… The effect size of CdS Quantum Dots (QDs) on thermal and photovoltaic parameters is investigated. CdS QDs were adsorbed onto TiO2 electrodes using successive ionic layer adsorption and reaction (SILAR) to act as sensitizers of quantum dots solar cells (QDSSCs). The CdS QDs sizes are estimated using optical absorption spectra and application of effective mass approximation model (EMA) as well as high resolution transmission microscopes (HRTEM). The ratio of TiO2/CdS was confirmed by energy dispersive X-ray spectroscopy (EDX). Thermal parameters (thermal diffusivity α, thermal effusivity e and thermal conductivity k are measured by using Photoacoustic (PA) Technique. The photovoltaic parameters (open circuit voltage Voc, short circuit current density Jsc, fill factor FF and efficiency η) of the assembled CdS QDs sensitized solar cells (QDSSCs) were determined under a solar illumination of 100 mW/cm2 (AM 1.5 conditions. Our results show that both the effective thermal conductivity keff and efficiency η of CdS QDs deposited on TiO2 increase as the size of CdS QDs is increased.