Browsing by Author "Lin, Ching"

Now showing 1 - 6 of 6

Coverage Analysis for the Core/Shell Electrode of Dye-Sensitized Solar Cells
(2010-06-03)
Tien, Ta-Chang
;
Pan, Fu-Ming
;
Wang, Lih-Ping
;
Tsai, Feng-Yu
;
Lin, Ching
In this study, we established a core/shell (C/S) model that evaluates the surface coverage of an overlayer deposited on nanoparticles in terms of X-ray photoelectron spectroscopy signals of the nanoparticles. We used the model to estimate the coverage of Al(2)O(3) shell layers, which were deposited on the nanoporous TiO(2) electrodes of dye-sensitized solar cells (DSSCs) by atomic layer deposition (ALD), as a function of the number of ALD reaction cycles. The surface coverage increased with the average thickness of the Al(2)O(3) shell layers, indicating that the ALD Al(2)O(3) deposition on the nanoporous electrode was via the island growth mode. The power conversion efficiency of the DSSCs was highest after the first ALD reaction cycle for the Al(2)O(3) shell layers, which had a coverage of 0.25, according to the C/S model. The study shows that, to further improve the PCE, optimization of the ALD Al(2)O(3) deposition condition is required so that the surface coverage of the shell layer can be increased at the first ALD reaction cycle.
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.
Growth mode transition of atomic layer deposited Al2O3 on porous TiO2 electrodes of dye-sensitized solar cells
(2012-01-01)
Tien, Ta-Chang
;
Pan, Fu-Ming
;
Wang, Lih-Ping
;
Tsai, Feng-Yu
;
Lin, Ching
This study investigates the growth behavior of atomic-layer-deposited (ALD) Al2O3 overlayers on porous TiO2 electrodes, which comprise an anatase nanoparticle layer and a rutile particle layer, for optimizing dye-sensitized solar cells. The growth mode of the AID Al2O3 overlayers changes from island growth to layer-by-layer growth during the first few MD reaction cycles, and the growth mode transition is much more pronounced for the anatase electrode layer. The transition is likely a result of the reduction in the contractive lattice strain of the TiO2 nanoparticles. The lattice strain in the hydroxylated TiO2 nanoparticles is progressively reduced during the ALD Al2O3 deposition, resulting in the growth mode transition. (c) 2011 Elsevier B.V. All rights reserved.
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.