The influence of Se beam pressure on defect properties in Cu(In(1-x),Ga(x))Se(2) (CIGS)-based solar cells fabricated by the three-stage process was investigated by admittance spectroscopy. The Se beam pressure was varied from 1.3 x 10(-3) to 4.4 x 10(-3) Pa, at the position of the samples, by varying the Se cell temperature. The spectra for all samples show three distinct peaks denoted as alpha, beta, and zeta with activation energies of 20, 150, and 300 meV, respectively. The trap density of C increased from 5 x 10(14) to 4 x 10(15) cm(-3) with decrease in Se beam pressure; the trap densities of alpha and beta did not change. These results suggest that the origin of zeta is related to the Se deficiency. The density of zeta seems to correlate with the cell efficiency. Therefore, it is important to control the Se beam pressure in order to obtain highly efficient solar cells. (C) 2010 Elsevier B.V. All rights reserved.