Fabrication of a smooth, large-grained Cu(In,Ga)Se2 thin film using a Cu/(In,Ga)2Se3 stacked precursor at low temperature for CIGS solar cells
Abstract
Cu(In,Ga)Se2 (CIGS) thin films used for commercial CIGS solar cells were fabricated from Cu–Ga–In metal precursors; they contained large voids at the CIGS/Mo interface and their surface was rather rough due to large volume expansion. To solve these problems, we employed a Cu/(In,Ga)2Se3 stacked precursor, in which the pre-existing Se could reduce the volume expansion during CIGS formation. With the pre-contained Se in the precursor, a uniform and void-free CIGS film with good adhesion was formed. SEM morphology revealed that a liquid phase was generated at 400 °C by the reaction of Cu and (In,Ga)2Se3 under Se deficient conditions even though the melting point of Cu and (In,Ga)2Se3 are much higher. A large-grained CIGS film can be formed as low as 450 °C with the help of liquid phase formation and we proposed the reaction mechanism. The film was applied to CIGS solar cells to achieve 13.5% efficiency without AR coating.
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