title: Interfacial energy levels and related properties of atomic-layer-deposited Al2O3 films on nanoporous TiO2 electrodes of dye-sensitized solar cells.
abstract: Low-temperature (approximately 150 degrees C), atomic-layer-deposited Al(2)O(3) 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 Al(2)O(3) with a thickness of approximately 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 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 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 TiO2 solar cells.
authors: Department of Material Science and Engineering, National Chiao Tung University, 300, Taiwan, Republic of China. tien@itri.org.tw
authors: Ta-Chang
authors: TC
authors: Tien
authors: Fu-Ming
authors: FM
authors: Pan
authors: Lih-Ping
authors: LP
authors: Wang
authors: Chia-Hua
authors: CH
authors: Lee
authors: Yung-Liang
authors: YL
authors: Tung
authors: Song-Yeu
authors: SY
authors: Tsai
authors: Ching
authors: C
authors: Lin
authors: Feng-Yu
authors: FY
authors: Tsai
authors: Su-Jen
authors: SJ
authors: Chen