The growth of grain size of CuInGaSe2 and the Ga distribution in the thin film CuInGaSe2 solar cell devices fabricated using a sputtering CuInGa ternary target have been studied. It was observed, adding a thin CuGa layer on top of the surface of CuInGa ternary precursor would increase the Ga concentration, and thus the energy gap in the space-charge region after selenization. As a result, the open circuit voltage (V-OC) of the device was increased by 15%. The SEM and XRD studies further show that the addition of a CuGa layer enhanced the growth of grain size of CuInGaSe2 during selenization and increased the conversion efficiency of the solar cell devices by 27% (from 6.3% to 8%). (C) 2011 Elsevier Ltd. All rights reserved.