A interface play a significant role in CT state formation, with stronger interactions yielding superior results.”
Subsequently, the energy of the CT state is selectively transferred to the low-energy first triplet excited states of the emitter, which results in blue light emission through the formation of a high-energy first singlet excited state by triplet-triplet annihilation (TTA). “As the energy of the CT state is much lower than the emitter’s bandgap energy, the UC mechanism with TTA significantly decreases the applied voltage required for exciting the emitter. As a result, this UC-OLED reaches a luminance of 100 cd/m2, equivalent to that of a commercial display, at just 1.97 V,” explains this article.
In effect, this study efficiently produces a novel OLED, with blue light emission at an ultralow turn-on voltage, using a typical fluorescent emitter widely utilized in commercial displays, thus marking a significant step toward meeting the commercial requirements for blue OLEDs. It emphasizes the importance of optimizing the design of the D/A interface for controlling excitonic processes and holds promise not only for OLEDs but also for organic photovoltaics and other organic electronic devices.
Let us hope that this technology gets commercialized soon.
Seiichiro Izawa1,2,3,*, Masahiro Morimoto4 , Keisuke Fujimoto5, Koki Banno5, Yutaka Majima1, Masaki Takahashi5, Shigeki Naka4, and Masahiro Hiramoto6
1Laboratory for Materials and Structures, Institute of Innovative Research, Tokyo Institute of Technology
2Joining and Welding Research Institute, Osaka University
3Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency (JST)
4Academic Assembly Faculty of Engineering, University of Toyama
5Department of Applied Chemistry, Faculty of Engineering, Shizuoka University
6Institute for Molecular Science
Blue Organic Light-Emitting Diode with a Turn-on Voltage of 1.47 V
Nature Communications, 14, 5494 (2023)