Defect levels and interface states in ZnO:B/buffer/Cu(In,Ga)(S,Se)(2)/Mo/glass solar cells with a Zn(S,O)/CdS, CdS, or Zn(S,O) buffer layer were investigated by capacitanceevoltage (C-V) and admittance spectroscopy. Two acceptor levels, A1 (with E-a,E-A1 = 0.09 +/- 0.01 eV activation energy) and A2 (E-a,E-A2 = 0.26 +/- 0.02 eV) were observed from the temperature dependence of the C-V profiles. Spatial distributions of these acceptors were determined by the bias dependence of the profiles. In addition, two kinds of defect signals, S1 (E-a,E-S1 = 0.06 eV and 0.07 eV) and S2 (E-a,E-S2 = 0.25 eV), were detected from admittance spectroscopy. Each solar cell exhibited only one signal: S1 in Zn(S,O)/CdS- or Zn(S,O)-buffered solar cells, and S2 in solar cell with a CdS buffer layer. These results demonstrate that buffer layers influence the spatial distributions of intrinsic defect states in the region of the Cu(In,Ga) (S,Se)(2) absorber close to the hetero-interface. (C) 2015 Elsevier B.V. All rights reserved.