Aluminum oxides as alternative building blocks for efficient layer-by-layer blocking layers in Dye-sensitized solar cells.

All inorganic layer-by-layer (LbL) thin films composed by TiO2 nanoparticles and [Al(OH)4]- anions (TiO2/AlOx) as well as Al2O3 and Nb2O5 nanoparticles (Al2O3/Nb2O5) have been deposited to FTO surfaces and applied as blocking layers in DSCs. Structural and morphological characterization of the LbL films by different techniques reveal that in TiO2/AlOx assembly, aluminate anions undergo condensation reactions on the TiO2 surface leading to the formation of highly homogeneous films with unique optical properties. After 25 depositions transmittance losses below 10% in relation to the bare FTO substrate are observed. Electrochemical impedance spectroscopy shows that TiO2/AlOx layers impose an effective barrier for the charge recombination at FTO/electrolyte interface with an electron exchange time constant 50-fold higher than that for bare FTO. As a result, an improvement of 85% in the overall conversion efficiency of DSCs was observed with the employment of TiO2/AlOx blocking layers. Al2O3/Nb2O5 LbL films can also work as blocking layers in DSCs but not as efficient, which is associated with the poor homogeneity of the film and its capacitive behavior. The production of cost-effective blocking layers with a low light scattering in the visible region is an important feature towards the application of DSC in other Building-integrated photovoltaic applications.