The photovoltaic performance of quantum dot sensitized solar cells (QDSSCs) is limited due to charge recombination processes at the photoelectrode/electrolyte interfaces. We analyzed the effect of Sn4+ ion incorporation into CdS quantum dots (QDs) deposited onto TiO2 substrates in terms of enhancing light absorption and retarding electron-hole recombination at the TiO2/QDs/electrolyte interfaces. Sensitization involved depositing CdS QDs with different Sn4+ concentrations on the surface of TiO2 using a facile and cost-effective successive ionic layer adsorption and reaction (SILAR) method. Optimized photovoltaic performance of Sn-CdS sensitized QDSSCs was explored using CuS counter electrodes (CEs) and a polysulfide electrolyte. Structural and optical studies of the photoanodes revealed that the gaps between CdS nanoparticles were partially filled by Sn4+ ions, which enhanced the light absorption of the solar cell device. Electrochemical impedance spectroscopy (EIS) and open circuit voltage decay (OCVD) tests suggested that Se ions can remarkably retard electron-hole recombination at the interfaces, stimulate electron injection into semiconductor QD layers, and provide long-term electron lifetime to the cells. We found that solar cells based on CdS photoanodes doped with 10% Sn4+ ions exhibited a superior power conversion efficiency (PCE) of 3.22%, open circuit voltage (Voc) of 0.593 V, fill factor (FF) of 0.561, and short-circuit current density Qsc) of 9.68 mA cm(-2) under an air mass coefficient (AM) 1.5 G full sun illumination. These values were much higher than those of QDSSCs based on bare CdS photoanodes (PCE = 2.16%, Voc = 0.552 V, FF = 0.471, and Jsc = 8.31 mA cm(-2)). (C) 2018 Elsevier Inc. All rights reserved.