In this study, a uniform and dense cadmium sulfide (CdS) thin film is utilised as an electron-transport layer in CH₃NH₃PbI₃-based perovskite solar cells (PSCs). CdS films are synthesized by a homogeneous precipitation method in urea aqueous solution. The effect of urea concentration on the growth of CdS films has been investigated. It is noted that increasing urea concentration remarkably affects the grain size and uniformity of the films. A compact CdS thin film with appropriate grain size can be obtained by adding 1.5 M urea. The photovoltaic performance of the PSCs based on the as-prepared CdS films is also studied. The photovoltaic conversion efficiency (PCE) of the PSCs shows a significant dependence on CdS layers. The highest PCE is obtained by using a CdS thin film prepared in 1.5 M urea, which can be attributed to the better coverage of perovskite on the CdS film for efficient charge separation and transport.