Near-Ultraviolet Transparent Organic Hole-Transporting Materials Containing Partially Oxygen-Bridged Triphenylamine Skeletons for Efficient Perovskite Solar Cells
Minh Anh Truong, Hayoon Lee, Ai Shimazaki, Ryota Mishima, Masashi Hino, Kenji Yamamoto, Kento Otsuka, Taketo Handa, Yoshihiko Kanemitsu, Richard Murdey, Atsushi Wakamiya
Abstract
Organic semiconducting materials that are optically transparent in the near-ultraviolet (NUV) region from 300 to 400 nm are needed for advanced perovskite devices such as bifacial semitransparent and tandem solar cells. In this study, three organic semiconducting materials, HND-NAr2, HND-DTP, and HND-Cbz, were designed and synthesized by introducing bis(4-methoxyphenyl)amine, dithieno[3,2-b:2′,3′-d]pyrrole, and carbazole, respectively, into the head position of partially oxygen-bridged triphenylamine skeletons. The combination of oxygen-bridged triphenylamine and an electron-donating group at the head position suppresses the π–π* transition, leading to weak absorption in the NUV region. Thin films of the materials can be fabricated by both solution and vacuum-deposition processes, and applied as the hole-transporting material (HTM) in perovskite solar cells (PSCs). The power conversion efficiency (PCE) of conventional devices with these HTMs was 13.7% (HND-Cbz), 15.0% (HND-DTP), and 17.2% (HND-NAr2). When used in bifacial semitransparent PSCs, the incident photon-to-current conversion efficiency (IPCE) at 400 nm was 41% (HND-NAr2), 45% (HND-Cbz), and 46% (HND-DTP), significantly higher than that of a reference using 2,2′,7,7′-tetrakis(N,N-di-p-metoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) as the HTM (14%) as a result of the improved optical transmission through the HTM.