Effects of cooling rate and post-heat treatment on properties of ZnO thin films deposited by sol-gel method

► Deposition of precursor solution on Si substrate for the growth of ZnO thin films by sol-gel spin-coating method. ► The solution was cooled with different rates after pre-heat treatment. ► The surface morphology, the residual stress, and the optical properties are affected by the cooling rate. ► The rapid cooling is more suitable than the slow cooling.