Effect of atomic layer deposited ultra thin HfO2 and Al2O3 interfacial layers on the performance of dye sensitized solar cells

The objective of this work was to investigate the improvement in performance of dye sensitized solar cells (DSSCs) by depositing ultra thin metal oxides (hafnium oxide (HfO2) and aluminum oxide (Al2O3)) on mesoporous TiO2 photoelectrode using atomic layer deposition (ALD) method. Different thicknesses of HfO2 and Al2O3 layers (5, 10 and 20 ALD cycles) were deposited on the mesoporous TiO2 surface prior to dye loading process used for fabrication of DSSCs. It was observed that the ALD deposition of ultrathin oxides significantly improved the performance of DSSCs and that the improvement in the DSSC performance depends on the thickness of the deposited HfO2 and Al2O3 films. Compared to a reference DSSC the incorporation of a HfO2 layer resulted in 69% improvement (from 4.2 to 7.1%) in the efficiency of the cell and incorporation of Al2O3 (20 cycles) resulted in 19% improvement (from 4.2 to 5.0%) in the efficiency of the cell. These results suggest that ultrathin metal oxide layers affect the density and the distribution of interface states at the TiO2/organic dye and TiO2/liquid electrolyte interfaces and hence can be utilized to treat these interfaces in DSSCs.