Characteristics of Cu(In, Ga)Se2 thin films grown by co-evaporation using a fluxmeter

Cu(In,Ga)Se-2 (CIGS) thin-film solar cells has best efficiency above 19.9% among thin-film solar cells, and have potential applications in a broad range of technologies. The structure of CIGS solar cells consists of five unit layers, including a back contact, a light-absorption layer (absorber), a buffer, a front transparent conducting electrode, and an antireflection layer, formed sequentially. Materials and thin-film units of various compositions are manufactured by a variety of methods; physical and chemical methods are used to prepare thin-film CIGS solar cells. Because it is difficult to control the composition of the CIGS absorber layer, in this study, the vapor pressures were measured and controlled using a vapor fluxmeter. The vapor pressures of Cu, In, Ga, and Se were similar to 2.8x10(-5) to 4.0x10(-5), similar to 1.1x10(-4) to 1.3x10(-4), similar to 1.9x10(-5) to 3.7x10(-5), and similar to 2.8x10(-4) to 4.3x10(-4) Pa, respectively. The characteristics of CIGS thin films were investigated using X-ray diffraction (XRD), scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS), and photoluminescence (PL) spectroscopy using a helium-neon (HeNe) laser. The temperature dependencies of the PL spectra were measured at a wavelength of 1137 nm. XRD patterns showed several intense peaks at (101), (112), (220)/(204), and (312)/(116), indicating the chalcopyrite structure of CIGS.