Formation and characterization of PbxCd1-xS interlayer for PbSCdSZnS quantum dot sensitized solar cells
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Date
2014-08-01
Authors
Quah Ai Li
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Abstract
Quantum dot sensitized solar cells (QDSSCs) have low efficiency due to the recombinations at electrolyte-electrode interfaces. Lead sulphide (PbS) quantum dots (QDs), lead cadmium sulphide (PbxCd1-xS) QDs, cadmium sulphide (CdS) QDs and followed by coating with zinc sulphide (ZnS) were deposited on TiO2 electrode as TiO2 mesoporous photoanode using successive ionic layer adsorption and reaction (SILAR) method for QDSSCs. PbxCd1-xS QDs deposited between PbS core and CdS shell layer could reduce the recombination and improve the efficiency. TiO2 electrode was formed with the deposition of TiO2 mesoporous film on fluorine doped tin oxide glass (FTO) after calcination at 450 °C. The PbS QDs, PbxCd1-xS QDs, CdS QDs and coating with ZnS were formed on TiO2 electrode with SILAR method. Solar cells were prepared by sandwiching the TiO2 mesoporous photoanode with Cu2S counter electrode. Six SILAR cycles of PbS, CdS, ZnS and PbxCd1-xS as well as multilayer of PbS/CdS/ZnS and PbS/PbxCd1-xS/CdS/ZnS were prepared for characterizations. In multilayer of PbS/PbxCd1-xS/CdS/ZnS, the effects of number of SILAR cycles of PbxCd1-xS were studied with four different molar fraction, x of 0.05, 0.1, 0.15 and 0.2. From current-density voltage (J-V) measurement, four SILAR cycles of PbxCd1-xS interlayer with molar fraction, x of 0.05 in multilayer PbS/PbxCd1-xS/CdS/ZnS samples showed 38.2 % improvement in the efficiency when compared to the multilayer PbS/CdS/ZnS sample. This was because the band gap value obtained for four SILAR cycles of PbxCd1-xS interlayer with molar fraction, x of 0.05 were between band gap value of PbS core and CdS shell layer during UV-Vis spectrometer analysis. Moreover, the traps states were reduced between the PbS core and CdS shell layers with the deposition of PbxCd1-xS interlayer in multilayer of PbS/PbxCd1-xS/CdS/ZnS sample. Among the multilayer PbS/PbxCd1-xS/CdS/ZnS samples, four SILAR cycles of PbxCd1-xS interlayer with molar fraction, x of 0.05 provided the highest efficiency of 0.34 % when compared with four SILAR cycles of PbxCd1-xS interlayer with molar fraction, x of 0.1, 0.15 and 0.2. This is due to the conduction band of four SILAR cycles of PbxCd1-xS interlayer with molar fraction, x of 0.05 was higher and lead to faster electron injection from the conduction band of PbS/PbxCd1-xS to the TiO2 electrode. Thus, lower recombination was obtained and the efficiency was improved. Besides that, four SILAR cycles PbxCd1-xS interlayer showed higher efficiency than six SILAR cycles of PbxCd1-xS interlayer in samples with multilayer PbS/PbxCd1-xS/CdS/ZnS. This was owing to the high loading of PbxCd1-xS QDs with six SILAR cycles of PbxCd1-xS interlayer would prevent the penetration of electrolyte and decreased the efficiency in J-V measurement.