Entwicklung von amorphen Silizium-Germanium-Legierungen für den Einsatz in Stapelsolarzellen

To obtain high efficiency silicon based thin film solar cells, the conceptof stacked solar cells is routinely used. The use of component cells with different opticalbandgaps provides a better utilization of the solar spectrum. In a stacked cell structure,a high quality narrow bandgap material is needed for the active layer of the bottom cell.Amorphous silicon-germanium-alloys (a-SiGe:H) have been successfully employed becauseof their tunable optical bandgap E$_{G}$ between 1.8 eV (a-Si:H) and 1.1 eV (a-Ge:H).Considerable effort has been put into the development of a-SiGe:H. Still, with increasingG$_{e}$ content, the material shows a characteristic deterioration of its electronic properties,like an exponential increase of the defect density, thus counteracting the gain in absorptionobtained for higher G$_{e}$ contents. It is the defect density which has the dominant influenceon carrier transport and cell efficiency by affecting the mobility lifetime product and theelectric field in the devices.The performance of a-SiGe:H pin solar cells with a wide range of Ge contents i.e. awide range of optical band gaps (E$_{G}$ = 1.3 to 1.6 eV) are compared. It is demonstratedhow the deterioration of the material properties can be overcome by careful adjustment ofthe device design and the use of highly reflective ZnO/Ag back contacts

A-Si:H buffer in a-SiGe:H solar cells

Profiled a-SiGe:H-buffer layers between the doped and the absorption layers of amorphous silicon germanium (a-SiGe:H) solar cells are routinely used to avoid bandgap discontinuities and high-defect densities at the p/i- and i/n interface. Here, we present a much simpler approach replacing the profiled a-SiGe:H-buffer layers at both interfaces by a-Si:H-buffer layers. It is demonstrated that for a-SiGe:H solar cells (thickness of the E-G=1.5 eV part is 54 nm) these structures yield similar open circuit voltage V-OC and fill factor (FF) compared to the bandgap profiled layer at the same short circuit current density j(SC). The influence of thickness, optical bandgap and position of the buffer layers on the solar cell performance is investigated. (C) 2002 Elsevier Science B.V. All rights reserved

St. John's Daily Star, 1919-07-30

The St. John's Daily Star was published daily except Sunday between 17 April 1915 - 23 July 1921