Browsing by Author "Lu, Hsueh-Pei"

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Control of Dye Aggregation and Electron Injection for Highly Efficient Porphyrin Sensitizers Adsorbed on Semiconductor Films with Varying Ratios of Coadsorbate
(2009-12-10)
Lu, Hsueh-Pei
;
Tsai, Chen-Yuan
;
Yen, Wei-Nan
;
Hsieh, Chou-Pou
;
Lee, Cheng-Wei
We report the photovoltaic performances and kinetics of femtosecond fluorescence for three zinc-porphyrin sensitizers (YD0-YD2) coadsorbed with chenodeoxycholic acid (CDCA) at three molar ratios on nanocrystalline semiconductor (TiO(2) or Al(2)O(3)) films. The addition of CDCA improved the efficiencies of YD0 and YD1 so that their maximum performance occurred at a dye/CDCA ratio of 1:2, but the presence of CDCA had a negative effect for YD2. Porphyrin aggregation on TiO(2) surfaces not only accelerates the rate of intermolecular energy transfer but also increases the rate of interfacial electron injection, so that the electron injection yields (Phi(inj)) are balanced by these two important factors. As a result, Phi(inj) increased slightly with increasing amount of CDCA for both YD0 and YD1, but decreased for YD2; for this reason, the presence of CDCA failed to improve the photovoltaic performance for YD2, unlike for YD0 and YD1. The cell performances were optimized on TiO(2) films of similar to 10-mu m thickness with a scattering layer of similar to 4-mu m thickness: the efficiencies 4 if power conversion of YD1 and YD2 are slightly smaller than, but near, that of N719, being 6.5% and 6.8%, respectively, compared to 7.3%. Without a scattering layer on the films, the performance of N719 was degraded significantly (6.3%), whereas the efficiencies of YD1 and YD2 decreased only slightly (6.4% and 6.6%), making this series of green sensitizers promising candidates for future light-penetrable photovoltaic applications.
Design and characterization of highly efficient porphyrin sensitizers for green see-through dye-sensitized solar cells
(2009)
Lu, Hsueh-Pei
;
Mai, Chi-Lun
;
Tsia, Chen-Yuan
;
Hsu, Shun-Ju
;
Hsieh, Chou-Pou
YD12 (eta = 6.7%) is a green sensitizer remarkable for its outstanding cell performance beyond that of N719 (eta = 6.1%) with no added scattering layer; the additional scattering layer assists N719 in promoting the efficiency in the red shoulder of the spectrum, but has only a small effect on the improvement of the cell performance for porphyrins.
Design and Characterization of Novel Porphyrins with Oligo(phenylethylnyl) Links of Varied Length for Dye-Sensitized Solar Cells: Synthesis and Optical, Electrochemical, and Photovoltaic Investigation
(2009-01-15)
Lin, Ching-Yao
;
Lo, Chen-Fu
;
Luo, Liyang
;
Lu, Hsueh-Pei
;
Hung, Chen-Shiung
Novel zinc porphyrins with 1-4 pi-conjugated phenylethyinyl (PE) units (labeled PE1-PE4) as a link of controlled length were synthesized for fundamental tests and applications as a dye-serisitized solar cell (DSSC). The UV-visible spectra of the solution samples show clear absorption patterns of the PE groups in a region 300-400 nm, consistent with results calculated with density-functional theory. Cyclic voltammograms of PE1-PE4 in tetrahydrofuran show similar electrochemical potentials for each compound. Ferntosecond fluorescence up-conversion of solution samples and of porphyrin-sensitized TiO(2) films was measured with excitation at 420 or 430 nm and emission at 460, 470, 620, and 680 nm. When these porphyrins were fabricated into DSSC devices, the efficiency of power conversion of these devices decreased systematically with increasing length of the link: 2.5 +/- 0.2% (PE1), 2.0 +/- 0.1% (PE2), 0.78 +/- 0.09% (PE3), 0.25 +/- 0.02% (PE4). This great photovoltaic degradation from PE1 to PE4 is not interpretable according to the rate of electron injection independent of length; other factors, including electron transfer from the semiconductor back to the porphyrin cation or the electrolyte, must be considered to account for the observed dependence of photovoltaic performance on length.
