Browsing by Author "Lan, Chi-Ming"

Now showing 1 - 13 of 13

A strategy to design highly efficient porphyrin sensitizers for dye-sensitized solar cells
(2011)
Chang, Yu-Cheng
;
Wang, Chin-Li
;
Pan, Tsung-Yu
;
Hong, Shang-Hao
;
Lan, Chi-Ming
We designed highly efficient porphyrin sensitizers with two phenyl groups at meso-positions of the macrocycle bearing two ortho-substituted long alkoxyl chains for dye-sensitized solar cells; the ortho-substituted devices exhibit significantly enhanced photovoltaic performances with the best porphyrin, LD14, showing J(SC) = 19.167 mA cm(-2), V(OC) = 0.736 V, FF = 0.711, and overall power conversion efficiency eta = 10.17%.
Enhanced light harvesting with pi-conjugated cyclic aromatic hydrocarbons for porphyrin-sensitized solar cells
(2011-05-01)
Wang, Chin-Li
;
Chang, Yu-Cheng
;
Lan, Chi-Ming
;
Lo, Chen-Fu
;
Diau, Eric Wei-Guang
Zinc porphyrins in a series bearing a phenylethynyl, naphthalenylethynyl, anthracenylethynyl, phenanthrenylethynyl or pyrenylethynyl substituent, denoted LD1, LD2, LD3a, LD3p or LD4, respectively, were prepared as photosensitizers for dye-sensitized solar cells. The overall efficiencies of the corresponding devices show a trend LD4 > LD3p > LD2 > LD3a > LD1. Significantly, LD4 features J(SC)/mA cm(-2) 19.627, V(OC)/V = 0.711, and FF = 0.721, giving an efficiency eta = 10.06% of power conversion. This value is superior to that of a N719-based solar cell fabricated under similar experimental conditions. The remarkable performance of the LD4 cell is rationalized to be due to the broader and more red-shifted spectral feature that makes the IPCE spectrum to cover broadly across the entire visible region, 400-800 nm.
Enhanced photovoltaic performance with co-sensitization of porphyrin and an organic dye in dye-sensitized solar cells
(2012-04-01)
Lan, Chi-Ming
;
Wu, Hui-Ping
;
Pan, Tsung-Yu
;
Chang, Chia-Wei
;
Chao, Wei-Shan
We designed a stepwise approach for co-sensitization of a zinc porphyrin sensitizer (LD12) with a spirally configured organic dye (CD5) for dye-sensitized solar cells. The co-sensitized LD12 + CD5 device showed significantly enhanced V-OC and J(SC) relative to its individual single-dye sensitized devices. Upon optimization, the device made of the LD12 + CD5 system yielded J(SC)/mA cm(-2) = 16.7, V-OC/V = 0.74, FF = 0.73 and eta = 9.0%; this performance is superior to that of either individual device made from LD12 (eta = 7.5%) and CD5 (eta = 5.7%) under the same conditions of fabrication. To understand the effects of the potential shift and charge recombination on the cell performance, we measured charge-extraction (CE) and intensity-modulated photovoltage spectra (IMVS). Upon sensitization with each dye, the TiO2 potentials are similar, but co-sensitization causes the potential to shift down (cathodic shift). Charge recombination was significantly retarded for the co-sensitized system relative to each individual dye-sensitized system, to account for the enhanced V-OC for the former relative to the latter. A test of stability indicates a systematic trend between the LD12 + CD5 and LD12 devices; the performance of the co-sensitized device degraded only similar to 15% and remained stable during the period of 500-1000 h near 295 K.
Enveloping porphyrins for efficient dye-sensitized solar cells
(2012-05-01)
Wang, Chin-Li
;
Lan, Chi-Ming
;
Hong, Shang-Hao
;
Wang, Yi-Fen
;
Pan, Tsung-Yu
A series of porphyrins bearing alkoxyl and/or alkyl chains were prepared to investigate the roles of alkoxyl/alkyl chains in the enhanced photovoltaic performance of the dyes. Based on the experimental results and the molecular simulations, we demonstrated that suitable long alkoxyl chains are capable of wrapping the porphyrin core, thus resulting in decreased dye aggregation, elevated excited states and LUMOs, and improved photovoltaic performance.
