- Chemical bath deposition is an effective method for depositing semiconductor thin films with a wide range of compositions and microstructures. While it is widely accepted that organic additive molecules can play a very important role in chemical bath deposition, their role has not been systematically studied. In the present work, we have comparatively studied the effect of four common water-soluble molecules, 1, 2-ethanedithiol, mercaptopropionic acid, cysteamine and mercaptoethanol, on the chemical bath deposition of lead sulfide. The effect of 1, 2-ethanedithiol was shown to be markedly different, resulting in a significantly increased film thickness. We show the effect of each additive on the growth rate, microstructure and optical properties, and provide insights on their mechanism of operation.