The authors studied the influence of sputtering a ZnMgO window layer for Cu (In,Ga) Se2 solar cells on bulk and interface electrical properties. Admittance spectroscopy reveals deep levels at the ZnMgO/CdS interface whose activation energy (∼0.4 eV) increases with reverse bias, indicating an unpinned quasi-Fermi level at the interface. The Cu (In,Ga) Se2 carrier concentration determined by capacitance-voltage measurements decreases to 3× 1014 cm-3 , compared to 1× 10 16 cm-3 in a device with a ZnO window. Scanning Kelvin probe force microscopy verifies the increased depletion region width and indicates that the junction location is unaltered by ZnMgO. Secondary-ion mass spectroscopy shows the presence of Mg near the top and bottom surfaces of the Cu (In,Ga) Se2 film. They hypothesize that the decrease in carrier concentration is due to compensation doping of the Cu-poor Cu (In,Ga) Se 2 by Mg. Optimizing sputtering conditions to reduce surface damage and Mg migration eliminates the interface states and restores the carrier concentration, resulting in device performance comparable to those with a ZnO window.
|Number of pages||6|
|Journal||Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures|
|Publication status||Published - 2009|
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Electrical and Electronic Engineering