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