ZnGeAs2: A Novel Semiconductor for Photovoltaics – Tim Peshek
Date: Mon. January 4th, 2010, 12:30 pm-1:30 pmLocation: Rockefeller 221
> I will motivate the fabrication of tandem thin film devices based solely on II-IV-V2 compounds as a target for wide-scale PV deployment. Third generation solar cells must overcome the Shockley-Queisser (SQ) limitation of single diode solar cells; the fabrication of multiple junction solar cells is one avenue to circumvent the SQ limit. Currently, the high cost of highly efficient multiple junction cells (e.g. the >40% efficient Ge/GaAs/InGaP triple junction) prohibits these devices from being widely deployed in the market. The challenge to condensed matter physics is to identify semiconductors that have optimal properties for multi-junction cells, including material abundance and low manufacturing costs. ZnGeAs2 is an attractive candidate because it has a direct 1.10 eV band gap. Additionally, ZnGeAs2 is the II-IV-V2 analogue of GaAs, so its lattice constants are matched to GaAs. II-IV-V2 compounds in general are attractive because they are a family of tetrahedrally bound compounds that form very strong unidirectional bonds, which typically have high defect formation energies and strong optical absorption. Additionally, candidates from this family are often composed of abundant and inexpensive elements, e.g. Zn, Sn, Ge, P, etc. I will present results of a detailed study of this compound including measurements of ideal growth conditions, thermodynamic stability, and device results for the first solar cells ever fabricated using ZnGeAs2 as an absorber layer.