High Efficiency CIGS Solar Cells by Bulk Defect Passivation through Ag Substituting Strategy

Cu(In,Ga)Se₂ (CIGS) is considered a promising photovoltaics material due to its excellent properties and high efficiency. However, the complicated deep defects (such as In_Cu or Ga_Cu) in the CIGS layer hamper the development of polycrystalline CIGS solar cells. Numerous efforts have been employed to passivate these defects which distributed in the grain boundary and the CIGS/CdS interface. In this work, we implemented an effective Ag substituting approach to passivate bulk defects in CIGS absorber. The composition and phase characterizations revealed that Ag was successfully incorporated in the CIGS lattice. The substituting of Ag could boost the crystallization without obviously changing the band gap. The C-V and EIS results demonstrated that the device showed enlarged W_d and beneficial carrier transport dynamics after Ag incorporation. The DLTS result revealed that the deep In_Cu defect density was dramatically decreased after Ag substituting for Cu. A champion Ag-substituted CIGS device exhibited a remarkable efficiency of 15.82%, with improved V_OC of 630 mV, J_SC of 34.44 mA/cm², and FF of 72.90%. Comparing with the efficiency of an unsubstituted CIGS device (12.18%), a Ag-substituted CIGS device exhibited 30% enhancement.