Wide bandgap CIGS thin films via Ag-PDT to ameliorate the interface quality of CIGS/CdS heterojunction

Wide bandgap Cu(In,Ga)Se₂ (CIGS) thin films play an important role in tandem solar cells. However, the wide bandgap CIGS obtained by high gallium content is usually in accompany with fine grains and serious interface problems, which leads to the degradation of device performance. In this work, we adopt silver post-deposition treatment (Ag-PDT) to reduce the interface recombination of high gallium CIGS/CdS heterojunction [CIGS_Eg≈1.3 eV, ((Ga/(Ga + In), GGI) = 0.5], resulting in improved device performance. When Ag is introduced into CIGS film, it preferentially reacts with In to produce AgInSe₂ that enhances the surface layer crystallization of the absorber. Simultaneously, the reaction of Ag and Se produces liquid phase Ag₂Se in the deposition process, which can smoothen the surface roughness of high-gallium CIGS absorber. Nevertheless, excessive Ag₂Se accumulation on the surface of absorber brings severe interface recombination in the heterojunction, generating higher current leakage. Finally, after optimization, the device with power conversion efficiency (PCE) of 17.8% (without anti-reflecting layer) was obtained in the process of Ag-PDT. For the further development of wide bandgap CIGS thin film solar cells with high performance, silver post-deposition treatment is validated as a simple optimization way of heterojunction interface.