Co-sputtered Cu–Ag-based ZnO–Cu(Ag)–ZnO film enabling efficient flexible CuZnSnS solar cells with desirable mechanical endurance

To further enhance the mechanical endurance of ZnO–Cu–ZnO (ZCZ) films and CuZnSnS (CZTS) solar cells with deposited ZCZ films (ZCZ CSCs), Ag elements were introduced into metallic layers of ZCZ films using magnetron sputtering Cu–Ag co-sputtering techniques. The Ag addition effectively reduced the stresses generated during the growth of the Cu film, resulting in the suppression of three-dimensional island growth and the formation of a more uniform metallic film. Specifically, ZnO–Cu/Ag(35 W)–ZnO (ZCA35Z) films exhibited an average transmittance (T-ave) of 89%, outperforming the ZCZ film with a T-ave of 80%, achieved by increasing the continuity of metallic layers. Moreover, ZCA35Z CSCs demonstrated a higher power conversion efficiency (PCE) value of 6.38% compared to ZCZ CSCs (6.01%) without bending. Additionally, the PCE value of ZCA35Z CSCs showed a 9% improvement over ZCZ CSCs at a bending diameter of 10 mm. Remarkably, even after 1000 bending cycles, the PCE value of ZCA35Z CSCs exhibited a substantial 15% enhancement compared to ZCZ CSCs, which can be attributed to the continuous Cu films enhancing carrier migration and reducing optical losses. This new method to enhance the mechanical endurance of ZCZ films and ZCZ CSCs by increasing Cu film continuity via Cu–Ag co-sputtering presents a promising approach to boost the performance of flexible electronics.