Abstract
High performance is expected in dye-sensitized solar cells (DSSCs) that utilize one-dimensional (1-D) TiO2 nanostructures owing to the effective electron transport. However, due to the low dye adsorption, mainly because of their smooth surfaces, 1-D TiO2 DSSCs show relatively lower efficiencies than nanoparticle-based ones. Herein, we demonstrate a very simple approach using thick TiO2 electrospun nanofiber films as photoanodes to obtain high conversion efficiency. To improve the performance of the DSCCs, anatase-rutile mixed-phase TiO2 nanofibers are achieved by increasing sintering temperature above 500°C, and very thin ZnO films are deposited by atomic layer deposition (ALD) method as blocking layers. With approximately 40-μm-thick mixed-phase (approximately 15.6 wt.% rutile) TiO2 nanofiber as photoanode and 15-nm-thick compact ZnO film as a blocking layer in DSSC, the photoelectric conversion efficiency and short-circuit current are measured as 8.01% and 17.3 mA cm−2, respectively. Intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy measurements reveal that extremely large electron diffusion length is the key point to support the usage of thick TiO2 nanofibers as photoanodes with very thin ZnO blocking layers to obtain high photocurrents and high conversion efficiencies.
Highlights
Due to their cost-effectiveness, ease of manufacturing, and suitability for large-area production, dye-sensitized solar cells (DSSCs) have attracted much attention
The certified energy conversion efficiency of DSSCs has exceeded 12% [1], electrons generated from photoexcited dyes injected into the conduction band of TiO2 will pass through the grain boundaries and interparticle connections, which are strongly influenced by the surface trapping/detrapping effect, leading to slow electron transport [2]
With the increase of the sintering temperature, some anatase TiO2 grains will transform to rutile ones, which may result in the thinning of the fibers
Summary
Due to their cost-effectiveness, ease of manufacturing, and suitability for large-area production, dye-sensitized solar cells (DSSCs) have attracted much attention. Backside-illumination mode of anodized TiO2 nanotube-based solar cells is an obstacle for realizing a high efficiency since the redox electrolyte containing the iodine species has an absorption in near UV spectrum and platinum-coated fluorine-doped SnO2 (FTO) partially and inevitably reflects light [17,18]. On the contrary, it is very easy within a short period of process to enlarge the thickness of TiO2 electrospun nanofiber photoanode on FTO substrates for front illumination
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