D-pi-A structured porphyrins for efficient dye-sensitized solar cells

In this study, new push-pull alkoxy-wrapped zinc porphyrin dyes with intramolecular donor-pi-acceptor structures have been designed and synthesized for dye-sensitized solar cells (DSCs). The linkers based on thiophene or 2,3-dihydrothieno[3,4-b][1,4] dioxine with cyanoacetic acid can broaden the spectral response of porphyrins into the near-IR region (similar to 850 nm), which is mainly attributed to the cyanoacetic acid group. However, porphyrins with cyanoacrylic acid as an anchoring group lead to a faster charge recombination rate at the dye-sensitized heterojunction interface, which lowers the device photovoltaic performance. By using porphyrins with a rigid pi-linker feature structure that is 5-ethynylthiophene-2-carboxylic acid, highly efficient DSC devices with a power conversion efficiency of 9.5% can be obtained. Spectral, electrochemical, photovoltage transient decay and impedance measurements are performed to reveal the influence of pi-conjugated linkers and anchoring groups upon the optoelectronic features of porphyrin dyes in DSCs.