Highly ordered mesoporous TiO2 modified by CdS, CdSe, and ZnS quantum dots (QDs) was fabricated by successive ionic layer adsorption and reaction (SILAR) method. 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. The CdS, CdSe, and ZnS QDs modification expands the photoresponse range of mesoporous TiO2 from ultraviolet region to visible range, as confirmed by UV-Vis spectrum. Optimized anode electrodes led to solar cells producing high current densities. Pt, CuS, PbS, and Cu2S have been used as electrocatalysts on counter electrodes. The maximum solar conversion efficiency reached in this work was 1.52% and was obtained by using Pt electrocatalyst. CuS, PbS, and Cu2S gave high currents and this was in line with the low charge transfer resistances recorded in their case. 1. Introduction As an alternative to dye molecules, semiconductor quantum dots (QDs) like CdS, CdSe [1], PbS [2], InAs [3], InP [4], and others [5] as well as extremely thin inorganic absorber layers [6, 7] have been used. QDs are very attractive because of their size-dependent optical band gap, the possibility to design hierarchical multilayer absorber structures, and the potential to use them for multiexciton generation from a single photon. One potential method for improving the performance of quantum dots solar cells (QDSSCs) is by constructing desired energy band structures using multiple QDs. Niitsoo and coworkers have firstly demonstrated that a desired cascade structure can be formed by sequential deposition of CdS and CdSe layers onto the TiO2 nanoparticle films [8]. Recently, Lee et al. have also reported a self-assembled TiO2/CdS/CdSe structure that exhibited a significant enhancement in the photocurrent response [9, 10]. In addition, nanostructured CuS, PbS, Cu2S, and Pt have been used as electrocatalysts on the counter electrode. Alternative catalysts have been proposed by several researchers [9–12]. Metal sulfides are considered a good choice. However, their deposition on plain FTO electrodes does not always produce materials with sufficiently high specific surface or with structural stability. In this paper, we studied the effects of comodification by CdS, CdSe, and ZnS QDs on the photovoltaic response of mesoporous TiO2 based QDSSC. The mesoporous TiO2 were treated by SILAR of CdS, CdSe, and ZnS QDs and were used as photoanodes in QDSSC. We demonstrated that the comodified mesoporous TiO2 possesses superior photovoltaic response compared to the single QD sensitized
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