An efficiency of over 18% have been achieved in Cu(In,Ga)Se, (CIGS) thin-fi
lm solar cells. Solar cell parameters were estimated for the cells with eff
iciencies of more and less than 18%. A diode quality factor n and forward c
urrent (saturated current) J(0) of the cell with over 18% efficiency are lo
wer than those with below 18% efficiency. This would be attributed to suffi
cient coverage of the CdS film with excellent uniformity as a buffer and/or
window layer over the CIGS film because the process of CdS film formation
was improved. (C) 2001 Elsevier Science B.V. All rights reserved.