Ultra-fast sintered TiO2 films in dye-sensitized solar cells: phase variation, electron transport and recombination

Abstract

With the application of near-infrared radiation (NIR), TiO₂ films for dye-sensitized solar cells (DSCs) on metallic substrates can be sintered in just 12.5 seconds. The photovoltaic performance of devices made with NIR sintered films match those devices made with conventionally sintered films prepared by heating for 1800 seconds. Here we characterise the electron transport, electron lifetime and phase-morphological properties of ultrafast NIR sintered films, using impedance spectroscopy, transient photovoltage decay and X-ray diffraction measurements. An important factor in NIR processing of TiO₂ films is the peak metal temperature (PMT) and we show that during the 12.5 second heat treatment, a PMT of around 635 °C gives near identical electron transport, electron lifetime and morphological properties, as well comparable photovoltaic performance to a conventionally sintered (500 °C, 30 min) film. We demonstrate that the rapid heating of the TiO₂ (to temperatures of up to 785 °C) does not lead to a large scale rutile phase transition. As such photovoltaic performance of resultant DSC devices is maintained since the heating period is insufficient to induce a significant transition from anatase to rutile or morphology changes which result in a loss of photocurrent.