We report a novel and simple method for the synthesis of high quality PbS colloidal quantum dots (CQDs) by controlled precipitation between Pb²⁺ cations and S²⁻ anions inside aqueous nanodroplets that are generated by an ultrasonic bath operated at 35 ​kHz frequency. The synthesized PbS CQDs have cubic crystal structure with an average particle size of 6.8 ​nm, a size dispersion of 15% and an optical band gap of 0.72 ​eV. PbS CQDs were deposited uniformly by electrophoretic method on a TiO₂ photoelectrode applying 200 ​V for 60 ​min and used as photosensitizers in a TiO₂ solar cell. Their photovoltaic parameters were studied under 1 sun illumination. Remarkably, we obtain power conversion efficiencies similar to those found in TiO₂ sensitized solar cells made with high quality PbS CQDs synthesized by hot injection method.