Thermal Effect on the Electronic Properties of ZnO/CdS/CIGSeS Solar Cell at/near the Heterojunction Interfaces

Hard X-ray photoelectron spectroscopy (HAXPES) was utilized to investigate the thermal effect on heterojunction interfaces of a commercial CIGSeS-based solar cell, especially for the variations in its electronic properties and diffusion behaviors of the elements. To obtain depth-dependent information near the ZnO/CdS/CIGSeS heterojunction interfaces using a nondestructive method, we deliberately prepared a series of CIGSeS solar cells annealed at different temperatures with wedge-like ZnO window layers from a chemical etching method and collected the photoelectrons emitted from the samples with a lateral scan. A quantitative analysis of the HAXPES results revealed that all elements were upwardly diffused, whereas the cadmium atoms in the CdS buffer layer remained unchanged after the thermal treatment. Thermal annealing resulted in the disappearance of the ordered defect compound (ODC) domain and the band realignment at the ZnO/CdS/CIGSeS interfaces due to elemental interdiffusion. Our results elucidate the dominant mechanism behind the heat-induced degradation of the efficiency of energy conversion.