Chalcopyrite thin films and solar cells prepared by using selenoamide as a selenium source

Abstract

CuInSe2 (CIS) and Cu(In,Ga)Se2 (CIGS) thin films were prepared by selenizing stacked Cu–In and In–CuGa metal layers, respectively, with selenoamide in a tube furnace at 400°C at atmospheric pressure for solar cell fabrication. Chalcogen amides can allow safe transportation and handling of chalcogen sources that can produce chalcogen hydrides at reasonably low temperature. Selenoamide used in this study is stable at room temperature and decomposes into H2Se below 150°C. Towards the bottom of the CIS thin films, In segregation was observed particularly during selenization and it was concluded to be due to diffusion of released liquid In towards the bottom of the films and upward diffusion of Cu driven by Cu2−xSe formation on the surface during the process. Homogenizing In in CIS thin films was realized by carrying out post-selenization annealing without the presence of Se at 500°C for various time periods. On the other hand, Ga accumulated to the bottom of the CIGS thin films upon selenization creating a bandgap profile, which benefits collection of the minority carriers. The post-selenization annealing applied to CIGS thin films favored further intermixing between In and Ga while some degree of the bandgap profile was preserved. Solar cells fabricated with a soda–lime glass/Mo/CIS/CdS/ZnO/ZnO:Ga/Al structure exhibited power conversion efficiencies up to 1.6% without any further optimization.