| AVS 56th International Symposium & Exhibition | |
| Thin Film | Monday Sessions |
| Session TF1+PV-MoA |
| Session: | Chalcogenide Photovoltaics |
| Presenter: | T.C. Kaspar, Pacific Northwest National Laboratory |
| Authors: | T.C. Kaspar, Pacific Northwest National Laboratory T. Droubay, Pacific Northwest National Laboratory J.E. Jaffe, Pacific Northwest National Laboratory V. Shutthanandan, Pacific Northwest National Laboratory W. Jiang, Pacific Northwest National Laboratory S.A. Chambers, Pacific Northwest National Laboratory G.J. Exarhos, Pacific Northwest National Laboratory |
| Correspondent: | Click to Email |
All photovoltaic devices require efficient electron-hole separation, transport, and collection. It is relatively straightforward to experimentally determine the charge transport properties of the individual component materials in a given cell design, allowing optimization. However, the charge transport across heterojunction interfaces between component materials is just as critical for overall cell performance. The electron or hole injection efficiency is determined by the band structure alignment at the interface; optimization of the interface for facile charge injection requires detailed knowledge of the band offsets, which cannot easily be determined by electrical transport measurements. We utilize high resolution x-ray photoelectron spectroscopy (XPS) to directly quantify the band offsets of heterojunctions relevant to photovoltaic cells. Nanostructured extremely thin absorber (ETA) photovoltaic devices have been proposed as an inexpensive alternative to current single-crystal device technology, although the devices reported thus far suffer from low conversion efficiency. Thus, materials relevant to ETA devices were chosen for study: n-ZnO as the electron transporter, solid-state p-CuSCN as the hole conductor, and CdTe as the photon absorber. High quality ZnO thin films were deposited by pulsed laser deposition (PLD) on F:SnO2/glass substrates for XPS band offset measurements. The band offsets were determined as a function of ZnO conductivity, and strategies for improved electron conduction across the interface will be discussed. In addition, the materials properties of CuSCN were thoroughly characterized, and its electronic structure was compared to density functional theory (DFT) calculations. The calculations show an indirect bandgap of 2.7eV and highly anisotropic charge transport with the unusual prediction that hole mobility exceeds the electron mobility. Avenues to improve hole conduction through the introduction of defects in CuSCN were explored.