Influence of the Terminal Electron Donor in D–D−π–A Organic Dye-Sensitized Solar Cells: Dithieno[3,2-b:2′,3′-d]pyrrole versus Bis(amine)

With respect to the electron-withdrawing acceptors of D–A−π–A organic dyes, reports on the second electron-donating donors for D–D−π–A organic dyes are very limited. Both of the dyes have attracted significant attention in the field of dye-sensitized solar cells (DSCs). In this work, four new D–D−π–A organic dyes with dithieno­[3,2-b:2′,3′-d]­pyrrole (DTP) or bis­(amine) donor have been designed and synthesized for a investigation of the influence of the terminal electron donor in D–D−π–A organic dye-sensitized solar cells. It is found that DTP is a promising building block as the terminal electron donor when introduced in the dithiophenepyrrole direction, but not just a good bridge, which exhibits several characteristics: (i) efficiently increasing the maximum molar absorption coefficient and extending the absorption bands; (ii) showing stronger charge transfer interaction as compared with the pyrrole direction; (iii) beneficial to photocurrent generation of DSCs employing cobalt electrolytes. DSCs based on M45 with the Co-phen electrolyte exhibit good light-to-electric energy conversion efficiencies as high as 9.02%, with a short circuit current density (J_SC) of 15.3 mA cm^–2, open circuit voltage (V_OC) of 867 mV and fill factor (FF) of 0.68 under AM 1.5 illumination (100 mW cm^–2). The results demonstrate that N,S-heterocycles such as DTP unit could be promising candidates for application in highly efficient DSCs employing cobalt electrolyte.