Correlation between Energy and Spatial Distribution of Intragap Trap States in the TiO2 Photoanode of Dye-Sensitized Solar Cells.
The energy and spatial distribution of intragap trap states of the TiO2 photoanode of dye-sensitized solar cells and their impact on charge recombination were investigated by means of time-resolved charge extraction (TRCE) and transient photovoltage (TPV). The photoanodes were built from TiO2 nanospheroids with different aspect ratios, and the TRCE results allowed differentiation of two different types of trap states, that is, deep and shallow ones at the surface and in the bulk of the TiO2 particles, respectively. These trap states exhibit distinctly different characteristic energy with only a slight variation in the particle size, as derived from the results of the density of states. Analyses of the size-dependent TPV kinetics revealed that in a moderate photovoltage regime of about 375-625 mV, the dynamics of electron recombination are dominated by shallow trap states in the bulk, which can be well accounted for by the mechanism of multiple-trap-limited charge transport.
Department of Chemistry, Renmin University of China, Beijing, 100872 (China).
Yi
Y
Wang
College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871 (China).|School of Chemistry and Chemical Engineering, Henan Normal University, Henan Xinxiang, 453007 (China).
Dapeng
D
Wu
Department of Chemistry, Renmin University of China, Beijing, 100872 (China).
Li-Min
LM
Fu
Department of Chemistry, Renmin University of China, Beijing, 100872 (China). jpzhang@chem.ruc.edu.cn.
Xi-Cheng
XC
Ai
College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871 (China).
Dongsheng
D
Xu
Department of Chemistry, Renmin University of China, Beijing, 100872 (China). xcai@chem.ruc.edu.cn.
Jian-Ping
JP
Zhang
charge recombination; chemical capacitance; dye-sensitized solar cells; electron transport; sensitizers