In article number 1803476, by Sang Il Seok and co-workers, the stability of the perovskite precursor solution and the resulting perovskite thin layer is significantly improved by adding a certain amount of sulfur to the precursor solution. It is found that the sulfur coordinates with the methylammonium cations in the precursor solution to inhibit de-protonation and increase the chemical binding energy due to the interstitial sulfur ions in the perovskite lattice.