Two novel donor-π-acceptor (D-π-A type) porphyrin dyes were successfully synthesized and use in a dye-sensitized solar cell (DSSC). The molecular structures of both porphyrins are composed of the same dialkyl-substituted diphenylamino unit acting as the donor part, and two bisalkoxyphenyl substituents at the 5,15-meso positions. The acceptor part is composed of different ethyne-linked π-extended bridges, and a cyanoacrylic acid (Dye I) or carboxyphenyl (Dye II) moiety acting as anchoring groups. In order to investigate the effects of including the π-extended bridge between the porphyrin and acceptor unit, two different π-extended bridges such as 2,2′-bithiophene and 2-(phenylethynyl)-thiophene, were employed. In particular, Dye II contains two triple bonds between donor substituted porphyrin and carboxylic acid group. These modifications could potentially reduce dye aggregation on the TiO2 surface. The charge recombination resistance and diffusion length for the cells with Dye II were relatively higher for all the measured ranges of bias potentials, implying that electron recombination loss from injected electrons was highly suppressed when Dye II molecules were adsorbed on the TiO2 surface. Eventually, Dye II containing a 2,2′-bithiophene π-spacer and anchored trough a carboxyphenyl group exhibited a superior power conversion efficiency of 6.7% under AM 1.5 illumination (100 mW.cm-2) in a photoactive area of 0.46 cm 2 than Dye I with a 2-(phenylethynyl)thiophene (PCE = 3.5%) anchored through a cyanoacrylic group.
Bibliographical noteFunding Information:
This work was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Ministry of Knowledge Economy under contract No. 20103020010010 and by Key Research Institute Program (NRF 20100020209) and KNRF program (NRF 2013007429) through the NRF funded by the Ministry of Education, Science and Technology.
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