Quantum dot sensitized solar cells based on an optimized combination of ZnS, CdS and CdSe with CoS and CuS counter electrodes

[Display omitted] ► Optimization of quantum dot sensitized solar cells. ► Combination of CdS, CdSe and ZnS deposited on nanocrystalline titania. ► Nanostructured metal sulfides employed as counter electrodes. ► Importance of materials deposition sequence. Quantum dot sensitized solar cells have been constructed using photoanodes made of nanocrystalline titania and an optimized combination of ZnS, CdS and CdSe nanoparticles. Pt, CoS and CuS have been used as electrocatalysts on counter electrodes. Attachment of quantum dot sensitizers on mesoporous titania was made by successive ionic layer adsorption and reaction and by chemical bath deposition obeying a certain order, where the first layer was crucial in defining the quality and the quantity of the subsequent layers as well as of the ensuing solar conversion efficiency. Thus the first quantum dot layer consisted of 75% CdS and 25% ZnS and it was followed by a CdSe layer and by an additional ZnS layer on the top. The quantity of material deposition seems to be affected not only by the employed deposition method but also and mainly by the nature of the underlying layer. Optimized anode electrodes led to solar cells producing high current densities but did not much affect open-circuit voltage. The maximum solar conversion efficiency reached in this work was 2.7% and was obtained by using CuS electrocatalyst. Both CoS and CuS gave high currents and this was in line with the low charge transfer resistances recorded in their case.