STRUCTURE, CHEMISTRY, AND GROWTH MECHANISMS OF PHOTOVOLTAIC QUALITY THIN-FILM CU(IN,GA)SE-2 GROWN FROM A MIXED-PHASE PRECURSOR

The formation chemistry and growth dynamics of thin-film CuInSe2 grown by physical vapor deposition have been considered along the reaction path leading from the CuxSe:CuInSe2 two-phase region to single-phase CuInSe2. The (Cu2Se) β(CuInSe2)1-β (0<β≤1) mixed-phase precursor is created in a manner consistent with a liquid-phase assisted growth process. At substrate temperatures above 500°C and in the presence of excess Se, the film structure is columnar through the film thickness with column diameters in the range of 2.0-5.0 μm. Films deposited on glass are described as highly oriented with nearly exclusive (112) crystalline orientation. CuInSe2:CuxSe phase separation is identified and occurs primarily normal to the substrate plane at free surfaces. Single-phase CuInSe2 is created by the conversion of the Cu xSe into CuInSe2 upon exposure to In and Se activity. Noninterrupted columnar growth continues at substrate temperatures above 500°C. The addition of In in excess of that required for conversion produces an In-rich near-surface region with a CuIn3Se5 surface chemistry. A model is developed that describes the growth process. The model provides a vision for the production of thin-film CuInSe2 in industrial scale systems. Photovoltaic devices incorporating Ga with total-area efficiencies of 14.4%-16.4% have been produced by this process and variations on this process. © 1995 American Institute of Physics.