Near-Ultraviolet Transparent Organic Hole-Transporting Materials Containing Partially Oxygen-Bridged Triphenylamine Skeletons for Efficient Perovskite Solar Cells

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.