Browsing by Author "Shiu, Jia-Wei"

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Co-Sensitization of Zinc and Free-Base Porphyrins with an Organic Dye for Efficient Dye-Sensitized Solar Cells
(2014-12-04)
Wang, Chin-Li
;
Shiu, Jia-Wei
;
Hsiao, Yen-Ni
;
Chao, Pei-Shang
;
Diau, Eric Wei-Guang
Co-sensitization of an efficient zinc porphyrin sensitizer (LD14) with its free-base analogue (H(2)LD14) and an organic dye (AN-3) improves the efficiency of the dye-sensitized solar cells. The superior performance of the co-sensitized system is attributed to complementary absorptions of the three dyes, resulting in panchromatic incident photon-to-current conversion efficiency responses at the expense of only slightly lowered open-circuit voltage.
Construction of a photoanode with varied TiO2 nanostructures for a Z907-sensitized solar cell with efficiency exceeding 10%
(2014)
Shiu, Jia-Wei
;
Lan, Zih-Jian
;
Chan, Chien-Yi
;
Wu, Hui-Ping
;
Diau, Eric Wei-Guang
For Z907-based dye-sensitized solar cells, we constructed photoanodes, layer by layer, containing titania nanostructures of varied types - spherical nanoparticles (NPs), one-dimensional nanorods (NRs), and octahedron-like nanocrystals of varied size (HD1-HD3), in either a bi-layer (BL) or a multi-layer (ML) film configuration. To understand the kinetics of electron transport in these devices, we measured charge extraction, intensity-modulated photocurrent spectra and photovoltage spectra of devices made of either these nanomaterials or hybrid HD-NP composites (HDP). The HD devices featured an excellent characteristic of electron transport and upward-shifted potentials to produce V-OC greater than those of the NP and NR devices, but the latter featured a larger dye loading to give J(SC) greater than that for the former; the devices fabricated with hybrid HDP films showed enhanced J(SC) and balanced V-OC to perform better than their individual counterparts. We constructed the ML devices based on the NP-BL system with additional HDP layers inserted between the two components, NP and SL, to enhance J(SC) so as to attain the best performance, with efficiency of power conversion (PCE) = 10.1%, at a film thickness (L) of 26 mu m. Because of the robust structural feature of the HD films, the devices fabricated with a simple BL film configuration, HD1/SL = 6/3, exhibited the best performance, PCE = 10.2% at L = 29 mu m, which is a promising advance for Z907-based solar cells with a superior and enduring stability of performance for commercialization.
Femtosecond Excitonic Relaxation Dynamics of Perovskite on Mesoporous Films of Al2O3 and NiO Nanoparticles
(2014-08-25)
Hsu, Hung-Yu
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Wang, Chi-Yung
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Fathi, Amir
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Shiu, Jia-Wei
;
Chung, Chih-Chun
The excitonic relaxation dynamics of perovskite adsorbed on mesoporous thin films of Al2O3 and NiO upon excitation at 450 nm were investigated with femtosecond optical gating of photoluminescence (PL) via up-conversion. The temporal profiles of emission observed in spectral region 670-810 nm were described satisfactorily with a composite consecutive kinetic model and three transient components representing one hot and two cold excitonic relaxations. All observed relaxation dynamics depend on the emission wavelength, showing a systematic time-amplitude correlation for all three components. When the NiO film was employed, we observed an extent of relaxation proceeding through the non-emissive surface state larger than through the direct electronic relaxation channel, which quenches the PL intensity more effectively than on the Al2O3 film. We conclude that perovskite is an effective hole carrier in a p-type electrode for NiO-based perovskite solar cells showing great performance.
Formation of size-tunable dandelion-like hierarchical rutile titania nanospheres for dye-sensitized solar cells
(2013)
Lan, Chi-Ming
;
Liu, Shang-En
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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.
High-Performance and Stable Gel-State Dye-Sensitized Solar Cells Using Anodic TiO2 Nanotube Arrays and Polymer-Based Gel Electrolytes
(2015-06-17)
Seidalilir, Zahra
;
Malekfar, Rasoul
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Wu, Hui-Ping
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Shiu, Jia-Wei
;
Diau, Eric Wei-Guang
Highly ordered and vertically oriented TiO2 nanotube (NT) arrays were synthesized with potentiostatic anodization of Ti foil and applied to fabricate gel-state dye-sensitized solar cells (DSSCs). The open structure of the TiO2 NT facilitates the infiltration of the gel-state electrolyte; their one-dimensional structural feature provides effective charge transport. TiO2 NTs of length L = 15-35 mu m were produced on anodization for periods of t = 5-15 h at a constant voltage of 60 V, and sensitized with N719 for photovoltaic characterization. A commercially available copolymer, poly(methyl methacrylate-co-ethyl acrylate) (PMMA-EA) served as a gelling agent to prepare a polymer-gel electrolyte (PGE) for DSSC applications. The PGE as prepared exhibited a maximum conductivity of 4.58 mS cm(-1) with PMMA-EA (7 wt %). The phase transition temperature (T-p) of the PGE containing PMMA-EA at varied concentrations was determined on the basis of the viscosities measured at varied temperatures. T-p increased with increasing concentration of PMMA-EA. An NT-DSSC with L = 30 mu m assembled using a PGE containing PMMA-EA (7 wt %) exhibited an overall power conversion efficiency (PCE) of 6.9%, which is comparable with that of a corresponding liquid-type device, PCE = 7.1%. Moreover, the gel-state NT-DSSC exhibited excellent thermal and light-soaking enduring stability: the best device retained similar to 90% of its initial efficiency after 1000 h under 1 sun of illumination at 50 degrees C, whereas its liquid-state counterpart decayed appreciably after light soaking for 500 h.
