Interface Analysis of Cu(In,Ga)Se2 and ZnS Formed Using Sulfur Thermal Cracker

We analyzed the interface characteristics of Zn‐based thin‐film buffer layers formed by a sulfur thermal cracker on a Cu(In,Ga)Se₂ (CIGS) light‐absorber layer. The analyzed Zn‐based thin‐film buffer layers are processed by a proposed method comprising two processes — Zn‐sputtering and cracker‐sulfurization. The processed buffer layers are then suitable to be used in the fabrication of highly efficient CIGS solar cells. Among the various Zn‐based film thicknesses, an 8 nm–thick Zn‐based film shows the highest power conversion efficiency for a solar cell. The band alignment of the buffer/CIGS was investigated by measuring the band‐gap energies and valence band levels across the depth direction. The conduction band difference between the near surface and interface in the buffer layer enables an efficient electron transport across the junction. We found the origin of the energy band structure by observing the chemical states. The fabricated buffer/CIGS layers have a structurally and chemically distinct interface with little elemental inter‐diffusion.