Study on the Performance of Oxygen-Rich Zn(O,S) Buffers Fabricated by Sputtering Deposition and Zn(O,S)/Cu(In,Ga)(S,Se)2 Interfaces

We developed a novel process for fabricating oxygen-rich Zn­(O,S) buffer layers by magnetron reactive sputtering with a single oxygen-rich Zn­(O,S) target, suitable for industrial all-dry production. Then, we successfully fabricated Cd-free Cu­(In,Ga)­(S,Se)2 (CIGSSe) solar cells. By varying the oxygen partial pressure during sputtering from 0 to 20%, we precisely controlled the Zn­(O,S) composition, then systematically investigated its effects on the quality of oxygen-rich Zn­(O,S) films, the properties of formed p–n junctions, and the performance of CIGSSe solar cells with Zn­(O,S) buffer. We demonstrated that reactive sputtering with a Zn­(O,S) target can generate a homogeneous, high-quality oxygen-rich Zn­(O,S) buffer on large-area substrates. We observed a unique and unusual phenomenon: the appropriate content of secondary phase ZnSO4 and ZnSO3 improved the band alignment for oxygen-rich Zn­(O,S). Combining our proposed schematic diagram of band alignmentat the Zn­(O,S)/CIGSSe interface, we established a crucial correlation between the device performance and the interfacial properties at the p–n junction. For the CIGSSe device performance, the band alignment matching at the heterojunction plays a primary role, and the quality of oxygen-rich Zn­(O,S) films plays a secondary role. Consequently, an excellent oxygen-rich Zn­(O,S) buffer can be obtained with 10% Zn­(O,S) deposition oxygen partial pressure , and the optimized device shows a higher V oc (447 mV) and a similar conversion efficiency (11.2%) than conventional CIGSSe devices with CdS buffer.