Browsing by Author "Yao, Ching-Fa"

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Effects of Porphyrinic meso-Substituents on the Photovoltaic Performance of Dye-Sensitized Solar Cells: Number and Position of p-Carboxyphenyl and Thienyl Groups on Zinc Porphyrins
(2012-06-07)
Ambre, Ram
;
Chen, Kwan-Bo
;
Yao, Ching-Fa
;
Luo, Liyang
;
Diau, Eric Wei-Guang
In order to understand the effects of meso-substituents of the zinc porphyrins on optical, electrochemical, and photovoltaic properties, a series of porphyrins with different combinations of thienyl (S) and p-carboxyphenyl (A) groups as the meso substituents have been systematically synthesized and studied. The properties of zinc complexes 3S1A, trans-2S2A, cis-2S2A, and 1S3A were fully investigated by absorption and emission spectra, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectra, density functional theory (DFT) calculations, electrochemical, photophysical, and photovoltaic measurements. With the increasing number of meso-thienyl groups, slight red-shifts of Soret and Q bands were observed in both absorption and emission spectra. All of the absorption spectra of zinc porphyrins on TiO2 film show broadening and splitting of Soret bands because of excitonic coupling of porphyrins. ATR-FTIR spectra revealed likely modes to determine either a single arm (in 3S1A and trans-2S2A) or double arms (in 1S3A and cis-2S2A) attached on TiO2. Two factors of p-carboxyphenyl and thienyl groups affecting the devices performance-heavy atom effect and the amount of dye loading on TiO2-are concluded. Overall, the power conversion efficiencies (eta) of the devices exhibit the following order: 1S3A (3.0%) > cis-2S2A (2.5%) > trans-2S2A (1.8%) >> 3S1A (0.2%).
New Dual Donor-Acceptor (2D--2A) Porphyrin Sensitizers for Stable and Cost-Effective Dye-Sensitized Solar Cells
(2013-09-01)
Ambre, Ram B.
;
Chang, Gao-Fong
;
Zanwar, Manoj R.
;
Yao, Ching-Fa
;
Diau, Eric Wei-Guang
A series of porphyrin sensitizers that featured two electron-donating groups and dual anchoring groups that were connected through a porphine -bridging unit have been synthesized and successfully applied in dye-sensitized solar cells (DSSCs). The presence of electron-donating groups had a significant influence on their spectroscopic, electrochemical, and photovoltaic properties. Overall, the dual anchoring groups gave tunable electronic properties and stronger attachment to TiO2. These new dyes were readily synthesized in a minimum number of steps in gram-scale quantities. Optical and electrochemical data confirmed the advantages of these dyes for use as sensitizers in DSSCs. Porphyrins with electron-donating amino moieties provided improved charge separation and better charge-injection efficiencies for the studied dual-push-pull dyes. Attenuated total reflectance-Fourier-transform infrared (ATR-FTIR) and X-ray photoelectron spectroscopy of the porphyrin dyes on TiO2 suggest that both p-carboxyphenyl groups are attached onto TiO2, thereby resulting in strong attachment. Among these dyes, cis-Zn2BC2A, with two electron-donating 3,6-ditertbutyl-phenyl-carbazole groups and dual-anchoring p-carboxyphenyl groups, showed the highest efficiency of 4.07%, with JSC=9.81mAcm-2, VOC=0.63V, and FF=66%. Our results also indicated a better photostability of the studied dual-anchored sensitizers compared to their mono-anchored analogues under identical conditions. These results provide insight into the developments of a new generation of high-efficiency and thermally stable porphyrin sensitizers.