Browsing by Author "Yeh, Chen-Yu"

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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 alkoxy-wrapped push-pull porphyrins for dye-sensitized solar cells
(2012)
Ripolles-Sanchis, Teresa
;
Guo, Bo-Cheng
;
Wu, Hui-Ping
;
Pan, Tsung-Yu
;
Lee, Hsuan-Wei
Three alkoxy-wrapped push-pull porphyrins were designed and synthesized for dye-sensitized solar cell (DSSC) applications. Spectral, electrochemical, photovoltaic and electrochemical impedance spectroscopy properties of these porphyrin sensitizers were well investigated to provide evidence for the molecular design.
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 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.
Electroabsorption spectra of push-pull porphyrins in solution and in solid films
(2015-01-01)
Awasthi, Kamlesh
;
Hsu, Hung-Yu
;
Chiang, Hung-Chu
;
Mai, Chi-Lun
;
Yeh, Chen-Yu
Polarized electroabsorption (E-A) spectra of highly efficient porphyrin sensitizers (YD2 and YD2-oC8) have been measured in benzene solution. Polarized E-A spectra of these push-pull porphyrins embedded in poly(methyl methacrylate) films or sensitized on TiO2 films are also observed. Based on the analysis of the E-A spectra, the magnitude of the electric dipole moment both in the ground state and in the lowest excited state have been evaluated in solution and in solid films. The electric dipole moment in the excited state of these compounds is very large on TiO2 films, suggesting the interfacial charge transfer on TiO2 surface following photoexcitation of porphyrin dyes. The electric dipole moment in the excited state evaluated from the E-A spectra is very different from the one evaluated from the electrophotoluminescence spectra on TiO2, suggesting that the strong local field of TiO2 films is applied to the fluorescing dyes attached to TiO2 films.
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.
Enhanced light harvesting in mesoporous TiO(2)/P3HT hybrid solar cells using a porphyrin dye
(2011-01-01)
Moon, Soo-Jin
;
Baranoff, Etienne
;
Zakeeruddin, Shaik M.
;
Yeh, Chen-Yu
;
Diau, Eric Wei-Guang
We report panchromatic light harvesting in hybrid TiO(2)/P3HT photovoltaic devices using a porphyrin dye that complements the light absorption of P3HT. The high short circuit photocurrent (12.1 mA cm(-2)) obtained is found to be due, in part, to Forster resonance energy transfer from the P3HT to the dye.
Enhanced light harvesting in mesoporous TiO2/P3HT hybrid solar cells using a porphyrin dye
(2011-01-01)
Moon, Soo-Jin
;
Baranoff, Etienne
;
Zakeeruddin, Shaik M.
;
Yeh, Chen-Yu
;
Diau, Eric Wei-Guang
We report panchromatic light harvesting in hybrid TiO2/P3HT photovoltaic devices using a porphyrin dye that complements the light absorption of P3HT. The high short circuit photocurrent (12.1 mA cm(-2)) obtained is found to be due, in part, to Forster resonance energy transfer from the P3HT to the dye.
Field-Induced Fluorescence Quenching and Enhancement of Porphyrin Sensitizers on TiO2 Films and in PMMA Films
(2013-11-28)
Hsu, Hung-Yu
;
Chiang, Hung-Chu
;
Hu, Jyun-Yu
;
Awasthi, Kamlesh
;
Mai, Chi-Lun
Three highly efficient porphyrin sensitizers-YD2, YD2-oC8, and YD30, either sensitized on TiO2 films or embedded in PMMA films were investigated using electrophotoluminescence (E-PL) spectra. Under both thin-film conditions, on application of an external electric field we observed the quenching of fluorescence of push-pull porphyrins (YD2 and YD2-oC8) and a slightly enhanced fluorescence of the reference porphyrin without an electron donor group (YD30). A nonfluorescent state with charge separation (CS) is proposed to be involved in both YD2 and YD2-oC8 systems so that the electron injection becomes accelerated in the presence of a strong electric field. In contrast, the retardation of the nonradiative process not involving a CS state was the reason for the field-induced enhancement of fluorescence of YD30. The extent of fluorescence quenching of YD2-oC8 was greater than that of YD2 on TiO2 films, indicating that the ortho-substituted long alkoxyl chains play a key role to accelerate the consecutive electron injection involving the CS state. Our E-PL results indicate that a field-induced variation of fluorescent intensity is related to the efficiency of conversion of solar energy and that further improvement of the performance of devices containing push pull porphyrin dyes is achievable under an applied electric field.
