Incongruent reaction of Cu–(InGa) intermetallic precursors in H2Se and H2S

Publisher Website
Google Scholar
Abstract
The reaction pathways to form Cu ( In Ga ) Se 2 or Cu ( In Ga ) S 2 films at 450 ° C from metallic precursors were evaluated by reacting Cu–In–Ga films in H 2 Se or H 2 S for 10, 30, or 90 min and characterizing the phase composition of the resulting films. A starting composition comprising Cu 9 ( In 0.64 Ga 0.36 ) 4 and In phases was detected by x-ray diffraction in Cu–Ga–In precursors annealed at 450 ° C in an Ar atmosphere. When the precursors were reacted in H 2 Se , a graded Cu ( In Ga ) Se 2 film was formed with a Ga-rich composition and residual Cu–Ga intermetallics at the interface with the Mo back contact. The intermetallic compounds were observed to evolve from Cu 9 ( In 0.64 Ga 0.36 ) 4 to Cu 9 Ga 4 with increasing selenization time. Reaction in H 2 S formed inhomogeneous Cu ( In Ga ) S 2 with Cu–In intermetallics. The results are consistent with thermochemical predictions of the preferential reaction of In with Se, and Ga with S. These reaction preferences can explain the formation of a graded Cu ( In Ga ) Se 2 film during reaction in H 2 Se and provide a refined understanding of the reaction sequence in two-step H 2 Se ∕ H 2 S processes.