Controlling the Electrical Properties of Undoped and Ta-doped TiO2 Polycrystalline Films via Ultra-Fast Annealing Treatments

TL;DR

This study demonstrates that ultra-fast annealing can rapidly produce highly conductive, transparent TiO2 thin films with controlled electrical properties, significantly reducing processing time compared to traditional methods.

Contribution

It introduces a novel ultra-fast annealing process for TiO2 films that achieves high conductivity and transparency in just 5 minutes, enabling efficient fabrication of functional layers for solar cells.

Findings

Ultra-fast annealing reduces crystallization time from 180 to 5 minutes.

Superficial oxygen incorporation negatively impacts conductivity.

High transparency (~81%) and low resistivity (~6×10^{-4} Ωcm) achieved in TiO2 films.

Abstract

We present a study on the crystallization process of undoped and Ta doped TiO2 amorphous thin films. In particular, the effect of ultra-fast annealing treatments in environments characterized by different oxygen concentrations is investigated via in-situ resistance measurements. The accurate examination of the key parameters involved in this process allows us to reduce the time needed to obtain highly conducting and transparent polycrystalline thin films (resistivity about $6 \times 10^{-4}$ {\Omega}cm, mean transmittance in the visible range about $81\%$) to just 5 minutes (with respect to the 180 minutes required for a standard vacuum annealing treatment) in nitrogen atmosphere (20 ppm oxygen concentration) at ambient pressure. Experimental evidence of superficial oxygen incorporation in the thin films and its detrimental role for the conductivity are obtained by employing different concentrations of traceable 18O isotopes during ultra-fast annealing treatments. The results are discussed in view of the possible implementation of the ultra-fast annealing process for TiO2-based transparent conducting oxides as well as electron selective layers in solar cell devices; taking advantage of the high control of the ultra-fast crystallization processes which has been achieved, these two functional layers are shown to be obtainable from the crystallization of a single homogeneous thin film.