However, band-gap of the CIGS absorber layer affects the
fill-factor of the cell. As the band-gap increased beyond 1.3eV,
fill factor decreased sharply. Because increased Ga content
causes higher recombination rate and lower carrier lifetime, for
which recombination in SCR may overweight the
recombination outside of this region. So, ideality factor in
accordance with the FF will be decreased due to defect in SCR.
This is a key parameter in evaluating solar cell performance.
Solar cell with a high fill factor is very desirable, because small
amount of the current is dissipated by internal losses [13].
The trade of among these phenomena is that, an optimum
band-gap of 1.3eV is proposed in which the device have a high
fill factor without sacrificing its Voc or lsc. The result yields a
maximum efficiency of 22.18%.