Selective Synthesis Of FeS And FeS₂ Nanosheet Films On Iron Substrate For Double-photoelectrode Dye-sensitized Solar Cells

There are two critical issues during the 20th century -- the energy crisis and environment pollution.One of the significant ways to solve the energy crisis problem is using solar energy adequately,which is a kind of inexhaustible,renewable and clear energy.The solar cells that can transform solar energy to electrical power had attracted more and more scientific attention.TiO₂ is an inexpensive,safe and widely-used material of solar cells.However,the band gap of TiO₂(3.2 eV)is too wide to absorb the visible light of the sun's irradiation. This character results in its low conversion efficiency.One way to solve this problem is to extend the absorption of TiO₂ to visible light by dye sensitization.Pyrite(FeS₂)is an alternative absorber material for solar cells due to its very high optical absorption coefficient,α= 5×10⁵ cm^<sup>-1forλ≤700 nm,and its suitable bandgap, E_g=0.95 eV,for solar spectrum.In addition,pyrite is composed of very abundant,cheap and nontoxic elements.Specially,its optical absorption coefficient is two orders of magnitude higher than that of crystalline silicon.Iron sulfide,FeS,has attracted considerable attention since the 1950s due to its electrical and magnetic properties.Up to now,a variety of devices are used in order to improve conversion efficiency dye-sensitized solar cells.However,double-photoelectrode systems were few reported in dye-sensitized solar cells.The theoretical upper limit for a tandem device with two photoactive semiconductors is around 43%,much higher than that of the cell with only one photoactive dye-sensitized electrode.An obvious advantage of a double-photoelectrode cell is that the maximum output voltage can be higher. Therefore the double-photoelectrode system could be a potential device for the conversion of light to electricity.In this paper,we prepared the TiO₂ nanorods by a two-phase soft interface method, and manufactured TiO₂ nanorods electrode using a doctor-blade technique.FeS and FeS₂ nanosheets films were synthesized selectively on iron substrates through one-step hydrothermal treatment of iron foils and sulfur powder in the presence and absence of hydrazine.The double-photoelectrode based solar cells composed of dye-sensitized TiO₂ nanorod film as the photoanode and FeSx(x=1,2)nanosheet films as the photocathode were fabricated.The relationship between the performances of the solar cells and different photocathodes were discussed,especially in the aspect of the open-circuit potential.