Design and characterization of porphyrin sensitizers with a push-pull framework for highly efficient dye-sensitized solar cells
(2010)
Wu, Sung-Lin
;
Lu, Hsueh-Pei
;
Yu, Han-Ting
;
Chuang, Shu-Han
;
Chiu, Chien-Lan
Novel porphyrin dyes YD14-YD17 with a push-pull framework were synthesized for dye-sensitized solar cells (DSSC); their spectral, electrochemical and photovoltaic properties were investigated. The absorption bands of these porphyrin dyes are broadened and red-shifted upon introduction of electron-donating groups (EDG) to the meso-positions via extension of p-conjugation. Electrochemical tests show that the first oxidation for these porphyrins occurs at a potential greater than that of the I(-)/I(3)(-) redox couple, and attachment of EDGs to the periphery of the porphyrin facilitates electron abstraction. The photovoltaic measurements show that YD14 and YD17 have a power conversion efficiency of similar to 7%. Introduction of EDGs to various meso-positions is demonstrated to be achievable, and porphyrin dyes with appropriate EDGs are promising candidates for highly efficient DSSCs.
Electronically coupled porphyrin-arene dyads for dye-sensitized solar cells
(2011-12-01)
Lee, Cheng-Wei
;
Lu, Hsueh-Pei
;
Reddy, Nagannagari Masi
;
Lee, Hsuan-Wei
;
Diau, Eric Wei-Guang
An acetylene-linked porphyrin-perylene anhydride and an acetylene-linked porphyrin-naphthalic anhydride have been synthesized; the highly conjugated acetylenic bridge in these porpyrins efficiently mediates electronic interaction between the porphyrin and perylene units to extend the pi-conjugation of the porphyrin dye and to cause both broadening and red shifts of both the Soret and Q absorption bands. This condition is a useful feature for efficient dye-sensitized solar cell applications. The optical, electrochemical and photovoltaic properties of the new linked anhydrides show that the HOMO-LUMO gap decreased upon extension of pi-conjugation, indicating a strong electronic coupling between the porphyrin and the perylene or naphthalene unit. (C) 2011 Elsevier Ltd. All rights reserved.
Fabrication and Photovoltaic Characterization of Bio-Sensitized Solar Cells Using Myoglobin-Based Sensitizers
(2009-03-01)
Chang, Chih-Wei
;
Chang, Chin-Hao
;
Lu, Hsueh-Pei
;
Wu, Tung-Kung
;
Diau, Eric Wei-Guang
Myoglobin (Mb), reconstituted zinc protoporphyrin-apornyoglobin (ZnMb), and eosin-modified ZnMb (EoZnMb) were used as photosensitizers to functionalize TiO(2) nanocrystalline films for biosensitized solar-cell (BSSC) applications. For the Mb-sensitized SC, the poor cell performance was due to a reduction Fe(III) -> Fe(II) that produces a photocurrent density of the device smaller than its unsensitized counterpart. The efficiencies of power conversion of both ZnMb and EoZnMb-sensitized SC were enhanced about ten times due to superior charge separation between TiO(2) and the protein, and due to smaller current leakage between TiO(2) and the electrolyte. The cell performances of the BSSC devices are discussed in terms of an equivalent-circuit model.
Highly efficient catalysts for Co(II/III) redox couples in dye-sensitized solar cells
(2012)
Wang, Liang
;
Diau, Eric Wei-Guang
;
Wu, Mingxing
;
Lu, Hsueh-Pei
;
Ma, Tingli
We developed several low-cost catalysts with high catalytic activity, which were used as counter electrodes in dye-sensitized solar cells (DSCs). They showed higher efficiencies than that of Pt. The efficiencies were improved by 18-42% for the DSCs composed of active carbon, niobium dioxide, ordered mesoporous carbon and commercial titanium carbide.
