Jsc improvement of CdS/Cu(In,Ga)Se2 solar cells after rapid thermal annealing

The thermal dynamic influence of microstructure and physical phase leading to the variation on the short-circuit density (J_sc) for the large size of CIGS solar cell has been investigated by the subsequent rapid thermal annealing (RTA) and optical and electrical analyses, respectively. The annealing temperature of 300°C is an optimized point for a high efficiency of 11.75% to a 125 × 125 mm² cell. The photoluminescence (PL) and Raman spectra are used to electrical analysis on the improvement of J_sc. After RTA at 300°C treatment, the PL intensity increase about 15 times accompany with the vanish of deep level centers or traps such as vacancies and interstitials. The feature of the intensity and FWHM of Raman peak A₁ is related to the grain sizes. The results indicate that subsequent thermal treatment of CIGS device directly leads to the reduction of deep levels and an increase of the concentration of minor carriers. The observation from the front reflection spectrum (FRS) and atomic force microscope (AFM) indicates that the increase of surface roughness causes the decrease of front reflection. It is obvious that the enhancement of J_sc can be ascribed to the less optical losses on the surface reflection and the increase of the diffusion current in the bulk.