N-Annulated Perylene as a Coplanar π-Linker Alternative to Benzene as a Low Energy-Gap, Metal-Free Dye in Sensitized Solar Cells

Perylenes are well-known pigments with excellent chemical, thermal, and photochemical stabilities and have been used in various optical and electronic fields. Although for sensitized mesoscopic solar cells there is rapid progress of metal-free thiophene dyes, which now reach over 11.5% power conversion efficiency (PCE) at air mass 1.5 global (AM1.5G) conditions, the so far reported highest PCE of a perylene dye is only 6.8%. Here, a new metal-free organic donor-acceptor (D-A) dye (C261) featuring a bisarylamino functionalized N-annulated perylene electron-releasing segment and a cyanoacrylic acid electron-withdrawing unit is synthesized. Combining a mesoporous titania film grafted by this structurally simple perylene dye with a non-corrosive cobalt redox shuttle, an 8.8% PCE is achieved at an irradiance of the AM1.5G sunlight. By selecting the model dye G221 as a reference, theoretical calculations, steady-state and time-resolved spectroscopies, and electrical measurements are used to compare the energy-levels, light absorptions, and mutichannel charge transfer dynamics that contribute to the photovoltaic behavior.