Atomic layer deposited ultra thin HfO2 and Al2O3 interfacial layers for high performance Dye Sensitized Solar Cells

This paper presents the possibility of improving the performance of dye sensitized solar cells (DSSCs) by treating the mesoporous TiO
₂
using ultra thin metal oxides such as hafnium oxide (HfO
₂
) and aluminum oxide (Al
₂
O
₃
) grown by atomic layer deposition (ALD) method. Ultrathin HfO
₂
and Al
₂
O
₃
(few nm in thickness) metal oxide layers affect the density and activity of the interface states at the TiO
₂
/dye/electrolyte interfaces and hence affect the overall performance of DSSCs. Different thicknesses of HfO
₂
and Al
₂
O
₃
layers (5, 10 and 20 ALD cycles) were deposited on the mesoporous TiO
₂
surface prior to dye loading process in fabrication of DSSCs. It was observed that the ALD deposition of ultrathin oxides can significantly improve the performance of DSSCs. Further, it was also observed that the improvement in the DSSC performance highly depends on the thickness of the ALD deposited HfO
₂
and Al
₂
O
₃
films. Compared to a reference DSSC, which did not use an ALD interfacial layer, incorporation of a HfO
₂
(5 cycles) and Al
₂
O
₃
(20 cycles) layers resulted in enhancement of 69 and 10% % enhancement respectively.