Browsing by Author "Tsai, Song-Yeu"

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Dye-sensitized solar cells with a micro-porous TiO(2) electrode and gel polymer electrolytes prepared by in situ cross-link reaction
(2009-11-01)
Lee, Kun-Mu
;
Hsu, Chih-Yu
;
Chiu, Wei-Hao
;
Tsui, Meng-Chin
;
Tung, Yung-Liang
The ionic conductivities and performances of dye-sensitized solar cells(DSSCs) of gel polymer electrolytes(GPEs) prepared by in situ cross-link reaction with different cross-linkers were investigated. The poly(imidazole-co-butylmethacrylate)-based GPE containing the 1,2,4,5-tetrakis(bromomethyl)benzene (B4Br) cross-linker showed a higher ionic conductivity than that containing cross-linkers with a linear structure, due to the formation of micro-phase separation that resulted in an increase in ion transport paths in the GPE. Moreover, the co-adsorbent((4-pyridylthio) acetic acid, PAA) co-adsorbed with N3 dye on the TiO(2) electrode not only reduced dye aggregation, but also reacted with the cross linkers in the GPE at the TiO(2)/GPE interface. A decrease in the charge transport resistance at the TiO2/GPE interface was noted after forming the gel; thus the value of J(SC) significantly increased from 7.72 to 10.00 m A cm(-2). In addition, in order to reduce the ionic diffusion resistance within the TiO(2) electrode, incorporation of monodispersed PMMA in the TiO(2) paste was considered. With the optimal weight ratio of PMMA/TiO(2) (w/w 3.75), the TiO(2) electrode exhibited larger pores (ca. 350 nm) uniformly distributed afters intering at 500 degrees C, and the ionic diffusion resistance within the TiO2 film could significantly be reduced. The cell conversion efficiency increased from 3.61% to 5.81% under illumination of 100 mW cm (-2), an improvement of ca. 55%. (C) 2009 Elsevier B. V. All rights reserved.
Dye-sensitized solar cells with a micro-porous TiO2 electrode and gel polymer electrolytes prepared by in situ cross-link reaction
(2009-11-01)
Lee, Kun-Mu
;
Hsu, Chih-Yu
;
Chiu, Wei-Hao
;
Tsui, Meng-Chin
;
Tung, Yung-Liang
The ionic conductivities and performances of dye-sensitized solar cells(DSSCs) of gel polymer electrolytes(GPEs) prepared by in situ cross-link reaction with different cross-linkers were investigated. The poly(imidazole-co-butylmethacrylate)-based GPE containing the 1,2,4,5-tetrakis(bromomethyl)benzene (B4Br) cross-linker showed a higher ionic conductivity than that containing cross-linkers with a linear structure, due to the formation of micro-phase separation that resulted in an increase in ion transport paths in the GPE. Moreover, the co-adsorbent((4-pyridylthio) acetic acid, PAA) co-adsorbed with N3 dye on the TiO2 electrode not only reduced dye aggregation, but also reacted with the cross linkers in the GPE at the TiO2/GPE interface. A decrease in the charge transport resistance at the TiO2/GPE interface was noted after forming the gel; thus the value of J(SC) significantly increased from 7.72 to 10.00 m A cm(-2). In addition, in order to reduce the ionic diffusion resistance within the TiO2 electrode, incorporation of monodispersed PMMA in the TiO2 paste was considered. With the optimal weight ratio of PMMA/TiO2 (w/w 3.75), the TiO2 electrode exhibited larger pores (ca. 350 nm) uniformly distributed afters intering at 500 degrees C, and the ionic diffusion resistance within the TiO2 film could significantly be reduced. The cell conversion efficiency increased from 3.61% to 5.81% under illumination of 100 mW cm (-2), an improvement of ca. 55%. (C) 2009 Elsevier B. V. All rights reserved.
