Parametric optimization in quantum dot-sensitized solar cells for efficiency enhancement / Jun Hieng Kiat

CdS and CdSe quantum dots (QDs) which have excellent optical properties were used as sensitizer for the application in solar cells. CdS and CdSe quantum dot-sensitized solar cells (QDSSCs) were fabricated and studied for determining the optimum preparation parameters that produce the best cell performance. CdS and CdSe QD-sensitized TiO2 electrodes were prepared by successive ionic layer adsorption and reaction (SILAR) method. Three preparation parameters were optimized for QD fabrication: concentration of precursor solutions, number of dipping cycles and dipping time per cycle in each solution. CdS QDSSC achieved optimum performance when the QDs were prepared with preparation parameter of 0.10 M precursor solution concentration and 4 dipping cycles with 5 minutes dipping time in each solution. For CdSe QDSSC, optimum performance was achieved when QDs were prepared from 0.03 M precursor solution concentration and 7 dipping cycles with each dipping lasted for 30 seconds. The performance of CdSe QDSSC was further improved with an improved polysulfide electrolyte. A suitable polysulfide electrolyte for CdSe QDSSC composed of 0.5 M Na2S, 0.1 M S and 0.05 M GuSCN. The effect of counter electrode materials were also explored. It was found that both CdS and CdSe QDSSCs performed best when carbon and commercial platinum catalyst were used as their counter electrodes respectively. When a passivation layer of ZnS was applied on the working electrode, a better performance was observed. However, other Zn chalcogenides (ZnSe and ZnTe) did not produce the same effect due to high electron recombination at the photoanode/electrolyte interface. The best CdSe QDSSC performance was obtained when a 24 μm thick TiO2 was applied with ZnS passivation layer. Its efficiency was 3.05%. For CdS QDSSC, doping with Mn2+ and applied with ZnS passivation layer produced the best efficiency of 1.89%.