Porphyrin sensitizers involving a fluorine-substituted benzothiadiazole as auxiliary acceptor and thiophene as π bridge for use in dye-sensitized solar cells (DSSCs)

Three 'donor-acceptor-pi bridge-acceptor' (D-A-pi-A) type zinc porphyrin sensitizers TH-0F, TH-1F and TH-2F with a benzothiadiazole (BTD) unit bearing no fluorine, one fluorine and two fluorine atoms, respectively, as the auxiliary acceptor and thiophene as the pi bridge were designed and synthesized for use in dye-sensitized solar cells (DSSCs). The influence of fluorine atom and thiophene unit on the photophysical and photochemical properties of the sensitizers was investigated. It was shown that the photon to current conversion efficiencies (PCE) of three sensitizer-based devices increased in the order of TH-2F > TH-1F > TH-0F, with the highest PCE of 6.98% achieved for the TH-2F-based device. To further understand the molecular structure of the TH series of dyes, a density functional (DFT) calculation was performed. The result suggests that the strong electron-withdrawing ability of the fluorine atom, along with the intramolecular interaction between the auxiliary acceptor and thiophene, optimized the electronic configuration, thereby facilitating the intramolecular charge transfer efficiency and ultimately improving the performance of the corresponding device.