Effect of Rapid Thermal Processing on the structural and device properties of (Ag,Cu)(In,Ga)Se2 thin film solar cells

Abstract (Ag w Cu 1 − w )(In 1 − x Ga x )Se 2 alloy absorber layers with w ≈ 0.8 and x ≈ 0.78 ratios were deposited using multi-source elemental evaporation and analyzed by glancing incidence X-ray diffraction, scanning electron microscopy combined with energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The effect of Rapid Thermal Processing (RTP) on the structure and composition of the near-surface layers was investigated. It was found that the RTP doesn't have a noticeable effect on the grain size and roughness of the film surface. On the other hand, additional reflections of the films with 0.5 ≤ Ga/(Ga + In)   0.5, due to an ordered defect phase which is confined to the near-surface region of the film, are completely diminished after RTP with excess Se present. X-ray photoelectron spectroscopy results show that RTP with excess Se present altered the distribution of elements, rendering the film surface less group I deficient after that process. Consequently, atomic ratios were changed from the composition of I 1 III 5 VI 8 compound to the composition close to that of I 1 III 3 VI 5 ordered defect phase. Additionally, the RTP treatment, especially with excess Se, significantly enhanced solar cell efficiency performance due to an improvement in the open circuit voltage.