A solar cell based on Cu(In1-x,Ga-x)Se-2 (CIGS) with bandgap (E-g) of 1.5 eV is superior because of the low coefficient of power loss and resistive losses. CIGS thin-films with the E-g = 1.5 eV and Cu/(Ga + In) (CGI) ratios of 0.92, 0.84, and 0.78 were deposited in this study using single-stage process. Photovoltaic (PV) parameters of the solar cell ameliorated on raising CGI values from 0.78 to 0.84, but abruptly deteriorated on further increasing the CGI value to 0.92. The PV properties of CIGS solar cell with CGI = 0.92 were poor due to the high defect density and low shunt resistance. The optimal CGI range for making efficient wide gap CIGS solar cells through the single-stage process was found to be from -0.80 to 0.84. The best CIGS solar cell with CGI value of 0.84 exhibited the conversion efficiency of 11.00%. (C) 2016 Elsevier B.V. All rights reserved.