The photovoltaic performance of CdTe quantum dots (QDs) sensitized solar cells (QDSSCs) as a function of tuning the band gap of CdTe QDs size is studied. The tuning of band gap was carried out through controlling the size of QDs. Presynthesized CdTe QDs of radii from 2.1 nm to 2.5 nm) were deposited by direct adsorption (DA) technique onto a layer of TiO2 nanoparticles (NPs) to serve as sensitizers for the solar cells. The characteristic parameters of the assembled QDSSCs were measured under AM 1.5 sun illuminations. The values of current density (J(sc)) and overall efficiency (eta) increase with decreasing CdTe QDs size, since the lowest unoccupied molecular orbital (LUMO) levels shifts closer to vacuum level, which causes an increase in the driving force. Consequently the electrons' injections to the conduction band (CB) of TiO2 NPs become faster. The maximum values of J(sc) (1105 mu A/cm(2)) and eta (0.190%) were obtained for the smallest CdTe QDs size (2.10 nm). The open circuit voltages (V-oc) varies slightly with the size of the CdTe QDs, however it is only dictated by the CB level of TiO2 NPs and the VB of the electrolyte. Furthermore, the photocurrent response of the assembled cells to ON-OFF cycles of the illumination indicates the prompt generation of anodic current. (c) 2012 Elsevier Ltd. All rights reserved.