Highly Efficient Mesoscopic Dye-Sensitized Solar Cells Based on Donor-Acceptor-Substituted Porphyrins
(2010)
Bessho, Takeru
;
Zakeeruddin, Shaik M.
;
Yeh, Chen-Yu
;
Diau, Eric Wei-Guang
;
Graetzel, Michael
Influence of Phenylethynylene of Push-Pull Zinc Porphyrins on the Photovoltaic Performance
(2016-02-10)
Chou, Hsien-Hsin
;
Reddy, Kamani Sudhir K.
;
Wu, Hui-Ping
;
Guo, Bo-Cheng
;
Lee, Hsuan-Wei
A series of zinc porphyrin dyes YD22-YD28 were synthesized and used for dye-sensitized solar cells. Dyes YD26-YD28 consist of zinc porphyrin (ZnP) as core unit, arylamine (Am) as electron-donating group, and p-ethynylbenzoic add (EBA) as an electron-withdrawing/-anchoring group. The dyes YD22-YD25 contain additional phenylethynylene group (PE) bridged between Am and ZnP units. The influence of the PE unit on molecular properties as well as photovoltaic performances were investigated via photophysical and electrochemical studies and density functional calculations. With the insertion of PE unit, the dyes YD22-YD25 possess better light-harvesting properties in terms of significantly red-shifted Q-band absorption. The conversion efficiencies for dyes YD22-YD25 are better than those of dyes YD26-YD28 owing to larger J(SC) output. Natural transition orbitals and Mulliken charge analysis were used to analyze the electron injection efficiency for porphyrin dyes upon time-dependent DFT calculations. The results indicated that insertion of additional PE unit is beneficial to higher J(SC) by means of improved light-harvesting property due to broadened and red-shifted absorption.
Molecular engineering of cocktail co-sensitization for efficient panchromatic porphyrin-sensitized solar cells
(2012-12-01)
Wu, Hui-Ping
;
Ou, Zih-Wei
;
Pan, Tsung-Yu
;
Lan, Chi-Ming
;
Huang, Wei-Kai
Co-sensitization of two or more dyes with complementary absorption spectra on a semiconductor film is an effective approach to enhance the performance of a dye-sensitized solar cell (DSSC). Porphyrin sensitizer YD2-oC8 showed outstanding photovoltaic performance co-sensitized with an organic dye to cover the entire visible spectral region, 400-700 nm. To promote the light-harvesting capability beyond 700 nm, a porphyrin dimer (YDD6) was synthesized for a co-sensitized system. We report a systematic approach for engineering of molecular co-sensitization of TiO2 films in a cocktail solution containing YD2-oC8, an organic dye (CD4) and YDD6 in a specific molar ratio to optimize the photovoltaic performance of the device. The resulting device showed panchromatic spectral features in the IPCE action spectrum in the region 400-700 nm attaining efficiencies of 75-80%; the spectrum is extended to the near-IR region attaining 40-45% in 700-800 nm region, giving J(SC)/mA cm(-2) = 19.28, V-OC/mV = 753, FF = 0.719, and eta = 10.4% under standard AM 1.5 G one-sun irradiation. This performance is superior to what is obtained from the individual single-dye devices and the two-dye co-sensitized systems. The shifts of TiO2 potential upon dye uptake and the kinetics of charge recombination were examined through measurements of the charge extraction (CE) and intensity-modulated photovoltage spectroscopy (IMVS), respectively. Five co-sensitized systems were investigated to demonstrate that suppression of dye aggregation of YDD6 in the co-sensitized film is a key factor to further improve the device performance.
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.
Performance Characterization of Dye-Sensitized Photovoltaics under Indoor Lighting
(2017-04-20)
Chen, Chia-Yuan
;
Jian, Zih-Hong
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Huang, Shih-Han
;
Lee, Kun-Mu
;
Kao, Ming-Hsuan
Indoor utilization of emerging photovoltaics is promising; however, efficiency characterization under room lighting is challenging. We report the first round-robin interlaboratory study of performance measurement for dye-sensitized photovoltaics (cells and mini-modules) and one silicon solar cell under a fluorescent dim light. Among 15 research groups, the relative deviation in power conversion efficiency (PCE) of the samples reaches an unprecedented 152%. On the basis of the comprehensive results, the gap between photometry and radiometry measurements and the response of devices to the dim illumination are identified as critical obstacles to the correct PCE. Therefore, we use an illuminometer as a prime standard with a spectroradiometer to quantify the intensity of indoor lighting and adopt the reverse-biased current voltage (I-V) characteristics as an indicator to qualify the I-V sampling time for dye-sensitized photovoltaics. The recommendations can brighten the prospects of emerging photovoltaics for indoor applications.
