| AVS 63rd International Symposium & Exhibition | |
| Thin Film | Thursday Sessions |
| Session TF-ThP |
| Session: | Thin Films Poster Session |
| Presenter: | Kevin Jones, University of Delaware |
| Authors: | K. Jones, University of Delaware R.L. Opila, University of Delaware F. Fang, University of Delaware L. Chen, University of Delaware and Institute of Energy Conversion at University of Delaware W. Shafaraman, University of Delaware and Institute of Energy Conversion at University of Delaware |
| Correspondent: | Click to Email |
The surface valence band-edge energy lies below the Fermi level by about 1.1eV for CuInSe2. This energy is larger than the bulk band gap energy of 1.04eV, therefore was indicated that the surface of CuInSe2 has a wider bandgap than its bulk. It was later found that the surface band gap of polycrystalline CuInSe2 is 1.4eV, more than 0.3eV larger than its bulk band gap. This led to many experimental observations of what may be the cause of this surface widening effect, in which most progress has been computational. Empirical data suggest that preferential formations of electrical neutral defect pairs are created naturally in Cu-chalcopyrites, in which forms a so called “surface defect layer” on the surface and between the interfaces of the buffer and back contact layer of Cu-based solar devices. The need for an efficient wide band gap absorber has been established for a monolithic tandem solar cell design of the Cu(In,Ga)Se2 thin-film system, therefore, understanding related surface electronic properties is a necessity for band gap tuning. This work investigates the surfaces of the proposed Ag-alloyed wide band gap system of Cu(In,Ga)Se2, by way of ultra-violet photoemission spectroscopy. In these efforts, we relate the valence band spectra of certain Ag and Ga ratios of Cu-In-Se system to reported empirical data of CuInSe2 and CuIn5Se8 (ODC) stoichiometry, and how these ratios effect surface electronic properties.