Pyrene-conjugated porphyrins for efficient mesoscopic solar cells: the role of the spacer

Abstract

With a view to broadening the porphyrin light-harvesting cross section and improving mesoporous solar cell power conversion efficiency, pyrene-conjugated porphyrin dyes with various π-spacers between the porphyrin chromophore and carboxylic acid have been designed and synthesized in this study, including tailoring with phenyl (LW17), thiophene (LW18), and 2-phenylthiophene (LW19). These porphyrins show stepwise red-shifted absorption spectra and consistently decreased oxidation potential when the spacer changes from phenyl to an electron-rich unit of thiophene, and to an elongated spacer of 2-phenylthiophene, respectively, for LW17, LW18, and LW19 dyes. A mesoporous solar cell based on LW18 dye can achieve an overall power conversion efficiency of 8.7% under full sunlight (AM 1.5G, 100 mW cm⁻²) irradiation. The result reveals that both photocurrent and photovoltage can be effectively tuned by changing the spacers. Detailed investigation with transient photovoltage decay measurements provides general information on factors affecting the principal photovoltaic parameters.