Preparation Of SnS And PbS Thin Films And Properties Of Sensitized TiO₂ Solar Cells

Narrow bandgap IV-VI semiconductors have been widely used in fields of solar cel s for their excel ent photoelectric effect. Thereinto, SnS possesses direct band gap of 1.3eV, good absorption of visible light with high theoretical photoelectric efficie nc y. PbS possesses narrow direct bandgap of 0.41 eV and wide exciton Bohr radius of 18 nm and meanwhile PbS quantum dots have the ability of broaden the absorption scope of light. Both SnS and PbS are better choice of sensitizer for quantum dot sensitized solar cel s(QDSSCs).In this thesis, SnS and PbS quantum dot thin films were prepared by an in- situ deposition method using ammonium sulfide as sulfur precursor, ethylene glycol monomethyl ether and 1-butyl alcohol as solvent of cation precursor, tin(II) chloride and lead nitrate as tin precursor and lead precursor, respectively. The effect of process parameters such as composition of cation precursor solvent, concentration of anion precursor, cycle numbers and annealing temperatures on the morphology, structure and optical properties were investigated. Finally, SnS and PbS quantum dot were used to prepare QDSSCs, and sensitization order and cycle numbers were investigated to explore the effect on solar cel s.The experimental results showed that orthogonal SnS and cubic PbS quantum dot thin films could be prepared by the in-situ deposition method. The addition of ethylenediamine affected growth rate of crystal and morphology of thin films. The concentration of ammonium sulfide affected the crystal size and optical properties of thin films. The roughness and thickness of SnS thin films could be controlled by changing cycle numbers. SnS and SnS2 mixture were gotten by annealing. The composition of cation precursor solvent affected viscosity and solubility of Pb(NO 3)2 which further alter the morphology and roughness of PbS thin films. The concentratio n of ammonium sulfide and cycle numbers affected the crystal size and morphology of PbS thin films. The growth rate of both SnS and PbS thin films prepared by the in- situ method is 30nm/cycle.TiO2 porous films were prepared using P25 as materials. SnS/TiO2, PbS/TiO2, SnS/PbS/TiO2 and PbS/SnS/TiO2 solar cells were prepared using Pt as counter electrode, iodine as electrolyte, SnS and PbS quantum dot were prepared by appropriate parameters as discussed previously. The effect of cycle numbers on efficiency of solar cel s was studied. The best efficiency of SnS/TiO2 and PbS/TiO2 solar cells was 0.605% and 0.275% by depositing 20 cycles of SnS quantum dots and 7 cycles of PbS quantum dots, respectively. Double quantum dots co-sensitized solar cel s were explored preliminarily as wel. The result showed that SnS/PbS/TiO2 solar cel s have a low efficiency of 0.008% while PbS/SnS/TiO2 solar cells have a better efficiency of 0.152% by depositing SnS quantum dots for 10 cycles firstly followed by 10 cycles of PbS quantum dots.