Porphyrin Dyes with High Injection and Low Recombination for Highly Efficient Mesoscopic Dye-Sensitized Solar Cells
(2011-06-02)
Barea, Eva M.
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Gonzalez-Pedro, Victoria
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Ripolles-Sanchis, Teresa
;
Wu, Hui-Ping
;
Li, Lu-Lin
The photovoltaic performance and charge recombination characteristics of porphyrin-based dye-sensitized solar cell (DSC) devices have been investigated using the impedance spectroscopy (IS) technique. The IS results provide key information related to the device performance for a highly efficient porphyrin dye (YD2), a reference porphyrin dye (YD0), and a commercial ruthenium dye (N719). The DSC devices constructed using YD2 and N719 dyes reach similar internal power conversion efficiencies (7.41% vs 7.54%) due to the higher injection of the YD2 dye that is compromised by a lower photovoltage. In addition, both YD2 and N719 dyes exhibit the same charge-transfer resistance, indicating that the recombination rates of both dyes are very similar. The diarylamino group plays a key role to repel the triiodide ions from the titania surface so that the charge recombination of YD2 is less significant compared with that of YD0.
Porphyrin sensitizers with pi-extended pull units for dye-sensitized solar cells
(2013)
Reddy, Nagannagari Masi
;
Pan, Tsung-Yu
;
Rajan, Yesudoss Christu
;
Guo, Bo-Cheng
;
Lan, Chi-Ming
New pi-extended porphyrin dyes YD26-YD29 with long alkoxyl chains at the ortho positions of the meso-phenyls, and meta di-tert-butylphenyl-substituted porphyrins YD12-CN, and YD13-CN were synthesized for dye-sensitized solar cells, and their optical, electrochemical and photovoltaic properties were investigated and compared with those of YD12 and YD13. The absorption spectra of YD26-YD29 showed a slight red shift of Soret bands and blue shift of Q bands as compared to the meta-substituted porphyrins due to the electron-donating effects of dioctyloxy substituents at the ortho-positions of the meso-phenyl rings. Replacement of the carboxyl with a cyanoacrylic acid as the anchoring group results in significant broadening and red shifts of the absorptions, which is due to the strong electronic coupling between the pull unit and the porphyrin ring facilitated by the C C triple bond. The electrochemical studies and quantum-chemical calculations (DFT) indicated that the ortho alkoxy-substituted sensitizers exhibit lower oxidation potential, i.e. a higher HOMO energy level, and their HOMO-LUMO gaps are comparable to the meta-substituted analogues. The photovoltaic measurements confirmed that the ortho-octyloxy groups in the two meso-phenyls of YD26 and YD27 play a significant role in preventing dye aggregation thereby enhancing the corresponding short-circuit current density and open-circuit voltage. The power conversion efficiency (eta) of YD26 is 8.04%, which is 11% higher than that of YD12, whereas the efficiency of YD27 is 6.03%, which is 135% higher than that of YD13. On the other hand, the poor performance of YD28 and YD29 is due to the floppy structural nature and limited molecular rigidity of the cyanoacrylic acid anchor.
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.
Porphyrin-Sensitized Solar Cells with Cobalt (II/III)-Based Redox Electrolyte Exceed 12 Percent Efficiency
(2011-11-04)
Yella, Aswani
;
Lee, Hsuan-Wei
;
Tsao, Hoi Nok
;
Yi, Chenyi
;
Chandiran, Aravind Kumar
The iodide/triiodide redox shuttle has limited the efficiencies accessible in dye-sensitized solar cells. Here, we report mesoscopic solar cells that incorporate a Co((II/III))tris(bipyridyl)-based redox electrolyte in conjunction with a custom synthesized donor-pi-bridge-acceptor zinc porphyrin dye as sensitizer (designated YD2-o-C8). The specific molecular design of YD2-o-C8 greatly retards the rate of interfacial back electron transfer from the conduction band of the nanocrystalline titanium dioxide film to the oxidized cobalt mediator, which enables attainment of strikingly high photovoltages approaching 1 volt. Because the YD2-o-C8 porphyrin harvests sunlight across the visible spectrum, large photocurrents are generated. Cosensitization of YD2-o-C8 with another organic dye further enhances the performance of the device, leading to a measured power conversion efficiency of 12.3% under simulated air mass 1.5 global sunlight.
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.