Improvement of bandgap homogeneity in Cu(In,Ga)Se2 thin films using a modified two-step selenization process

A modified two-step selenization has been demonstrated to overcome inhomogeneous gallium distribution, an issue to lower energy bandgap in the space-charge region as well as cell efficiency. It was found that incorporating selenium into conventional precursors could accelerate the formation of CuInGaSe2 phase in the selenization to accordingly suppress the diffusion effect of gallium. By introducing a pre-heating treatment, this selenization enhanced the bandgap distribution with a back-surface field and an increase of bandgap in the space-charge region, consequently improving open circuit voltage (V-OC) by 25% and cell efficiency by 55%, respectively. (C) 2013 AIP Publishing LLC.