Thienoacene-Based Host Material for Near-Infrared OLED with High Efficiency

A wide variety of organic thin-film devices have been investigated, including light-emitting diodes, photodiodes, transistors, memories and so on. One of the advantages of organic thin-film devices is that elements with various functions can be freely and finely arranged on a single substrate by using vapor deposition and/or coating methods. This capacity in device design will contribute to the evolution of electronic devices, lower costs of products and reduce environmental loads in manufacturing. Our particular interest is in the devices with OLEDs and organic photodiode elements on the same substrate, which can be applied to biometric identification, vital sensing, touchless sensors and so on. While OLEDs and organic solar cells for visible light have been well investigated, there still remain potentials in improvement of the near-infrared OLEDs[1][2][3].<br/>We focused on the intermolecular interactions between organic semiconductors to achieve high luminous efficiency at low voltage drive for near-infrared OLED. In this study, we developed a new naphthodithiophene derivative (NDT) which is expected to show moderate intermolecular interactions in the film. NDT was introduced in near-infrared OLEDs as the host material in its emission layer with the near-infrared dopant 1 vol% of Pt(TPBP)[4] that has an emission peak at 770 nm . Compared to the reference of the DMFL-CBP[5] that is reported to form fine amorphous thin films, the near-infrared OLED with NDT showed 1.5 times higher EQE and 1.1 V lower driving voltage at 10 mA/cm2. As a result, the luminous power efficiency became 1.8 times higher, which is very important in terms of the power consumption of electronic devices. In this contribution, we present the synthesis and characterization of NDT, followed by the fabrication and evaluation results of near-infrared OLED elements.<br/>[1] Andrea Zampetti, Alessandro Minotto, and Franco Cacialli, <i>Adv. Funct. Mater.</i> <b>2019</b>, 29, 1807623 [2] Yuxin Xiao, Hailan Wang, Zongliang Xie, Mingyao Shen, Rongjuan Huang, Yuchen Miao, Guanyu Liu, Tao Yu, and Wei Huang, <i>Chem. Sci.</i> <b>2022</b>, 13, 8906–8923 [3] Hae Un Kim, Taehyun Kim, Chanhyuk Kim, Minjun Kim, and Taiho Park, <i>Adv. Funct. Mater.</i> <b>2023</b>, 33, 2208082 [4] Yiru Sun, Carsten Borek, Kenneth Hanson, Peter I. Djurovich, Mark E. Thompson, Jason Brooks, Julie J.Brown, and Stephen R. Forrest, <i>Appl. Phys. Lett.</i><b> 2007</b>, 444, 213503 [5] Yasuyuki Gotou, Yuko Kobashi, Mitsuharu Noto and Masanao Era, <i>Mol. Cryst. Liq. Cryst.</i><b> 2006</b>, 444, 185–190