DPP containing D–π–A organic dyes toward highly efficient dye-sensitized solar cells

Two diketopyrrolopyrrole (DPP) containing D–π–A organic dyes, named as TEDBn and TEDTh were prepared. Their optical, electrochemical and photophysical properties were investigated and their application in dye-sensitized solar cells (DSCs) was demonstrated. The broaden absorption and low-energy λmax of DPP containing dyes were contributed from DPP bridge and EDOT π-conjugated moiety. Compared to TEDTh, TEDBn has smaller absorption coefficient and higher optical bandgap. Nevertheless the power conversion efficiency (PCE) of TEDBn based DSC is 7.2% which is larger than that of TEDTh based DSC and 90% of N719 based cell. The higher PCE of TEDBn based device originates from both higher open-circuit voltage (VOC) and short-circuit current (JSC). Femtosecond time-resolved photoluminescence data show that the electron injection at TEDBn/TiO2 is more efficient than that at TEDTh/TiO2 interface, resulting in higher JSC (and IPCE) of TEDBn based DSC. Density function theory (DFT) calculations revealed that TEDBn is a linear structure which leads to higher dye loading on TiO2 than TEDTh which featured a bend conformation, better TiO2 surface coverage, resulting in larger VOC. Therefore, the overall efficiency of the cell sensitized by TEDBn is better than that the devices based on TEDTh.