As part of the process in manufacturing Cu 2 ZnSiSe 4 , films of Cu 2 SiSe 3 were synthesized and a bandgap of 1.4 eV determined using transmission measurements in 2015. These measurements give an indication of the Cu 2 SiSe 3 bandgap, however the sample contained significant amounts of secondary phases and the synthesis process was not refined for high-quality films.