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

In this paper, we investigated the effect of rapid thermal annealing (RTA) on solar cell performance. An opto-electric conversion efficiency of 11.75% (V_oc= 0.64 V, J_sc= 25.88 mA/cm², FF=72.08%) was obtained under AM 1.5G when the cell was annealed at 300 ℃ for 30 s. The annealed solar cell showed an average absolute efficiency 1.5% higher than that of the as-deposited one. For the microstructure analysis and the physical phase confirmation, X-ray diffraction (XRD), Raman spectra, front surface reflection (FSR), internal quantum efficiency (IQE), and X-ray photoelectron spectroscopy (XPS) were respectively applied to distinguish the causes inducing the efficiency variation. All experimental results implied that the RTA eliminated recombination centers at the p-n junction, reduced the surface optical losses, enhanced the blue response of the CdS buffer layer, and improved the ohmic contact between Mo and Cu(In, Ga)Se₂ (CIGS) layers. This leaded to the improved performance of CIGS solar cell.