Fabrication and Characterization of Anodic Titanium Oxide Nanotube Arrays of Controlled Length for Highly Efficient Dye-Sensitized Solar Cells
(2008-12-04)
Chen, Chien-Chon
;
Chung, Hsien-Wen
;
Chen, Chin-Hsing
;
Lu, Hsuch-Pei
;
Lan, Chi-Ming
The performance of dye-sensitized solar cells (DSSC), made of highly ordered anodic titanium oxide (ATO) nanotube (NT) arrays produced directly on Ti foil, depends on the length of these arrays. We controlled these lengths L from 4 to 41 mu m while varying the concentration (0.1, 0.25, 0.5, and 0.8 wt %) of the electrolyte (NH(4)F) in ethylene glycol in the presence of H(2)O (2 vol %) with anodization for various periods (t = 0.5-8 h). The compact and bundle layers introduced. during anodization were effectively removed upon simple ultrasonic cleaning in deionized water containing submicrometer particles of Al(2)O(3) in a small proportion. The photovoltaic performance of the NT-DSSC devices (NH4F at 0.5 wt %) made of ATO films, as prepared, increased from 3.0% to 5.2% as L was increased from 6 mu m (t = 0.5 h) to 30 mu m (t = 8 h). After treatment of the ATO films with TiCl(4) in a two-step annealing process, the optimized NT-DSSC device attained an overall efficiency of 7.0% power conversion.
Formation of size-tunable dandelion-like hierarchical rutile titania nanospheres for dye-sensitized solar cells
(2013)
Lan, Chi-Ming
;
Liu, Shang-En
;
Shiu, Jia-Wei
;
Hu, Jyun-Yu
;
Lin, Meng-Hung
A sol-gel method with a modified solvent comprising of three simple steps under low-temperature conditions was used to synthesize mono-disperse rutile TiO2 nanospheres with dandelion-like hierarchical morphology (DHRS) as a light-scattering layer for dye-sensitized solar cells (DSSC). 1,2-Ethanediol (ED) served as a key retardation agent in the second step at 25 degrees C to slow the hydrolysis and condensation of the TiCl4 aqueous solution prepared in the first step at 0 degrees C; the subsequent nucleation of a rutile type phase occurred homogeneously in the third step at 70 degrees C to generate the rutile TiO2 nanospheres with highly uniform sizes. The spherical sizes of DHRS were well controlled with the volume ratios of the ED-water solvent mixture in the second step, for which the DHRS of diameter 650-200 nm were produced from the solvent system containing 5-25% ED. A detailed mechanism is presented to rationalize the formation of nanospheres of uniform size in six steps: 1) hydration and hydrolysis, 2) hydrolysis and retardation, 3) hydrolysis and condensation, 4) homogeneous nucleation, 5) aggregation and growth of rod-like crystals and 6) DHRS formation. The DSSC device with a scattering layer made of DHRS (size similar to 300 nm) performed comparably to that with a scattering layer made of a commercially available TiO2 paste, making this nano-material a cost-effective alternative for future DSSC commercialization.
Hybrid Titania Photoanodes with a Nanostructured Multi-Layer Configuration for Highly Efficient Dye-Sensitized Solar Cells
(2013-05-02)
Wu, Hui-Ping
;
Lan, Chi-Ming
;
Hu, Jyun-Yu
;
Huang, Wei-Kai
;
Shiu, Jia-Wei
To construct a hybrid titania photoanode containing nanoparticles and nanorods of varied size in a multilayer (ML) configuration for dye-sensitized solar cells, the essence of our ML design is a bilayer system with additional layers of nanorods of well-controlled size inserted between the transparent and the scattering layers to enhance the light harvesting capability for photosensitizers with small absorptivity, such as Z907. We measured charge-extraction and intensity-modulated photoelectric spectra to show the advantages of one-dimensional nanorods with an improved electron-transport property and an upward shift of the potential band edge; a favorable ML configuration was constructed to have a cascade potential feature for feasible electron transport from long nanorods, to normal nanorods, to small nanoparticles. On the basis of the ML system reported herein, we demonstrate how the performance of a Z907 device is improved to attain eta similar to 10%, which is a milestone for its future commercialization.
