Browsing by Author "Ambre, Ram B."

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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.
The cis-isomer performs better than the trans-isomer in porphyrin-sensitized solar cells: interfacial electron transport and charge recombination investigations
(2015-01-01)
Luo, Liyang
;
Ambre, Ram B.
;
Mane, Sandeep B.
;
Diau, Eric Wei-Guang
;
Hung, Chen-Hsiung
We report characterizations and device performance for dye-sensitized solar cells using cis- and trans-isomers of 2D-pi-2A zinc porphyrins with carboxyphenyl and thienyl groups in their meso-positions. Under identical experimental conditions with similar dye loadings, we observed overall power conversion efficiencies of 2.44% and 0.88% for devices made of cis-2S2A and trans-2S2A, respectively. This uneven performance among cis and trans isomers under the same experimental conditions can be rationalized with detailed investigations via spectroscopic, quantum chemical, and femtosecond fluorescence up-conversion investigations. Density functional theory (DFT) calculations show that a small amount of electron density is localized over carboxyphenyl groups in the LUMO of cis-2S2A, but there is no electron density populated on the carboxyphenyl groups in the LUMO of trans-2S2A. The femtosecond fluorescence decay measurements revealed that the excited-state lifetime of trans-2S2A on Al2O3 is half of that of cis-2S2A on Al2O3. Moreover, the dye-to-TiO2 electron injection time of trans-2S2A is 2.54 ps, which is shorter than that of cis-2S2A/TiO2 (2.95 ps). Electrochemical impedance spectra measured under one sun illumination also revealed that the charge recombination time of cis-2S2A is longer than that of trans-2S2A. This thorough understanding of isomeric effects on the performance of porphyrins will serve as a guideline for the design of future sensitizing dyes for solar cells.