Effects of substrate temperature on the structural and electrical properties of Cu(In,Ga)Se2 thin films

Polycrystalline Cu(In,Ga)Se2 (CIGS) thin films were deposited onto soda-lime glass substrates using the three-stage process at the substrate temperature (Tsub) varying from 350 to 550 °C. The effect of Tsub on the structural and electrical properties of CIGS films has been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Hall effect measurement. We found that the surface roughness, constituent phases, film morphologies, resistivity (ρ) and carrier concentration (NP) of as-grown CIGS films indicated different change trends with increase in Tsub. The higher Tsub gives smooth surface, large grain size and single-phase CIGS films. The values of NP and ρ have two demarcated regions at Tsub of 380 and 450 °C. At lower Tsub of 380 °C, larger NP and lower ρ were dominated by the existence of secondary-phase CuxSe with lower resistivity. In the case of 450 °C, the obvious changes in NP and ρ can be attributed to the sufficient Na incorporation diffused from the glass substrate. Finally, the correlation of cell parameters with Tsub was analyzed.