Photocathode studies for quantum dots sensitized solar cells
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Date
2016-06
Authors
Ch’ng Mun Sunn
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Abstract
Photocathodes or counter electrodes (CE) plays an important role involving electron transfer and catalysing reduction reaction of the electrolyte in Quantum Dot Sensitized Solar Cells (QDSSCs). Different counter electrode (CE) materials based on platinum (Pt), silver (Ag), gold nanoparticles (AuNPs), graphene nanoplatelets (GNPs) and brass/Cu2S were prepared for the application in CdS/ZnS QDSSCs. Successive Ionic Layer Adsorption and Reaction (SILAR) method was used for photoanode preparation. While all of the counter electrodes were prepared using low-cost and facile methods such as doctor blade technique (for Pt and Ag), drop casting method (for AuNPs), solvent interface method (for GNPs) and hydrochloric acid (HCl) solution immersion (for brass/Cu2S). The effect of brass/Cu2S CE with different HCl immersion time and different HCl immersion temperature were studied respectively. Besides, the surface structure, cross sectional morphologies, surface topography and surface roughness of all the counter electrodes were investigated and their power conversion efficiency (η) and internal resistances were measured. Brass/Cu2S CE with immersion temperature of 60 °C in HCl solution for 45 minutes produced the highest solar cell performance (η = 0.70 %) in CdS/ZnS QDSSCs, while carbon-based material such as graphene nanoplatelets (GNPs) produced the lowest performance (η = 0.03 %). Metallic-based material such as platinum (Pt), silver (Ag) and gold nanoparticles (AuNPs) were less superior than brass/Cu2S CE. The poor performance of QDSSCs with some CE materials was largely due to the lower photocurrent density and opencircuit voltage. The Electrochemical Impedance Spectroscopy (EIS) performed on the cells showed that the high-performing QDSSCs had lower charge-transfer resistances (Rct) and lower sum of resistances (Rsum) at their CE/electrolyte interfaces.