Influence of Cu content on the physical characteristics of CuxGaCr0.1S2 thin films for intermediate band solar cells

Abstract

Intermediate band semiconductors can increase the efficiency of photovoltaic solar cells via sequential absorption of photons in a wider range of the solar spectrum. The introduction of Cr substituting Ga atoms in the chalcopyrite CuGaS2 is proposed to create a suitable intermediate band, investigating the influence of the Cu/Ga ratio on the structural, morphological, optical, and electrical characteristics. For this purpose, CuxGaS2 and CuxGaCr0.1S2 thin films (with x ranging from 0.8 to 1.2) are prepared by modulated evaporation from elemental sources and analyzed comparatively by X-ray diffraction, Raman spectroscopy, atomic force microscopy, spectrophotometry, and Hall effect measurements. The incorporation of Cr produces an in-gap absorption that is independent of the Cu/Ga ratio. The mean crystallite size, surface roughness, and electrical conductivity increase with the Cu content in both CuxGaS2 and CuxGaCr0.1S2.