Metal-free organic dyes with di(1-benzothieno)[3,2-b:2′,3′-d]pyrrole as a donor for efficient dye-sensitized solar cells: Effect of mono- and bi-anchors on photovoltaic performance

Four novel metal-free organic dyes WL1a-b and WL2a-b containing di(1-benzothieno)[3,2-b:2',3'-d]pyrrole (DBTP) as electron donor were synthesized and applied for dye-sensitized solar cells (DSSCs), where DBTP was firstly employed as a donor in the organic dyes. It has been demonstrated that the dyes WL with DBTP as a donor show better photovoltaic performance than the reference dye PTZ with phenothiazine as a donor. In comparison with WL1a-b with one cyanoacrylic acid as mono-anchor, WL2a-b with two cyanoacrylic acids as bi-anchors show a broader light absorption on the TiO2 film and higher molar extinction coefficients in solution, resulting in higher power conversion efficiency. Under standard global AM 1.5G solar light condition, WL2a sensitized solar cell obtained a high power conversion efficiency of 8%. The results indicate that the DBTP unit can be applied as an effective electron donor and DBTP-based organic dye is a promising candidate for efficient DSSCs.