Design, photoelectric properties and electron transition mechanism of Cr doped p-CuGaS2 compound based on intermediate band effect

Abstract The p-CuGaS2 and Cr doped p-CuGaS2 compounds are first fabricated by the solvothermal method using CuI, C12H26S, C15H21GaO6, and C15H21CrO6 as starting materials. The Cr3+ is successfully doped into the CuGaS2 compounds with a single chalcopyrite structure and partially replaced Ga3+. The two additional sub-bandgap optical absorption edges (‘B’ and ‘C’) are observed in the UV–Vis–NIR absorption spectra of the sample with a Cr doping content of 0.99%. ‘C’ and ‘B’ correspond to the absorption extra photons of hν1 (valence band maxima intermediate band, 0.8 eV) and hν2 (intermediate band conduction band minimum, 1.2 eV), which proves the formation of the intermediate band in the Cr doped CuGaS2. The Hall effect measurement shows that the resistivity of Cr doped CuGaS2 compound decreases with the increase of Cr doping content, while the carrier concentration and mobility are increased. The half-filled state of intermediate band is confirmed according to Fermi level tested by the ultraviolet photoelectron spectroscopy. The photocurrent responses analysis suggests that the intermediate band leads to the increase of photo-induced carriers. The band structure and electron transition mechanism of Cr doped CuGaS2 compounds are discussed in details.