The Preparation And Performance Investigation Of Dye-sensitized Nanocrystalline Solar Cells Based On WO₃

Dye-sensitized nanocrystalline solar cells have attracted much attention because of their simple design and low fabrication cost. The performance of the photoanode has an key role in photoelectrical conversion of the dye-sensitized solar cells. Among various oxide semiconductors, tungsten trioxide (WO3) has good electron transport capability, high chemical stability and excellent photoelectrochemical performance, making it a promising photoanode material. In addition, non-metal doping would increase the optical absorption and improve electron transport capability of WO3, resulting in an increase of the photoelectrochemical performance of WO3and the photoelectrical conversion efficiency in dye-sensitized solar cells.In this paper, nanocrystalline porous WO3films were fabricated from synthesized WO3particles via doctor blade method. By using ammonium metatungstate as the precursor and cetytrimethyl ammonium bromide as a sufactant, WO3nanocrystals with different sizes were prepared through the hydrothermal reaction and post calcination at different temperatures. Then the samples were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and UV-Vis absorption (UV-Vis). The results indicated that particle sizes have an important influence on the photovoltaic performance of nanocrystalline WO3film electrodes. After calcined at650℃, the flat band potential, donor carrier density, and photocurrent density of the nanocrystalline WO3films are0.46V (vs. Ag/AgCl),3.445×1020cm-3and2.50mA/cm2under irradiation with a500W Xe Lamp (I0=100mW/cm2), respectively. N-doped WO3film electrodes were fabricated by doctor blade method using urea as a nitrogen source. The effect of nitrogen content on the photoelectrochemical performance of the WO3films was also investigated. It was found that nitrogen can be doped successfully into WO3crystal lattice, and some oxygen atoms could be substituted by nitrogen element. The N-doped WO3with N/W ratio of1%has a bandgap of2.50eV. In comparison to undoped WO3, the N-doped samples showed a significant enhancement of1.5fold in photoresponse.On the basis of the above investigation, WO3and N-doped WO3nanocrystalline films were used as working electrodes, respectively. The I3-/I-redox couple was used as electrolyte, and the counter electrode was constructed of conducting glass substrates coated with Pt films. The film thickness of WO3on the performance of solar cells were investigated by I-V and photon-to-current conversion efficiency (IPCE) measurements. The results showed that the optimal thickness of both WO3and N-WO3nanocrystalline film was determined to be7μm, and the photoelectric conversion efficiency have reached to19%and28%at500nm wavelength, respectively.