Improvement of Ga distribution and enhancement of grain growth of CuInGaSe2 by incorporating a thin CuGa layer on the single CuInGa precursor

► A thin CuGa layer is deposited on the single CuInGa ternary precursor. ► The CuGa layer can enhance the grain growth and increase Ga concentration of CuInGaSe2. ► Increasing Ga concentration can enhance the open circuit voltage (Voc) of CIGS device. ► The Voc and efficiency of the device were increased by about 15% and 27%, respectively.