Modification And Application Of SnO₂ Photoanodes In Dye Sensitized Solar Cells

Due to the low cost and simple prepareation process, dye sensitized solar cells（DSSC） has a very promising prospect. SnO₂ is suitable for photoanode material in DSSC with high electron mobility（100-200cm2 V-1 S-1） and wide band gap（3.6eV）. However, DSSC based on the SnO₂ photoanode material has two major disadvantages: the low conduction band position of the SnO₂ lead to the open circuit voltage little. The dark current is large because of the electron recombination fast between the electrolyte and SnO₂. Based on this, in order to improve the performance of dye-sensitized solar cells（DSSC） based on SnO₂ photoanode material, two kinds of modification methods of doping SnO₂ with metal cations and coating SnO₂ with metal oxide thin layers were used. In this paper, we studied Bi-doped SnO₂ particles and Al-doped SnO₂ hollow microspheres and ZnO-coated SnO₂ particles. The photoanode of DSSC were prepared by doctor-blade technique and electrophoretic deposition method based on FTO. The details of the experiment are as follows:Bi-doped SnO₂ particles were used in DSSC as photoanode material. First, the Bi-doped SnO₂ nanoparticles prepared by co-precipitation and used the doctor-blade technique preparation of Bi-doped SnO₂ electrode films. Finally, the DSSCs were sensitized with the dye of N719. XRD results of SnO₂ nanoparticles showed that there were no change of rutile SnO₂ after Bi doped. The photoelectric performance of the results can be clearly seen that the open circuit voltage of DSSC with Bi compared to that of DSSC without Bi had increased significantly from 373 mV to 498 mV, the photoelectric conversion efficiency increased from 1.37% to 2.03%. The photoelectric properties of Bi-doped Sn O2 DSSC were better due to the decrease of the dark current of the DSSC. At the same time, the photoelectron recombination between the working electrode and the electrolyte interface was suppressed.The hydrothermal method was used to synthesis Al-doped SnO₂ hollow microspheres and the photoanode was prepared by doctor-blade technique. The SEM and TEM photographs showed that the Al-doped SnO₂ hollow microspheres were synthesized successfully. XRD showed that there were no effect on the lattice structure of SnO₂ after Al doping. J-V curves showed that Al-doping improved the performance of DSSC. The Jsc and Voc increased from 8.05 mA cm-2 to 11.48 mA cm-2, and from 179 mV to 474 mV, respectively. the photoelectric conversion efficiency also rised from 0.46% to 3.04%. This was due to Al doping inhibited the recombination reaction of photoelectron between the interface of working electrode and electrolyte and extended the electron lifetime.At room temperature ZnO-coated SnO₂ powder were prepared by a facile method. ZnO-coated SnO₂ workelectrode films based on flexible substrate and FTO substrate were prepared by electrophoretic deposition method. This experiment were optimized as follow: ZnO coating SnO₂ amount, electrophoresis time, the pressure of mechanical compressing film treatment. The performance of DSSC were the best when the ZnCl₂ amount of 0.38 g, electrophoresis time of 4min, the pressure of mechanical compressing film treatment for 10 MPa. The current density, open circuit voltage, fill factor, photoelectric conversion efficiency of the battery were 16.43 mA cm-2, 493 mV, 0.49, 3.95%, respectively.In general, Bi-doped SnO₂ particles, Al-doped SnO₂ hollow spheres and ZnO-coated SnO₂ powder were used as photoanodes of DSSC respectively in this paper. The materials of photoanode were optimized, and higher photoelectric conversion efficiency were obtained finally.