Browsing by Author "Li, Lu-Lin"

Now showing 1 - 13 of 13

Characterisation of electron transport and charge recombination using temporally resolved and frequency-domain techniques for dye-sensitised solar cells
(2012)
Li, Lu-Lin
;
Chang, Yu-Cheng
;
Wu, Hui-Ping
;
Diau, Eric Wei-Guang
;
應用化學系
We review systematically the kinetic characterisation of electron transport and charge recombination in dye-sensitised solar cells (DSSC) using both temporally resolved and frequency-domain techniques. For the temporally resolved approach, charge extraction (CE), transient-photocurrent decay (TCD) and transient-photovoltage decay (TVD) methods are introduced in detail; for the frequency-domain approach, techniques involving electrochemical impedance spectroscopy (EIS), intensity-modulated photocurrent spectroscopy (IMPS) and intensity-modulated photovoltage spectroscopy (IMVS) are presented in detail. The TCD and TVD data are obtained under short-circuit and open-circuit conditions, respectively, and the electron diffusion coefficients and electron lifetimes are extracted from fitting the decay curves accordingly; the IMPS/IMVS results are the counterparts of the TCD/TVD results in the frequency domain. Even though the EIS results are readily acquired, an accurate interpretation of the data requires an appropriate model to determine the internal features of the device. This review provides an account of each technique about its operating principle, experimental setup and data analysis. As case studies for each technique, examples are given to rationalise the observed potential shift, decay coefficients of electron transport and of charge recombination in relation to the corresponding photovoltaic performance of the device.
Detachment and transfer of ordered TiO(2) nanotube arrays for front-illuminated dye-sensitized solar cells
(2011-09-01)
Li, Lu-Lin
;
Chen, Yi-Ju
;
Wu, Hui-Ping
;
Wang, Niann S.
;
Diau, Eric Wei-Guang
We report a method of detachment and transfer of one-dimensional TiO(2) nanotube (NT) arrays to fabricate dye-sensitized solar cells (DSSCs) with illumination from the front side. The ordered NT arrays (tube length 20 mm) were detached from the NT-Ti substrate, as annealed, by means of a second anodization at 20 V for 4 h and then transferred, inverted, onto a transparent substrate of conducting oxide (TCO) with an interface of TiO(2) nanoparticles of thickness similar to 2 mu m. Dry etching of the NT surface in a highly dense plasma reactor under BCl(3)/Cl(2) for 90 s opened previously closed ends of the tubes. The inverted (bottom-up) NT-TCO substrate was fabricated into a DSSC device that shows a cell performance (eta = 6.24%) significantly improved over those of a front-illuminated counterpart with an upright (face-up) structure (eta = 4.84%) and of a conventional back-illuminated device (eta = 4.61%). Electrochemical impedance spectra (EIS) of the devices under one-sun irradiation were measured to rationalize the cell performances that are consistent with the corresponding interfacial impedances between the NT arrays and the electrode for collection of electrons.
Detachment and transfer of ordered TiO2 nanotube arrays for front-illuminated dye-sensitized solar cells
(2011-09-01)
Li, Lu-Lin
;
Chen, Yi-Ju
;
Wu, Hui-Ping
;
Wang, Niann S.
;
Diau, Eric Wei-Guang
We report a method of detachment and transfer of one-dimensional TiO2 nanotube (NT) arrays to fabricate dye-sensitized solar cells (DSSCs) with illumination from the front side. The ordered NT arrays (tube length 20 mm) were detached from the NT-Ti substrate, as annealed, by means of a second anodization at 20 V for 4 h and then transferred, inverted, onto a transparent substrate of conducting oxide (TCO) with an interface of TiO2 nanoparticles of thickness similar to 2 mu m. Dry etching of the NT surface in a highly dense plasma reactor under BCl3/Cl-2 for 90 s opened previously closed ends of the tubes. The inverted (bottom-up) NT-TCO substrate was fabricated into a DSSC device that shows a cell performance (eta = 6.24%) significantly improved over those of a front-illuminated counterpart with an upright (face-up) structure (eta = 4.84%) and of a conventional back-illuminated device (eta = 4.61%). Electrochemical impedance spectra (EIS) of the devices under one-sun irradiation were measured to rationalize the cell performances that are consistent with the corresponding interfacial impedances between the NT arrays and the electrode for collection of electrons.
