Spirobifluorene-cored small molecules containing four diketopyrrolopyrrole arms for solution-processed organic solar cells

Spirobifluorene-linked three-dimensional small molecules of SF(DPP)₄ and SF(TDPP)₄ containing four diketopyrrolopyrrole arms were designed and synthesized. Both molecules displayed a broad and strong absorption in the region of 300–700 nm with suitable HOMO and LUMO energy levels as well as high charge carrier mobility. Meanwhile, solution-processed organic solar cells with a device structure of ITO/PEDOT:PSS/active layer/Ca/Al was also fabricated to investigate the photovoltaic properties of SF(DPP)₄ and SF(TDPP)₄. In contrast to that of star-shaped TPA(DPP)₃ in solar cells, enhanced photovoltaic performance with an impressive open circuit voltage of 0.95 V and short-circuit current density of 9.12 mA/cm² was achieved, leading to the maximum power conversion efficiency of 3.72 %. Our result here demonstrated that the three-dimensional-type small molecule in a D–A framework is a promising candidate as electron-donor materials for efficient organic solar cells.