Enhancement of the photovoltaic performance in D3A porphyrin-based DSCs by incorporating an electron withdrawing triazole spacer

Abstract

In this study, we report the preparation of two novel zinc-porphyrin derivatives (ZnP-3DoH-click-CNCOOH and ZnP-3DoH-click-COOH) and two reference compounds (ZnP-3DoH-CNCOOH and ZnP-3DoH-COOH) as sensitizers in dye-sensitized solar cells (DSCs). The photo-physical and electrochemical measurements along with the computational studies suggest that the four synthesized porphyrin derivatives exhibit appropriate light absorption characteristics as well as suitable molecular orbital levels for their use as sensitizers in DSCs. All the modified zinc-porphyrin complexes bear hexyloxy chains at the ortho-positions of their three phenyl rings and contain either a carboxylic or a cyanoacrylic acid as anchoring group. In the zinc-porphyrin derivatives ZnP-3DoH-click-CNCOOH and ZnP-3DoH-click-COOH, a spacer with an electron withdrawing unit was incorporated between the porphyrin ring and each anchoring group. More specifically, the triazole ring was used as a spacer since it is considered to be a highly efficient electron transfer bridge. In addition, the pentafluoro-phenyl ring was selected due to its strong electron withdrawing ability in both final derivatives (ZnP-3DoH-click-CNCOOH and ZnP-3DoH-click-COOH). Following this strategy, fourfold and eightfold increase of the device performance was observed regarding ZnP-3DoH-click-CNCOOH and ZnP-3DoH-click-COOH, respectively, when compared to the efficiencies achieved with the reference compounds (ZnP-3DoH-COOH and ZnP-3DoH-CNCOOH). A more detailed interpretation of the charge dynamics in these devices was carried out using charge extraction (CE) and open-circuit voltage decay (OCVD) measurements.