Achieving a cost-effective synthesis of QDs with superior surface quality will dictate the feasibility of quantum dots in commercial photovoltaic devices. Here we report a simple aqueous synthesis of CdTe quantum dots coated with thin CdS layer in water-ethanol solvent mixture for better surface eminence. Enhanced solubility of capping agent and slow growth rate of CdS over CdTe taking place in water ethanol solvent mixture leads to strain free interface construction resulting in 51% enhancement of Photo Luminescence Quantum Yield. Controlling the solubility and growth rate of CdS coating over CdTe core QDs via ethanol addition exhibits a 28.4% and 44.6% improvement in short circuit current densities and quantum dot sensitized solar cells with a conversion efficiency of 2.5% is achieved. Our results show that mixed solvents can be utilized for optimizing the aqueous synthesis of CdTe/CdS QDs with enhanced optical properties leading to better performing photovoltaic devices.