Effects of aggregation and electron injection on photovoltaic performance of porphyrin-based solar cells with oligo(phenylethynyl) links inside TiO(2) and Al(2)O(3) nanotube arrays
(2010-01-01)
Luo, Liyang
;
Lin, Chia-Jung
;
Tsai, Chiau-Yiag
;
Wu, Hui-Ping
;
Li, Lu-Lin
Porphyrins with phenylethynyl links of varied length (PE1-PE4) were sensitized on vertically oriented, anodic titanium-oxide (ATO) nanotube arrays for application as dye-sensitized solar cells (DSSC). The efficiency of power conversion decreased systematically from the dye with a short link to the dye with a long link. We measured the efficiency of conversion of incident photons to current (IPCE), the photocurrent decay of the devices, and steady-state and time-resolved fluorescence spectra of the thin-film samples to understand how the cell performance depends on the length of the link. Measurements of femtosecond fluorescence confirmed that the efficiency of electron injection depended on length because of dye aggregation that significantly increased the rate of aggregate-induced energy transfer for porphyrins with a long link. The rate of electron injection depended on the length of the link with an attenuation factor beta similar to 0.1 angstrom(-1). Resonant energy transfer (RET) kinetics of porphyrins sensitized on anodic aluminium-oxide (AAO) nanotube arrays were performed with picosecond time-correlated single-photon counting and four molecular densities for each porphyrin. The kinetic data of PE1 and PE2 are described satisfactorily according to a Forster model, whereas those of PE3 and PE4 conform to a Dexter formula. A formation of clusters is proposed to rationalize the observed density-dependent kinetics for the RET of porphyrins on semiconductor films.
Effects of aggregation and electron injection on photovoltaic performance of porphyrin-based solar cells with oligo(phenylethynyl) links inside TiO2 and Al2O3 nanotube arrays
(2010-01-01)
Luo, Liyang
;
Lin, Chia-Jung
;
Tsai, Chiau-Yiag
;
Wu, Hui-Ping
;
Li, Lu-Lin
Porphyrins with phenylethynyl links of varied length (PE1-PE4) were sensitized on vertically oriented, anodic titanium-oxide (ATO) nanotube arrays for application as dye-sensitized solar cells (DSSC). The efficiency of power conversion decreased systematically from the dye with a short link to the dye with a long link. We measured the efficiency of conversion of incident photons to current (IPCE), the photocurrent decay of the devices, and steady-state and time-resolved fluorescence spectra of the thin-film samples to understand how the cell performance depends on the length of the link. Measurements of femtosecond fluorescence confirmed that the efficiency of electron injection depended on length because of dye aggregation that significantly increased the rate of aggregate-induced energy transfer for porphyrins with a long link. The rate of electron injection depended on the length of the link with an attenuation factor beta similar to 0.1 angstrom(-1). Resonant energy transfer (RET) kinetics of porphyrins sensitized on anodic aluminium-oxide (AAO) nanotube arrays were performed with picosecond time-correlated single-photon counting and four molecular densities for each porphyrin. The kinetic data of PE1 and PE2 are described satisfactorily according to a Forster model, whereas those of PE3 and PE4 conform to a Dexter formula. A formation of clusters is proposed to rationalize the observed density-dependent kinetics for the RET of porphyrins on semiconductor films.
Fabrication of long TiO(2) nanotube arrays in a short time using a hybrid anodic method for highly efficient dye-sensitized solar cells
(2010-01-01)
Li, Lu-Lin
;
Tsai, Chiau-Yiag
;
Wu, Hui-Ping
;
Chen, Chien-Chon
;
Diau, Eric Wei-Guang
We report a simple hybrid anodic method, with initial potentiostatic anodization followed by galvanostatic anodization, to grow much longer titania nanotube ( TNT) arrays in a much shorter anodization period (t). The length of the TNT arrays ( L) depends linearly on t and is controlled by the electric current; the growth rates are 5.3, 10.7 and 20.3 mu m h(-1) for current densities 3.7, 5.6 and 7.5 mA cm(-2), respectively. The produced TNT films of L = 15-57 mu m sensitized with N719 dye were fabricated into devices for photovoltaic characterization. The NT-DSSC devices show systematically improved cell performance depending on L, reflecting the excellent intrinsic light-scattering property of the NT-DSSC devices to harvest increased sunlight with long TNT arrays. The great effective surface area inside TNT arrays has been shown to significantly increase the dye loading, which might help to enhance the cell performance of the device with co-sensitizing of different dyes for improved efficiency of light harvesting in the future. The best performance of the NT-DSSC device was achieved at L similar to 30 mm with a spacer of similar thickness, giving J(SC) = 14.63 mA cm(-2), V(OC) = 0.741 V, FF = 0.70, and eta = 7.6%, which is unprecedented for a back-illumination DSSC.
