Modification of Nanostructured TiO2 Electrodes by Electrochemical Al3+ Insertion: Effects on Dye-Sensitized Solar Cell Performance

Abstract

Nanostructured TiO2 films were modified by insertion with Al ions using an electrochem. process. After heat treatment these films were suitable as electrodes in dye-sensitized solar cells. By a catechol adsorption test and with photoelectron spectroscopy , the d. of Ti atoms at the metal oxide/electrolyte interface decreased due to Al modification. There is not a complete coverage of Al oxide onto the TiO2 - the results suggest either the formation of a mixed Al-Ti oxide surface layer or formation of a partial Al oxide coating. No new phase was detected. In solar cells with Al-modified TiO2 electrodes electron lifetimes and electron transport times increased. At high concns. of inserted Al ions, the quantum efficiency for electron injection decreased. Results are discussed according to a multiple trapping model which can explain slower kinetics by the creation of addnl. traps during Al insertion, and a surface layer model which explains the reduced recombination rate as well as the reduced injection efficiency by the formation of a blocking layer.