RESUMEN
Enhancing the probing depth of photoemission studies by using hard X-rays allows the investigation of buried interfaces of real-world device structures. However, it also requires the consideration of photoelectron-signal attenuation when evaluating surface effects. Here, we employ a computational model incorporating surface band bending and exponential photoelectron-signal attenuation to model depth-dependent spectral changes of Si 1s and Si 2s core level lines. The data were acquired from hydrogenated boron-doped microcrystalline thin-film silicon, which is applied in silicon-based solar cells. The core level spectra, measured by hard X-ray photoelectron spectroscopy using different excitation energies, reveal the presence of a 0.29 nm thick surface oxide layer. In the silicon film a downward surface band bending of eVbb = -0.65 eV over â¼6 nm obtained via inverse modeling explains the observed core level shifts and line broadening. Moreover, the computational model allows the extraction of the "real" Si 1s and Si 2s bulk core level binding energies as 1839.13 and 150.39 eV, and their natural Lorentzian line widths as 496 and 859 meV, respectively. These values significantly differ from those directly extracted from the measured spectra. Because band bending usually occurs at material surfaces we highly recommend the detailed consideration of signal integration over depth for quantitative statements from depth-dependent measurements.
RESUMEN
The influence of realistic interface morphologies on light trapping in amorphous silicon thin-film solar cells with periodic surface textures is studied. Realistic interface morphologies are obtained by a 3D surface coverage algorithm using the substrate morphology and layer thicknesses as input parameters. Finite difference time domain optical simulations are used to determine the absorption in the individual layers of the thin-film solar cell. The influence of realistic interface morphologies on light trapping is determined by using solar cells structures with the same front and back contact morphologies as a reference. Finally the optimal surface textures are derived.
RESUMEN
A three-dimensional model that predicts the interface morphologies of silicon thin-film solar cells prepared on randomly textured substrates was developed and compared to experimental data. The surface morphologies of silicon solar cells were calculated by using atomic force microscope scans of the textured substrates and the film thickness as input data. Calculated surface morphologies of silicon solar cells are in good agreement with experimentally measured morphologies. A detailed description of the solar cell interface morphologies is necessary to understand light-trapping in silicon single junction and micromorph tandem thin-film solar cells and derive optimal light-trapping structures.
RESUMEN
We present an algorithm for generating a surface approximation of microcrystalline silicon (µc-Si) layers after plasma enhanced chemical vapor deposition (PECVD) onto surface textured substrates, where data of the textured substrate surface are available as input. We utilize mathematical image processing tools and combine them with an ellipsoid generator approach. The presented algorithm has been tuned for use in thin-film silicon solar cell applications, where textured surfaces are used to improve light trapping. We demonstrate the feasibility of this method by means of optical simulations of generated surface textures, comparing them to simulations of measured atomic force microscopy (AFM) scan data of both Aluminum-doped zinc oxide (AZO, a transparent and conductive material) and µc-Si layers.
RESUMEN
Chemical etching is widely applied to texture the surface of sputter-deposited zinc oxide for light scattering in thin-film silicon solar cells. Based on experimental findings from the literature and our own results we propose a model that explains the etching behavior of ZnO depending on the structural material properties and etching agent. All grain boundaries are prone to be etched to a certain threshold, that is defined by the deposition conditions and etching solution. Additionally, several approaches to modify the etching behavior through special preparation and etching steps are provided.