A Blue Diketopyrrolopyrrole Sensitizer with High Efficiency in Nickel‐Oxide‐based Dye‐Sensitized Solar Cells

Abstract We prepared a series of four new diketopyrrolopyrroles (DPPs)‐based sensitizers that exhibit high‐molar extinction coefficients, extended absorption into the long wavelengths, and well‐suited photoredox properties to act as sensitizers in p‐type dye‐sensitized solar cells (p‐DSSCs). These new DPP dyes, composed of a thienyl DPP core, are substituted on one end either by a thiophene carboxylic (Th) or a 4,4′‐[(phenyl)aza]dibenzoic acid as anchoring group and, on the other extremity, either by a proton or a naphthalene diimide (NDI) moiety. These new dyes were completely characterized by absorption and emission spectroscopy along with electrochemistry and they were modeled by time‐dependent DFT (TD‐DFT) quantum chemical calculations. The photovoltaic study in p‐DSSC with iodine‐based electrolyte reveals that the Th‐DPP‐NDI dye is particularly efficient ( J sc =7.38 mA cm −2 ; V oc =147 mV; FF=0.32; η =0.35 %) and quite active in the low‐energy region of the solar spectrum (above 700 nm), where only a few NiO dyes are effective. To illustrate the potential of DPP dyes in photocathodes, we designed a highly efficient tandem DSSC composed of a TiO 2 photoanode sensitized by the dye D35 and a NiO photocathode sensitized by Th‐DPP‐NDI. This tandem DSSC gives the highest performances ever reported ( J sc =6.73 mA cm −2 ; V oc =910 mV; η =4.1 %) and, importantly, the tandem cell outcompetes with the sub‐cells.