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.
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.
Size-Controlled Anatase Titania Single Crystals with Octahedron-like Morphology for Dye-Sensitized Solar Cells
(2012-12-01)
Shiu, Jia-Wei
;
Lan, Chi-Ming
;
Chang, Yu-Cheng
;
Wu, Hui-Ping
;
Huang, Wei-Kai
A simple hydrothermal method with titanium tetra-isopropoxide (TTIP) as a precursor and triethanolamine (TEOA) as a chelating agent enabled growth in the presence of a base (diethylamine, DEA) of anatase titania nanocrystals (HD1-HD5) of controlled size. DEA played a key role to expedite this growth, for which a biphasic crystal growth mechanism is proposed. The produced single crystals of titania show octahedron-like morphology with sizes in a broad range of 30-400 nm; a typical, extra large, octahedral single crystal (HD5) of length 410 nm and width 260 nm was obtained after repeating a sequential hydrothermal treatment using 1103 and then 1104 as a seed crystal. The nanocrystals of size similar to 30 nm (HD1) and similar to 300 nm (HD5) served as active layer and scattering layer, respectively, to fabricate N719-sensitized solar cells. These HD devices showed greater V-oc than devices of conventional nanoparticle (NP) type; the overall device performance of HD attained an efficiency of 10.2% power conversion at a total film thickness of 28 mu m, which is superior to that of a NP-based reference device (eta = 9.6%) optimized at a total film thickness of 18-20 mu m. According to results obtained from transient photoelectric and charge extraction measurements, this superior performance of HD devices relative to their NP counterparts is due to the more rapid electron transport and greater TiO2 potential.
Spirally configured cis-stilbene/fluorene hybrids as bipolar, organic sensitizers for solar cell applications
(2012)
Chao, Wei-Shan
;
Liao, Ken-Hsien
;
Chen, Chien-Tien
;
Huang, Wei-Kai
;
Lan, Chi-Ming
Hybrids based on a dibenzosuberene core bearing a spiro-fluorene junction at the C-5 position and with amino donor and beta-thiophenyl-alpha-cyanoacrylic acid acceptor groups at C-3 and C-7, respectively, serve as new organic sensitizer materials for solar cell applications. Solar cell devices based on these materials show a conversion efficiency (eta) of up to 6.1% (V-oc = 697 mV, J(sc) = 12.2 mA cm(-2), FF = 0.72) under AM 1.5 G conditions. The best IPCE values exceed 75% within the 450-550 nm absorption range.
Synthesis and Characterization of Novel Heteroleptic Ruthenium Complexes for Dye-Sensitized Solar Cells
(2010-10-01)
Huang, Wei-Kai
;
Lan, Chi-Ming
;
Liu, Yu-Sin
;
Lee, Pei-Heng
;
Chang, Shu-Mei
We report three novel heteroleptic ruthenium complexes, RD1: Ru[(dcbpy)(1-methyl-2-(pyridin2-yl)-1 H-benzimidazole)(NCS)(2), RD2: Ru [(dcbpy) (2-(pyridine-2-yl) benzothiazole) (NCS)(2), and RD3: Ru[(dcbpy)(2-(pyridin-2-yl) benzoxazole) (NCS)2, for dye-sensitized solar cell applications. We found that RD1 exhibits a dye loading amount two times higher than that of N719, which gives a broad IPCE action spectrum for the spectral response beyond 800 nm. This series of dyes can be easily synthesized in three steps with the best dye (RD1) reaching 80% cell performance of N719.