Novel Zinc Porphyrin Sensitizers for Dye-Sensitized Solar Cells: Synthesis and Spectral, Electrochemical, and Photovoltaic Properties
(2009)
Lee, Cheng-Wei
;
Lu, Hsueh-Pei
;
Lan, Chi-Ming
;
Huang, Yi-Lin
;
Liang, You-Ren
Novel meso- or beta-derivatized porphyrins with a carboxyl group have been designed and synthesized for use as sensitizers in dye-sensitized solar cells (DSSCs). The position and nature of a bridge connecting the porphyrin ring and carboxylic acid group show significant influences on the spectral, electrochemical, and photovoltaic properties of these sensitizers. Absorption spectra of porphyrins with a phenylethynyl bridge show that both Soret and Q bands are red-shifted with respect to those of porphyrin 6. This phenomenon is more pronounced for porphyrins 3 and 4, which have a pi-conjugated electron-donating group at the meso position opposite the anchoring group. Upon introduction of an ethynylene group at the meso position, the potential at the first oxidation alters only slightly whereas that for the first reduction is significantly shifted to the positive, thus indicating a decreased HOMO-LUMO gap. Quantum-chemical (DFT) results support the spectroelectrochemical data for a delocalization of charge between the porphyrin ring and the amino group in the first oxidative state of diarylamino-substituted porphyrin 5, which exhibits the best photovoltaic performance among all the porphyrins under investigation. From a comparison of the cell performance based on the same TiO(2) films, the devices made of porphyrin 5 coadsorbed with chenodeoxycholic acid (CDCA) on TiO(2) in ratios [5]/[CD-CA]=1:1 and 1:2 have efficiencies of power conversion similar to that of an N3-based DSSC, which makes this green dye a promising candidate for colorful DSSC applications.
Porphyrin-Perylene Dyes for Dye-Sensitized Solar Cells
(2010-10-01)
Chen, Hong-Yi
;
Lu, Hsueh-Pei
;
Lee, Cheng-Wei
;
Chuang, Shu-Han
;
Diau, Eric Wei-Guang
Two novel porphyrin-perylene dyads 1 and 2 for DSSC applications have been synthesized. The absorption band of the perylene fills up the trough between the Soret and Q bands of the porphyrin, leading to an increase in the absorption efficiency of the dye. The highly conjugated acetylenic bridge mediates strong electronic coupling between the porphyrin and perylene units and results in the extension of it-conjugation of the porphyrin ring. The Soret and Q bands are broadened and red-shifted and the light-harvesting effect is thus improved. We propose that energy transfer occurs from the photoexcited perylene to porphyrin for dyad 1 whereas energy transfer proceeds from the excited porphyrin to perylene for dyad 2. Our studies show that multichromophoric dyes used for DSSC can be designed in a rational manner with predictable photophysical behavior and efficient light-harvesting properties, but the efficiency of the energy transfer process in a consecutive model needs to be controlled for a significant improvement of the cell performance using perylene-porphyrin sensitizers.
Preparation and Photovoltaic Characterization of Free-Base and Metallo Carboxyphenylethynyl Porphyrins for Dye-Sensitized Solar Cells
(2010-10-01)
Lin, Ching-Yao
;
Lo, Chen-Fu
;
Hsieh, Min-Hsu
;
Hsu, Shun-Ju
;
Lu, Hsueh-Pei
Free-base, manganese, iron, cobalt, nickel, copper and zinc 5-(4-carboxy-phenylethyny1)-10,20-biphenylporphines are synthesized to study the impact of central metal ions to the photovoltaic performance of the solar cells.
Synthesis and characterization of diporphyrin sensitizers for dye-sensitized solar cells
(2010)
Mai, Chi-Lun
;
Huang, Wei-Kai
;
Lu, Hsueh-Pei
;
Lee, Cheng-Wei
;
Chiu, Chien-Lan
Novel porphyrin dimers with broad and strong absorption in the visible and/or near IR regions have been synthesized; the meso-meso-linked porphyrin dimer (YDD1) exhibited the best photovoltaic performance with power conversion efficiency 5.2% under AM 1.5G one solar illumination.
