Abstract
Titanium dioxide (TiO2) thin films are widely employed for photocatalytic and photovoltaic applications where the long lifetime of charge carriers is a paramount requirement for the device efficiency. To ensure the long lifetime, a high temperature treatment is used which restricts the applicability of TiO2 in devices incorporating organic or polymer components. In this study, we exploited low temperature (100–150 °C) atomic layer deposition (ALD) of 30 nm TiO2 thin films from tetrakis(dimethylamido)titanium. The deposition was followed by a heat treatment in air to find the minimum temperature requirements for the film fabrication without compromising the carrier lifetime. Femto-to nanosecond transient absorption spectroscopy was used to determine the lifetimes, and grazing incidence X-ray diffraction was employed for structural analysis. The optimal result was obtained for the TiO2 thin films grown at 150 °C and heat-treated at as low as 300 °C. The deposited thin films were amorphous and crystallized into anatase phase upon heat treatment at 300–500 °C. The average carrier lifetime for amorphous TiO2 is few picoseconds but increases to >400 ps upon crystallization at 500 °C. The samples deposited at 100 °C were also crystallized as anatase but the carrier lifetime was <100 ps.
Highlights
Wide bandgap transition metal oxides (e.g., TiO2, ZnO, SnO2) have broad range of applications in photovoltaics and photocatalytic devices where they supply or deliver charge carriers [1,2]
Titanium dioxide (TiO2) thin films are widely employed for photocatalytic and photovoltaic applications where the long lifetime of charge carriers is a paramount requirement for the device efficiency
Exploitation of these materials is crucial for advancement in many photonic applications like photovoltaics [3,4] photodegradation [5,6] and photocatalysis [7]
Summary
Wide bandgap transition metal oxides (e.g., TiO2, ZnO, SnO2) have broad range of applications in photovoltaics and photocatalytic devices where they supply or deliver charge carriers [1,2]. Metal oxides in practical applications are often polycrystalline or amorphous with high degree of lattice disorder that affects the density of band edge states [8]. These states are defect states that can act as traps and promote the deleterious recombination of charge carriers. In order to improve the performance of TiO2 in photovoltaics and photocatalytic applications, it is paramount requirement that carriers do not recombine rapidly and have sufficient lifetime to diffuse through the TiO2 layer or to be consumed in catalytic reactions [1,13,14]
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