Phase development, microstructure and optical properties of Cu2ZnSnSe4 thin films modified with Pb and Ti

► First report of Pb and Ti substitutions in Cu2ZnSnSe4 thin films ► Substitution of Pb for the Cu site and Ti for the Sn site ► Phase evolution: precipitation of secondary phases with increasing Pb or Ti ► Pb for grain growth and Ti for growth inhibition at initial substitutions ► Band gap control by the substitution of Pb and Ti up to 2.1 eV