Photoanode Fabrication And Photoelectrical Properties Of TiO₂ Nanostructured Solar Cells

The strategy of sustainable development requirements need us to develop photovoltaic technology to solve energy shortage and pollution problem. Dye sensitized solar cells（DSSCs） and quantum dots sensitized solar cells（QDSCs） have been received more and more extensive concerning due to their low cost and high theoretical solar-to-electricity conversion efficiency.However, the real solar-to-electricity conversion efficiency of solar cells is far behind the the theoretical value,so how to improve the conversion efficiency has been becoming the hot research spot. The photoanode determines the final solar-to-electricity conversion efficiency. One dimensional（1D） structures ensure efficient separation and collection of charge carriers, however, the photovoltaic performance of DSSCs or QDSCs based on 1D nanostructure is limited by its insufficient surface area and large space between adjacent 1D nanostructures resulting in less dyes or QDs loading and poor light harvesting. Therefore, how to optimize the photoanode structure to improve the utilization rate of light and inhibit recombination of electron is the key to improve sensitized solar photoelectric properties. On the other hand, CdS quantum dots sensitized photoanode can not make use of the sunlight effectively, therefore, co-sensitization is an effective method to improve the light harvesting efficiency and final solar-to-electricity conversion efficiency.Based on the problems mentioned above, in our paper, we optimize the photoanode structure by improving TiO₂ nanostructures and adopting the narrow band gap quantum dots, so as to achieve the higher solar-to-electricity conversion efficiency of sensitized solar cells. Specific content can be divided into the following sections:（1）The double layer structure film that consists of TiO₂ microspheres and TiO₂ nanorod arrays（NR） was obtained and applied as photoanode in DSSCs and QDSCs. UV-visible diffuse reflectance spectrum and absorption spectrum confirm that the photoanode based on double layers has large surface area resulting in more dyes or QDs loading and high light scattering property. Moreover, the surface photovoltage（SPV） measurements demonstrate that rutile/anatase heterojunction is favorable for electron transfer from rutile to anatase, resulting in the enhancement of electron collection efficiency and the increasing electron lifetime. As a result, current density of DSSCs and QDSCs based on the double layer exhibited 4 times, 2 times higher than the photoanode based on TiO₂ nanorod arrays（NR） respectively.（2）Due to the photoanode sensitized by Cd S QDs has some defects in electronic transporting, so we loaded CuInS₂ QDs and CdS QDs on H-TiO₂ NRs successively. UV-visible absorption spectrum confirm that the H-TiO₂ NRs photoanode adsorbs more QDs due to the higher specific surface area and has superior light scattering capacity, which are responsible for the improvement of the solar-to-electricity conversion efficiency. What’s more, the incorporation of CuInS₂ as a co-sensitizer and a transition layer between the H-TiO₂ NRs and CdS QDs promote the electron transfer from CdS to TiO₂, which reduces the recombination rate of the electron with the electrolyte. All of the above advantages can get a better conversion efficiency than the CdS QDs single sensitized solar cell, which was 71% improvement over the QDSCs based on TiO₂ NR.