Improved CuGaSe2 absorber properties through a modified co-evaporation process

•Regular CuPRO process leads to an inhomogeneous CuGaSe2 (CGSe) layer.•Applying relaxation stages during the growth yields to a homogeneous absorber.•The relaxation stages improve the solar cell performance.•Raman analysis can be used to study chemical variations throughout the CGSe film. The present study deals with CuGaSe2-thin-films for solar cell applications. With the aim of achieving chemically and structurally homogeneous CuGaSe2 layers, it is proposed a modified co-evaporation process, which implies two so-called relaxation sequences during films growth. The resulting layers are characterized by scanning electron microscopy and Raman spectroscopy. By comparing their characteristics with those of CuGaSe2 grown without relaxation sequence, it is demonstrated that the modified process yields improved distribution of elements throughout the whole layer. The performance of the resulting solar cells is improved exclusively through increased quantum efficiency in the large wavelengths; further output voltage increase would require alternative junction partners.