Preparation of device quality chalcopyrite thin films by thermal evaporation of compound materials

In this study, chalcopyrite thin films were prepared by the relatively slow thermal evaporation of compound chalcopyrite materials. The pulverized starting materials were heated from room temperature to a maximum temperature around 1400 degreesC over a period of 10 min. This growth sequence to a large degree prevented the generally reported problems associated with flash evaporation such as material spitting, inhomogeneous material properties and poor reproducibility. It was also possible to exercise accurate control over the composition of the final films by using predetermined masses of starting materials. Using this approach, it was possible to produce single-phase CuInSe2 thin films at substrate temperatures as low as 350 degreesC. In contrast, evaporation of CuGaSe2 or Cu(In,Ga)Se-2 compounds at low substrate temperatures resulted in final films characterized by the presence of several crystallographic phases. In the latter cases, single-phase material was only obtained after post-growth rapid thermal treatment at 550 degreesC for 6 min. Solar cell devices fabricated from CuInSe2 and Cu(In,Ga)Se-2 absorber films demonstrated favourable results.