Enhanced performance of dye-sensitized solar cells by an Al(2)O(3) charge-recombination barrier formed by low-temperature atomic layer deposition
(2009-01-01)
Lin, Ching
;
Tsai, Feng-Yu
;
Lee, Min-Hsueh
;
Lee, Chia-Hua
;
Tien, Ta-Chang
Al(2)O(3) films are deposited conformally and uniformly by atomic layer deposition (ALD) at 150 degrees C throughout the surface of the nanoporous TiO(2) electrode of dye-sensitized solar cells (DSSCs) to serve as charge recombination barriers (CRB). The self-limiting film growth of ALD enables detailed analysis of the thickness dependence of the CRB effects on the DSSCs, revealing the optimal Al(2)O(3) CRB thickness to be that produced by 1 ALD cycle (nominal thickness - 0.1 nm), at which the CRB increases the power conversion efficiency (PCE) of the DSSCs by 14% (to up to 7.8% PCE). Above 1 cycle, the ALD films excessively raise the Fermi level of the TiO(2) electrode surface, as determined by ultraviolet photoelectron spectroscopy (UPS), so as to block electron injection at the dye-to-TiO(2) heterojunction and to cause significant degradation in the DSSC performance. Instead of its nominal 0.1 nm thickness, the 1-cycle ALD film has an effective CRB thickness of 0.3 nm because of steric hindrance among the ALD precursor molecules and the dye molecules, as analyzed by a graphical model. The optimal thickness of the ALD Al(2)O(3) CRB is considerably thinner than the 0.9-2.5 nm reported for Al(2)O(3) CRB formed by conventional sol-gel processes, but it should better reflect the true value, considering the better infiltrating capability and finer thickness resolution of the ALD films. The low temperature and fine thickness control of the ALD process will broaden the utility of CRB.
Enhanced performance of dye-sensitized solar cells by an Al2O3 charge-recombination barrier formed by low-temperature atomic layer deposition
(2009-01-01)
Lin, Ching
;
Tsai, Feng-Yu
;
Lee, Min-Hsueh
;
Lee, Chia-Hua
;
Tien, Ta-Chang
Al2O3 films are deposited conformally and uniformly by atomic layer deposition (ALD) at 150 degrees C throughout the surface of the nanoporous TiO2 electrode of dye-sensitized solar cells (DSSCs) to serve as charge recombination barriers (CRB). The self-limiting film growth of ALD enables detailed analysis of the thickness dependence of the CRB effects on the DSSCs, revealing the optimal Al2O3 CRB thickness to be that produced by 1 ALD cycle (nominal thickness - 0.1 nm), at which the CRB increases the power conversion efficiency (PCE) of the DSSCs by 14% (to up to 7.8% PCE). Above 1 cycle, the ALD films excessively raise the Fermi level of the TiO2 electrode surface, as determined by ultraviolet photoelectron spectroscopy (UPS), so as to block electron injection at the dye-to-TiO2 heterojunction and to cause significant degradation in the DSSC performance. Instead of its nominal 0.1 nm thickness, the 1-cycle ALD film has an effective CRB thickness of 0.3 nm because of steric hindrance among the ALD precursor molecules and the dye molecules, as analyzed by a graphical model. The optimal thickness of the ALD Al2O3 CRB is considerably thinner than the 0.9-2.5 nm reported for Al2O3 CRB formed by conventional sol-gel processes, but it should better reflect the true value, considering the better infiltrating capability and finer thickness resolution of the ALD films. The low temperature and fine thickness control of the ALD process will broaden the utility of CRB.
Formation of Branched ZnO Nanowires from Solvothermal Method and Dye-Sensitized Solar Cells Applications
(2008-10-01)
Cheng, Hsin-Ming
;
Chiu, Wei-Hao
;
Lee, Chia-Hua
;
Tsai, Song-Yeu
;
Hsieh, Wen-Feng
Branched ZnO nanowires have been fabricated on conductive glass substrates via a solvothermal method for dye-sensitized solar cells (DSCs). The 1D branched nanostructures can afford a direct conduction pathway instead of interparticle hops while using nanoparticles. Furthermore, the short-circuit current density and the energy conversion efficiency of the branched ZnO nanowire DSCs are 4.27 mA/cm(2) and 1.51%,which are twice as high as the bare ZnO nanowire ones. The improvement was a consequence of the enlargement of the internal surface area within the photoelectrode and allowed us to achieve higher dye adsorption to significantly enhance the performance of the DSCs.