Fabrication of long TiO2 nanotube arrays in a short time using a hybrid anodic method for highly efficient dye-sensitized solar cells
(2010-01-01)
Li, Lu-Lin
;
Tsai, Chiau-Yiag
;
Wu, Hui-Ping
;
Chen, Chien-Chon
;
Diau, Eric Wei-Guang
We report a simple hybrid anodic method, with initial potentiostatic anodization followed by galvanostatic anodization, to grow much longer titania nanotube ( TNT) arrays in a much shorter anodization period (t). The length of the TNT arrays ( L) depends linearly on t and is controlled by the electric current; the growth rates are 5.3, 10.7 and 20.3 mu m h(-1) for current densities 3.7, 5.6 and 7.5 mA cm(-2), respectively. The produced TNT films of L = 15-57 mu m sensitized with N719 dye were fabricated into devices for photovoltaic characterization. The NT-DSSC devices show systematically improved cell performance depending on L, reflecting the excellent intrinsic light-scattering property of the NT-DSSC devices to harvest increased sunlight with long TNT arrays. The great effective surface area inside TNT arrays has been shown to significantly increase the dye loading, which might help to enhance the cell performance of the device with co-sensitizing of different dyes for improved efficiency of light harvesting in the future. The best performance of the NT-DSSC device was achieved at L similar to 30 mm with a spacer of similar thickness, giving J(SC) = 14.63 mA cm(-2), V-OC = 0.741 V, FF = 0.70, and eta = 7.6%, which is unprecedented for a back-illumination DSSC.
High-Performance Large-Scale Flexible Dye-Sensitized Solar Cells Based on Anodic TiO2 Nanotube Arrays
(2013-10-01)
Jen, Hsiu-Ping
;
Lin, Meng-Hung
;
Li, Lu-Lin
;
Wu, Hui-Ping
;
Huang, Wei-Kai
A simple strategy to fabricate flexible dye-sensitized solar cells involves the use of photoanodes based on TiO2 nanotube (TNT) arrays with rear illumination. The TNT films (tube length similar to 35 mu m) were produced via anodization, and sensitized with N719 dye for photovoltaic characterization. Pt counter electrodes of two types were used: a conventional FTO/glass substrate for a device of rigid type and an ITO/PEN substrate for a device of flexible type. These DSSC devices were fabricated into either a single-cell structure (active area 3.6 X 0.5 cm(2)) or a parallel module containing three single cells (total active area 5.4 cm(2)). The flexible devices exhibit remarkable performance with efficiencies eta = 5.40 % (single cell) and 4.77 % (parallel module) of power conversion, which outperformed their rigid counterparts with eta = 4.87 % (single cell) and 4.50 % (parallel model) under standard one-sun irradiation. The flexible device had a greater efficiency of conversion of incident photons to current and a broader spectral range than the rigid device; a thinner electrolyte layer for the flexible device than for the rigid device is a key factor to improve the light-harvesting ability for the TNT-DSSC device with rear illumination. Measurements of electrochemical impedance spectra show excellent catalytic activity and superior diffusion characteristics for the flexible device. This technique thus provides a new option to construct flexible photovoltaic devices with large-scale, light-weight, and cost-effective advantages for imminent applications in consumer electronics.
Morphologic Characterization of Anodic Titania Nanotube Arrays for Dye-Sensitized Solar Cells
(2010-10-01)
Li, Lu-Lin
;
Tsai, Chiau-Yiag
;
Wu, Hui-Ping
;
Chen, Chien-Chon
;
Diau, Eric Wei-Guang
We report morphologic characterization of the anodic titanium oxide (ATO) films with highly-ordered titania (TiO(2)) nanotube (NT) arrays grown perpendicularly to a titanium (Ti) foil. The length of the ATO arrays was controlled by various electrolytes and anodic periods at a constant applied voltage. In order to enhance the pathways for electron percolation, the ATO film was annealed in an air furnace, forming anatase TiO(2). After TiCl(4) post-treatment to enhance the ruthenium-based dye loading on the ATO surface, the optimized ATO arrays were used as a photoanode in a dye-sensitized solar cell (DSSC). The best performance of the NT-DSSC device was achieved with a NH(4)F-based ATO film at length of 15 pm, giving J(sc) = 12.15 mA cm(-2), V(oc) = 0.74 V, FF = 0.69, and eta = 6.2% under backside illumination.