Synthesis and characterization of porphyrin sensitizers with various electron-donating substituents for highly efficient dye-sensitized solar cells
(2010)
Hsieh, Chou-Pou
;
Lu, Hsueh-Pei
;
Chiu, Chien-Lan
;
Lee, Cheng-Wei
;
Chuang, Shu-Han
A series of porphyrin dyes with an electron-donating group (EDG) attached at a meso-position (YD1-YD8) have been designed and synthesized for use as sensitizers in dye-sensitized solar cells (DSSC). The nature of the EDG exerts a significant influence on the spectral, electrochemical and photovoltaic properties of these sensitizers. Absorption spectra of porphyrins having an amino group show broadened Soret band and red-shifted Q bands with respect to those of reference porphyrin YD0. This phenomenon is more pronounced for porphyrins YD7 and YD8 that have a pi-conjugated triphenylamine at the meso-position opposite the anchoring group. Upon introduction of an EDG at the meso-position, the potential for the first oxidation alters significantly to the negative whereas that for the first reduction changes inappreciably, indicating a decreased HOMO-LUMO gap. Results of density-functional theory (DFT) calculations support the spectroelectrochemical data for a delocalization of charge between the porphyrin ring and the amino group in the first oxidative state of diarylamino-substituted porphyrins YD1-YD4, which exhibit superior photovoltaic performance among all porphyrins under investigation. With long-chain alkyl groups on the diarylamino substituent, YD2 shows the best cell performance with J(SC) = 13.4 mA cm(-2), V(OC) = 0.71 V, and FF = 0.69, giving an overall efficiency 6.6% of power conversion under simulated one-sun AM1.5 illumination.
The influence of electron injection and charge recombination kinetics on the performance of porphyrin-sensitized solar cells: effects of the 4-tert-butylpyridine additive
(2013)
Chang, Yu-Cheng
;
Wu, Hui-Ping
;
Reddy, Nagannagari Masi
;
Lee, Hsuan-Wei
;
Lu, Hsueh-Pei
The effects of the 4-tert-butylpyridine (TBP) additive in the electrolyte on photovoltaic performance of two push-pull porphyrin sensitizers (YD12 and YD12CN) were examined. Addition of TBP significantly increased the open-circuit voltage (V-OC) for YD12 (from 550 to 729 mV) but it was to a lesser extent for YD12CN (from 544 to 636 mV); adding TBP also had the effect of reducing the short-circuit current density (J(SC)) slightly for YD12 (from 17.65 to 17.19 mA cm(-2)) but it led to a significant reduction for YD12CN (from 16.45 to 9.78 mA cm(-2)). The resulting power conversion efficiencies of the YD12 devices increase from 6.2% to 8.5% whereas those of the YD12CN devices decrease from 5.8% to 4.5%. Based on measurements of temporally resolved photoelectric transients of the devices and femtosecond fluorescence decays of thin-film samples, the poor performance of the YD12CN device in the presence of TBP can be understood as being due to the enhanced charge recombination, decreased electron injection, and a lesser extent of inhibition of the intermolecular energy transfer.
Tuning Spectral and Electrochemical Properties of Porphyrin-Sensitized Solar Cells
(2010-07-15)
Lo, Chen-Fu
;
Hsu, Shun-Ju
;
Wang, Chin-Li
;
Cheng, Yi-Hui
;
Lu, Hsueh-Pei
Phenylethynyl-substituted porphyrin (PEI) sensitizers bearing a nitro, cyano, methoxy, or dimethylamino phenylethynyl substituent were prepared to examine the electron-donating or -withdrawing effects of dyes on the photovoltaic performance of the corresponding dye-sensitized solar cells. The overall efficiencies of power conversion of the devices show a systematic trend Me(2)N-PE1 > MeO-PE1 > CN-PE1 > NO(2)-PE1, for which Me(2)N-PE1 has a device performance about 90% of that of a N719-sensitized solar cell under the same experimental conditions. The superior performance of Me(2)N-PE1 is attributed to the effective electron-donating property of the dye that exhibits broadened and red-shifted spectral features. According to frontier orbitals based on DFT calculations, the electrons are effectively injected from the dye to TiO(2) for Me(2)N-PE1 and MeO-PE1 upon excitation, but that driving force reverses for NO(2)-PE1. Electrochemical tests indicate that both LUMO and HOMO levels show a systematic trend Me(2)N-PE1 > MeO-PE1 > CN-PE1 > NO(2)-PE1, consistent with the trend of variation of the short-circuit currents in this series of sensitizers.