Interfacial energy levels and related properties of atomic-layer-deposited Al(2)O(3) films on nanoporous TiO(2) electrodes of dye-sensitized solar cells
(2009-07-29)
Tien, Ta-Chang
;
Pan, Fu-Ming
;
Wang, Lih-Ping
;
Lee, Chia-Hua
;
Tung, Yung-Liang
Low-temperature (similar to 150 degrees C), atomic-layer-deposited Al(2)O(3) films on nanoporous TiO(2) electrodes of dye-sensitized solar cells (DSSCs) were investigated using electron spectroscopy. The power conversion efficiency (PCE) of the DSSCs was increased from 5.7% to 6.5%, an improvement of 14%, with one monolayer of Al(2)O(3) with a thickness of similar to 0.2 nm. The formation of Ti-O-Al(OH)(2) and interfacial dipole layers exhibited a strong influence on the work function of the Al(2)O(3) over-layers, while the thicker Al(2)O(3) over-layers caused the values of valence band maximum and band gap to approach the values associated with pure Al(2)O(3). A work function difference (Delta Phi(A-T)) of 0.4 eV and a recombination barrier height (epsilon(RB)) of 0.1 eV were associated with the highest PCE achieved by the first monolayer of the Al(2)O(3) layer. Thicker Al(2)O(3) over-layers, however, caused significant reduction of PCE with negative Delta Phi(T-A) and increased interfacial energy barrier height (*epsilon(IB)) between the N719 dyes and TiO(2) electrodes. It was concluded that the PCE of the DSSCs may correlate with Delta Phi(A-T), epsilon(RB), and *epsilon(IB) resulting from various thicknesses of the Al(2)O(3) over-layers and that interfacial reactions, such as the formation of Ti-O-Al(OH)(2) and dipole layers, play an important role in determining the interfacial energy levels required to achieve optimal performance of dye-sensitized TiO(2) solar cells.
Interfacial energy levels and related properties of atomic-layer-deposited Al2O3 films on nanoporous TiO2 electrodes of dye-sensitized solar cells
(2009-07-29)
Tien, Ta-Chang
;
Pan, Fu-Ming
;
Wang, Lih-Ping
;
Lee, Chia-Hua
;
Tung, Yung-Liang
Low-temperature (similar to 150 degrees C), atomic-layer-deposited Al2O3 films on nanoporous TiO2 electrodes of dye-sensitized solar cells (DSSCs) were investigated using electron spectroscopy. The power conversion efficiency (PCE) of the DSSCs was increased from 5.7% to 6.5%, an improvement of 14%, with one monolayer of Al2O3 with a thickness of similar to 0.2 nm. The formation of Ti-O-Al(OH)(2) and interfacial dipole layers exhibited a strong influence on the work function of the Al2O3 over-layers, while the thicker Al2O3 over-layers caused the values of valence band maximum and band gap to approach the values associated with pure Al2O3. A work function difference (Delta Phi(A-T)) of 0.4 eV and a recombination barrier height (epsilon(RB)) of 0.1 eV were associated with the highest PCE achieved by the first monolayer of the Al2O3 layer. Thicker Al2O3 over-layers, however, caused significant reduction of PCE with negative Delta Phi(T-A) and increased interfacial energy barrier height (*epsilon(IB)) between the N719 dyes and TiO2 electrodes. It was concluded that the PCE of the DSSCs may correlate with Delta Phi(A-T), epsilon(RB), and *epsilon(IB) resulting from various thicknesses of the Al2O3 over-layers and that interfacial reactions, such as the formation of Ti-O-Al(OH)(2) and dipole layers, play an important role in determining the interfacial energy levels required to achieve optimal performance of dye-sensitized TiO2 solar cells.