High-Performance Gel-Type Dye-Sensitized Solar Cells Using Poly (methyl methacrylate-co-ethylacrylate)-Based Polymer Gel Electrolyte with Superior Enduring Stability
(2015-01-01)
Seidalilir, Zahra
;
Malekfar, Rasoul
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Shiu, Jia-Wei
;
Wu, Hui-Ping
;
Diau, Eric Wei-Guang
We fabricated high-performance gel-state dye-sensitized solar cells (DSSCs) using TiO2 nanoparticles (NPs) and one-dimensional TiO2 nanotube (NT) arrays as electrodes and a polymer gel electrolyte (PGE), poly(methyl methacrylate-co-ethyl acrylate) (PMMA-EA), as a gelator in 3-methoxypropionitrile (MPN). MPN instead of acetonitrile (ACN) was used as a solvent to prepare PGE to overcome the drawback of high volatility of ACN so as to improve the long-term stability of the devices. The viscosities of the PGEs containing varied concentrations of PMMA-EA copolymer (4-13 wt%) were measured to obtain the gel to liquid phase transition temperature (T-p) of the PGEs. T-p systematically increased with increasing concentration of PMMA-EA. We found that the as prepared PGE showed the best electrical conductivity of 1.6 mS cm(-1) at 10 wt% of PMMA-EA, which is comparable with the value of the liquid electrolyte (1.7 mS cm(-1)). By employing 10 wt% of PMMA-EA as POE in MPN, the gel-type NT and NP-based devices exhibited power conversion efficiencies (PCE) 6.3 and 8.4%, respectively, which are comparable to those of the corresponding liquid-type counterparts, PCE = 6.4 and 9.1%, respectively. In addition, the enduring stability of MPN-based gel-state device was found to retain a high device efficiency for a long period under thermal and light-soaking dual stress. (C) 2015 The Electrochemical Society. All rights reserved.
Hybrid Titania Photoanodes with a Nanostructured Multi-Layer Configuration for Highly Efficient Dye-Sensitized Solar Cells
(2013-05-02)
Wu, Hui-Ping
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Lan, Chi-Ming
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Hu, Jyun-Yu
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Huang, Wei-Kai
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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.
Morphological control of platinum nanostructures for highly efficient dye-sensitized solar cells
(2012)
Li, Lu-Lin
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Chang, Chia-Wei
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Wu, Hsin-Hui
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Shiu, Jia-Wei
;
Wu, Po-Ting
Cyclic electro-deposition (CED) is a cost-effective tool to synthesize nanostructures with a solution process, controllable morphology and high purity. Here we report novel platinum nanostructures fabricated according to CED at room temperature in solution containing H2PtCl6 precursor and NaNO3. Remarkable Pt nanostructures-from nanoclusters, nanosheets, nanograsses to nanoflowers-were produced through morphological control via variation of either period of CED scans or concentration of the precursor. Pt films with uniform nanograss structures have great electrocatalytic performance (electron-transfer resistance = 0.3 Omega) and intrinsic light-scattering (reflectivity similar to 50%), perfectly suitable for use as counter-electrodes for dye-sensitized solar cells (DSSCs). The DSSC device made with the Pt-nanograss counter-electrode and N719 dye attained efficiency eta = 9.61% of power conversion, which is 12% enhanced from that fabricated according to a conventional thermal decomposition method (eta = 8.55%) under similar experimental conditions. When the devices were further optimized with a thick TiO2 film (17 + 5 mu m) sensitized by Z907 dye using the CED-Pt counter-electrode, we obtained J(SC) (mA cm(-2)) = 19.44, V-OC (V) = 0.742, and FF = 0.736, giving an exceptional power conversion efficiency of 10.62%.
Panchromatic co-sensitization of porphyrin-sensitized solar cells to harvest near-infrared light beyond 900 nm
(2015-01-01)
Shiu, Jia-Wei
;
Chang, Yen-Cheng
;
Chan, Chien-Yi
;
Wu, Hui-Ping
;
Hsu, Hung-Yu
We designed a dimeric porphyrin dye (LDD1) based on an efficient push-pull zinc porphyrin (LD14) with extended pi-conjugation through coupling of two zinc porphine cores via an acetylene bridge at the meso position of the porphyrin to extend the absorption spectrum effectively into the near infrared region. The effect of dye aggregation among porphyrin molecules was significantly suppressed when the LDD1 and LD14 dyes were co-sensitized on a nanocrystalline TiO2 film in a dye-sensitized photovoltaic system. The light-harvesting ability of the device exhibits a panchromatic feature covering a broad spectral region from 400 nmto 900 nm, which results in a short-circuit current density of 21.3 mA cm(-2) and a power conversion efficiency of 10.4% in an iodine-based solar cell.
Size-Controlled Anatase Titania Single Crystals with Octahedron-like Morphology for Dye-Sensitized Solar Cells
(2012-12-01)
Shiu, Jia-Wei
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Lan, Chi-Ming
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Chang, Yu-Cheng
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Wu, Hui-Ping
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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.