| AVS 61st International Symposium & Exhibition | |
| Energy Frontiers Focus Topic | Wednesday Sessions |
| Session EN+AS+EM+SE-WeM |
| Session: | Thin Film Photovoltaics |
| Presenter: | Angus Rockett, University of Illinois at Urbana Champaign |
| Authors: | X. He, University of Illinois at Urbana Champaign H. Tellez, Kyushu University, Japan J. Druce, Kyushu University, Japan K. Demirkan, Miasole P. Ercius, Lawrence Berkeley National Laboratory V. Lordi, Lawrence Livermore National Laboratory J. Kilner, Imperial College London, UK T. Ishihara, Kyushu University, Japan A. Rockett, University of Illinois at Urbana Champaign |
| Correspondent: | Click to Email |
Cu(In,Ga)Se2 (CIGS) photovoltaics are very promising candidates for high-performance energy generation from sunlight. They typically include a heterojunction between CdS and CIGS. The nature of that heterojunction is critical to the performance of the devices. We present experimental results on the nanochemistry of CIGS and CIGS/CdS heterojunctions and the nanostructure of the junctions. In particular we present low energy ion scattering (LEIS) results on epitaxial single crystal CIGS and CIGS/CdS heterojunctions formed by chemical bath deposition of CdS. Also shown are results of high-resolution transmission electron microscopy (TEM) studies of the CIGS/CdS heterojunction where the junction is formed by physical vapor deposition. LEIS has single-atomic-layer chemical sensitivity that provides a unique ability to distinguish the nanochemical nature of CIGS surfaces and heterojunctions. TEM provides both nanostructural information and the possibility to determine the chemistry of the junction on the nanoscale by energy dispersive spectroscopy and energy filtered imaging. Complete epitaxy of the CdS throughout its ~50 nm thickness is observed in the physical-vapor-deposited CdS. Domains of cubic zincblende and hexagonal wurtzite structure CdS have been observed. Twins in the CIGS grains were found to propagate into and often through the CdS layer, resulting in a twin or grain boundary in the CdS. The CdS epitaxial relationship and the effect of surface steps on the CIGS surface are shown. The nanochemical analysis results show significant penetration of Cu into the CdS layer, although no alteration in the CdS nanostructure is observed. The other elements show an abrupt nanochemical junction. LEIS results show the presence of segregated layers on the CIGS surface and further refine the nature of the nanochemical intermixing across the interface.