Multi-trench-based technique to improve amorphous SiGe thin-film solar cell performance
In order to improve the electrical performance of the conventional amorphous SiGe thin-film solar cells, a new multi-trench technique has been proposed. In this method, the multi-trench is created in the intrinsic SiGe layer and filled with p-type doped Si. The p-type trenches in the intrinsic SiGe layer improve the electrical performance of the proposed design. Electrical characteristics of the proposed structure are analyzed and optimized by 2-D numerical modeling and compared with conventional amorphous SiGe thin-film solar cell characteristics. The extracted results show that the multi-trench-based technique has excellent effect on the fill factor and efficiency of the device.
Electrical defect study in thin-film SiGe/Si solar cells
Abstract We have investigated the presence of defects and their role on the efficiency of thin-film SiGe/Si solar cells. Temperature-dependent I–V, and DLTS measurements revealed the presence of a main defect that introduces a deep acceptor level (0/-) near the mid-gap of SiGe, at E v +0.45 eV . We show that this level is responsible for the generation–recombination current observed in our solar cells. We demonstrate that this defect is sensitive to passivation and that its concentration reduces with hydrogenation. Finally, we show that this level plays an important role in the determination of the minority carrier lifetime in our devices.
Imaging the Internal Structure of an Alpine Glacier via L-Band Airborne SAR Tomography
In this paper, we report results from the analysis of 3-D L-band airborne synthetic aperture radar (SAR) acquisitions acquired in March 2014 over the Mittelbergferner glacier, Austrian Alps, during the European Space Agency (ESA) campaign AlpTomoSAR. The campaign included coincident in situ measurements of snow and ice properties and ground-penetrating radar (GPR) data acquired at 600 and 200 MHz over a total length of 18 km. Radar data were acquired by repeatedly flying an L-band SAR along an oval racetrack at an altitude of about 1300 m over the glacier, such that two data stacks from opposite views are obtained. Data from all passes were coherently combined to achieve 3-D resolution capabilities, resulting in the generation of 3-D tomographic SAR (TomoSAR) cubes, where each voxel represents L-band radar reflectivity from a particular location in the 3-D space at a spatial resolution on the order of meters. TomoSAR cubes were finally corrected to account for wave propagation velocity into the ice, which was a necessary step to associate the observed features with their geometrical location, hence enabling a direct comparison to GPR data. The TomoSAR cubes show the complexity of the glacier subsurface scattering. Most areas are characterized by surface scattering in proximity of the ice surface, plus a complex pattern of in-depth volumetric scattering beneath and scattering at the ice/bedrock interface. Various subsurface features observed in GPR transects at 200 MHz clearly showed up in TomoSAR sections as well, particularly firn bodies, crevasses, layer transitions, and bedrock reflection down to 50 m below the ice surface.