Morphological control of platinum nanostructures for highly efficient dye-sensitized solar cells
(2012)
Li, Lu-Lin
;
Chang, Chia-Wei
;
Wu, Hsin-Hui
;
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%.
Nanofabrication of uniform and stabilizer-free self-assembled platinum monolayers as counter electrodes for dye-sensitized solar cells
(2014-08-01)
Li, Lu-Lin
;
Wu, Hsin-Hui
;
Tsai, Chia-Hung
;
Diau, Eric Wei-Guang
;
交大名義發表
We report a two-step dip-coating approach for the fabrication of self-assembled monolayers of platinum nanocrystals (SAM-Pt) with a particle size of similar to 3 nm and that are uniformly deposited on a transparent conducting oxide (TCO) surface to serve as a counter electrode (CE) for dye-sensitized solar cells (DSSCs). In the first step, we prepared a polyol solution containing H2PtCl6 and ethylene glycol at 110 degrees C, in which the reduction kinetics were controlled by adding various proportions of NaOH. In the second step, we immersed a thiol-modified TCO substrate into the polyol solution with monodispersed Pt nanoparticles prepared at pH 3.7 at approximately 295 K to complete the nanofabrication. The DSSC devices using Z907 dye as a photosensitizer and the CE prepared using this SAM-Pt approach attained notable photovoltaic performance (eta = 9.2%) comparable with those fabricated using a conventional thermal decomposition method (eta = 9.1%) or a cyclic electrodeposition method (eta = 9.3%) under the same experimental conditions. We emphasize that the SAM-Pt films feature a clean surface, uniform morphology, narrow size distribution, small Pt loading and great catalytic activity; the present approach is hence not only suitable for DSSCs but also applicable for many other energy-related applications that require platinum as an efficient catalyst.
Porphyrin Dyes with High Injection and Low Recombination for Highly Efficient Mesoscopic Dye-Sensitized Solar Cells
(2011-06-02)
Barea, Eva M.
;
Gonzalez-Pedro, Victoria
;
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-sensitized solar cells
(2013)
Li, Lu-Lin
;
Diau, Eric Wei-Guang
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
Nature has chosen chlorophylls in plants as antennae to harvest light for the conversion of solar energy in complicated photosynthetic processes. Inspired by natural photosynthesis, scientists utilized artificial chlorophylls - the porphyrins - as efficient centres to harvest light for solar cells sensitized with a porphyrin (PSSC). After the first example appeared in 1993 of a porphyrin of type copper chlorophyll as a photosensitizer for PSSC that achieved a power conversion efficiency of 2.6%, no significant advance of PSSC was reported until 2005; beta-linked zinc porphyrins were then reported to show promising device performances with a benchmark efficiency of 7.1% reported in 2007. Meso-linked zinc porphyrin sensitizers in the first series with a push-pull framework appeared in 2009; the best cell performed comparably to that of a N3-based device, and a benchmark 11% was reported for a porphyrin sensitizer of this type in 2010. With a structural design involving long alkoxyl chains to envelop the porphyrin core to suppress the dye aggregation for a push-pull zinc porphyrin, the PSSC achieved a record 12.3% in 2011 with co-sensitization of an organic dye and a cobalt-based electrolyte. The best PSSC system exhibited a panchromatic feature for light harvesting covering the visible spectral region to 700 nm, giving opportunities to many other porphyrins, such as fused and dimeric porphyrins, with near-infrared absorption spectral features, together with the approach of molecular co-sensitization, to enhance the device performance of PSSC. According to this historical trend for the development of prospective porphyrin sensitizers used in PSSC, we review systematically the progress of porphyrins of varied kinds, and their derivatives, applied in PSSC with a focus on reports during 2007-2012 from the point of view of molecular design correlated with photovoltaic performance.