Porphyrin sensitizers with acceptor structural engineering for dye-sensitized solar cells

Abstract

Two porphyrin-based sensitizers, SGT-028 and SGT-029, were designed and synthesized via acceptor engineering for application in dye-sensitized solar cells (DSSCs). Porphyrin SGT-028 was designed by introducing a salicylic acid anchoring group instead of a conventional benzoic acid in the platform of donor-porphyrin-triple bond-BTD-phenyl-acceptor sensitizers (e.g., SGT-021 and SM315). As for SGT-029, an additional alkylated benzothiadiazole (BTD) unit was substituted to the BTD of D-pi-A porphyrin sensitizers. The impact of the anchoring group and long alkyl chains on the optical character, electrochemical property, and photovoltaic performance were studied and also compared with a reference dye of SGT-021, which had previously been synthesized by our group. As a result, both of these two porphyrin sensitizers obtained a similar absorption range and energy band gap to SGT-021 dye. After performing optimization of DSSC devices, SGT-029 achieved a comparatively high power conversion efficiency (PCE) of 10.5%, but was inferior to the benchmark porphyrin sensitizer SGT-021 (12.7%), and a slightly lower PCE of 9.1% was exhibited by SGT-028, under the standard AM 1.5G light intensity. It is worth mentioning that the PCE of 12.7% is the highest efficiency for a SGT-021-based device up to now. The main reason was supposed to be the dye adsorption amount difference, maybe allowing for a serious dye aggregation, which often leads to an increased quenching of excited states and limits the charge injection into the TiO2 semiconductor substrate, and lower light harvest efficiency (LHE), resulting in lower photocurrent, photovoltage, and PCE.