Fig. 1. Sketch diagram of the absorber layer deposition process. The PRE-Ag process is referring to the Ag–Se precursor deposition process, which was prepared before the CIGS deposition process. In addition, the Ag surface treatment process carried out on the surface of CIGS films is denoted as the PDT-Ag process.

Fig. 2. (a) XRD patterns of the CIGS films with Ag. (b) The corresponding grazing incident X-ray diffraction (GIXRD) patterns of absorber layers.

Fig. 3. Cross-sectional SEM images of CIGS films of (a) A, (b) B, and (c) C.

Fig. 4. (a) J-V curves of the best CIGS solar cells fabricated from the different absorber samples. Statistic boxes for the (b) V_OC, (c) J_SC, and (d) FF and each box contains over 10 solar cells.

Fig. 5. (a) External quantum efficiency (EQE) spectrum. (b) The band gap value obtained by EQE fitting curve. (c) Doping concentration (N_a) of different samples. (d) ln(EQE) as a function of photon energy to determine the Urbach energy (E_U) values.

Fig. 6. Charge barrier height Φ_b of different samples.