Optical properties and electronic structures of CuSbS 2 , CuSbSe 2 , and CuSb(S 1−x Se x ) 2 solid solution

Abstract

To clarify electronic structures of CuSbS2, CuSbSe2, and CuSb(S1−xSex)2 solid solutions, these powder samples were synthesized by a mechanochemical process and post-heating. CuSbS2 and CuSbSe2 have indirect and direct band gaps, of which the direct band gaps are a little wider than the indirect band gaps. The ionization energies of CuSb(S1−xSex)2 (0.0 ≤ x ≤ 1.0) powders were measured by photoemission yield spectroscopy (PYS). Energy levels of the valence band maximum (VBM) of the CuSb(S1−xSex)2 samples were estimated from the ionization energies. The electron affinity, energy level of conduction band minimum (CBM), of the CuSb(S1−xSex)2 samples could also be determined by adding the value of the optical band gap to the energy level of the VBM. The energy level of the VBM of the CuSb(S1−xSex)2 system monotonically increases from −5.45 eV for CuSbS2 (x = 0.0) to −5.15 eV for CuSbSe2 (x = 1.0). On the other hand, the energy levels of the indirect CBM of the CuSb(S1−xSex)2 system slightly decrease from −4.05 eV for CuSbS2 to −4.11 eV for CuSbSe2. The energy levels of the direct CBM also slightly decrease from −4.00 eV for CuSbS2 to −4.07 eV for CuSbSe2. We show the band alignment of CuSbS2 (CuSbSe2)-based solar cells with a standard device structure of ZnO/CdS/CuSbS2 (CuSbSe2) absorber.