Overview of atomic layer deposited metal oxides for treating nanoporous TiO2 photoelectrode for dye sensitized solar cells

Atomic layer deposited (ALD) ultrathin metal oxides, HfO₂, Al₂O₃ and SiO₂, were used to treat the surface of nanoporous TiO2 for dye sensitized solar cell (DSSC) application. X ray photoelectron spectroscopy was performed to probe the growth of metal oxides on TiO₂ surface. ALD grown metal oxide layers on TiO₂ surface did not block the porosity as observed in atomic force microscopic studies. Conformal surface coverage was achieved as shown by high resolution transmission electron microscopic analysis on ALD grown TiO₂ and the thickness was about 2 nm. It was observed that performance of DSSC was significantly enhanced by ALD metal oxide surface treatment. The enhanced DSSC performance asserted that electron injection from the dye to TiO₂ was not blocked while the electron trap from the conduction band of TiO₂ to surface states was significantly suppressed and hence the improved performance. Further, it was noticed that the thickness of ALD metal oxide layers play a vital role in the photovoltaic performance of DSSCs.