Ga incorporation effects on the electronic structure of CuInS2:Na thin ®lms

Changes in the electronic structure of Na doped CuInS2 thin ®lms with Ga incorporation raising up the energy-conversion ef®ciency (Z) of n-CdS/p-CuInS2 solar cells from 10.6 to 11.2 were examined by ultraviolet±visible (UV±VIS) diffuse re¯ectance spectroscopy and X-ray photoelectron spectroscopy (XPS). The optical absorption energy of the CuInS2:Na ®lm increased from 1.40 to 1.43 eV with the Ga incorporation, though the valence band maximum (VBM) remained at constant. The enhanced open-circuit voltage (Voc) from 0.76 to 0.80 eV by the Ga incorporation can be ascribed to the observed widening of the optical band gap (Eg) by 0.03 eV. # 2001 Elsevier Science B.V. All rights reserved.