ABSTRACT
Cu(In,Ga)Se2 thin films have been prepared by thermal crystallization of evaporated amorphous-like precursor with Ga/(In+Ga)=0.6 using two kinds of heating processes: precursors were annealed from room temperature to 550°C at a constant heating rate (1 step growth), and another ones were annealed at different heating rates between room temperature-200°C and 200°C–550°C (2 step growth). Thin films crystallized below the heating rate of 1°C/min in the 1 step growth and at 1°C/min in the first stage of the 2 step growth, independent of the heating rate in the second stage, were nearly stoichiometric and had a single phase Cu(In,Ga)Se2 with chalcopyrite structure. On the other hand, Cu(In,Ga)Se2 and Cu-Se binary compound coexisted in the thin films crystallized under other conditions. In the 2 step growth, the grain sizes in Cu(In,Ga)Se2 thin films prepared at l°C/min in the first stage increased remarkably with increasing the heating rate in the second stage. The optical transition for Cu(In,Ga)Se2 thin films crystallized at 1°C/min in the first stage of the 2 step growth was very sharp, and the band gap was estimated at 1.35 eV close to the optimum range for solar energy conversion.
