A study on composition, structure and optical properties of copper-poor CIGS thin film deposited by sequential sputtering of CuGa/In and In/(CuGa+In) precursors

Copper-poor CIGS thin films were fabricated by using two precursor of CuGa/In and In/(CuGa+In) onto the Mo coated soda-lime glass (SLG) by the sequential sputtering of CuGa and In targets. The CIG precursors were converted into CIGS absorption thin film by selenization process. The X-ray diffraction (XRD) patterns of CIGS absorber from CuGa/In precursor exhibits strong (112) preferred orientation that is more stable than (220)/(204) as compared to In/(CuGa+In) precursor. The elemental composition uniformity onto the surface and along depth were extensively analyzed with energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). For as-fabricated CIGS thin films from In/(CuGa+In) and CuGa/In precursors, the atomic (at%) composition values of [Cu]//[In+Ga]/=1.14, 1.08 and [Ga]/[In+Ga]=0.33, 0.20 were observed, respectively that is well matched for highest efficient CIGS-based solar cell so far. SIMS confirmed that the Ga profile is not through the depth of CIGS thin film attributed a consistent band gap of 1.04 and 1.08 eV. Further, PL spectrum of CIGS absorber formed by CuGa/In precursor exhibits relatively narrow emission peak as compared to In/(CuGa+In) precursor. It is attributed to decrease defect density with uniform composition in the CIGS absorber. The carrier concentration (Np) found to increase from 1020 to 1021 cm−3 orders with the increase of Cu/(In+Ga) at.% from 0.93 to 1.02, which is related to the increasing carrier concentration for stoichiometric CIGS films.

► High quality, controlled band gap, Cu-poor CIGS films were fabricated by sputtering.
► The at% of [Cu]/[In+Ga] and [Ga]/[In+Ga] matched with highest efficient solar cell.
► From SIMS, Ga profile is not through the CIGS that attributes consistent band gap.
► Optical properties of CIGS film confirmed the composition of Cu-poor layer.