Research Of Dye-Sensitized Solar Cells Based On Composite Photoanode

The solar energy application based on solar photovoltaic technology is changing the structure of human energy consuming revolutionarily. The current mainstream solar cell products are silicon-based solar cells, but it has the diasdvantage of high cost and raw materials shortage. Due to the low cost, abundant resources, stable performance, simple production process, nontoxic, pollution-free and suitability for mass production and other advantages, dye-sensitized solar cells (DSSC) is likely to replace silicon solar cells, dominating solar cells field in the foreseeable future. This thesis focuses on the TiO2 nanoparticles/nanowires and ZnO/TiO2 composites photoanodes of dye-sensitized solar cell preparation, photovoltaic and electrochemical properties, and its specific contents are as follows:Study based on TiO2 nanoparticles/nanowires composite photoanode of dye-sensitized solar cells. TiO2 nanowires powder were synthesized by hydrothermal method. Tetrabutyl titanate sol was prepared from sol-gel process. Gel slurry was formated by Tetrabutyl titanate sol mixing with TiO2 nanowires powder. The composites photoanode of TiO2 nanoparticles and TiO2 nanowires were prepared on transparent conductive fluorine-doped tin oxide (FTO) substrates by dip-coating method. The structure and morphology characteristics of TiO2 nanowires powder and composites photoanode have been analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM). The effect of the relative nanowire/nanoparticle ratio on the performance of solar cells were systematically investigated by J-V curves and electrochemical impedance spectroscope. The results showed that the distribution of TiO2 nanowires in TiO2 nanoparticles/nanowires composite films was relatively uniform, forming inter-connected network structure; with the increase of TiO2 nanowires addition, the short-circuit current density increased from 1.84mA/cm2 to 13.50mA/cm2 and the light-to-electricity efficiency of DSSC from 0.85% to 6.61%, while open-circuit voltage and fill factor basically remained constant.Study based on ZnO/TiO2 composite photoanode of dye-sensitized solar cells. ZnO microrods were synthesized by low temperature solution-phase method. ZnO/TiO2 composites photoanodes were prepared on FTO with pastes of different proportion of ZnO microrods and TiO2 nanopowders by doctor-blade method. The effect of the relative microwire/nanoparticle ratio on the performance of solar cells were systematically investigated by J-V curves and electrochemical impedance spectroscope. The results show that the solar conversion efficiency of the dye sensitized solar cells after the addition of ZnO microrods (50 wt%) was increased by about 30% compared to that pure TiO2 photoanode. This is mainly because of the ZnO microrods having higher photon absorption and a good electron transfer properties.Analysis of electrochemical impedance spectroscopy of DSSC. Electrochemical impedance spectroscopy was employed to study the impedance characteristic of DSSC in the process of electron transfer. Based on the impedance spectroscopies tested under different positive/negative bias, together with the working principle of DSSC, the corresponding equivalent circuit model was established. The practically-measured impedance spectroscopies were fitted by using this model, and the fitting results matched well with the practical measurement, the values for the parameters of the components in the equivalent circuit were reasonable, indicating the reasonability of the model. The inner impedance distribution was analyzed as well. The results indicated that the whole inner impedance was mainly attributed to the transfer impedance of electrons in the photoanode and the interface between photoanode/dye/electrolyte. With the increase of nanowire addition in TiO2 nanoparticle/nanowire composite photoanode of DSSC, the transfer impedance of electrons in the photoanode and the interface between photoanode/dye/electrolyte decreased obviously. In ZnO/TiO2 composite photoanode of DSSC, the curves in middle frequency range indicated the characteristic frequency of electron transfer in photoanode decreased as the increase of ZnO content.