Optimization of buffer layer/i-layer band alignment

We investigate how conduction band offset between the buffer and the i-layer of Cu(InGa)Se₂ solar cells affects their performance. Employing SCAPS simulations, we explore two specific cases with either a CdS buffer or an alternative Zn(OS) buffer of a higher conduction band energy. These studies are supported by experimental results using (ZnMg)O as a model i-layer material. We find that pure ZnO is the suitable i-layer for chalcogenide-based solar cells only if combined with the CdS buffer. However, another i-layer material with a higher conduction band edge is needed if CdS is replaced by an alternative buffer of a wider band gap, such as Zn(OS).