Reduction of recombination rates due to volume increasing, annealing, and tetraethoxysilicate treatment in hematite thin films

Abstract

We report on the properties of hematite thin films prepared by spray pyrolysis on fluorine-doped tin oxide (FTO)-coated glass substrates and investigated the effect of the spray volume, tetraethoxysilicate treatment of the hematite, and post-annealing at 500 °C for 2 h with 10 °C/min ramping. Raman spectroscopy confirmed the characteristic Raman spectrum of all the films, while high-resolution confocal Raman microscopy showed a uniform intensity, suggesting a homogeneous coating of the hematite films on the FTO substrates. Ultrafast transient absorption spectroscopy indicates that all three experimental parameters—a larger spray volume, tetraethoxysilicate treatment, and annealing—slowed down electron–hole recombination. Global analysis of the difference absorption data resolved the spectra and associated decay lifetimes of three distinct processes, operating on the ultrafast, tens of picoseconds, and hundreds of picoseconds timescales.