Material-induced shunts in multicrystalline silicon solar cells

By applying lock-in thermography imaging, light-beam-induced current imaging, electron-beam-induced current imaging at different stages of sample preparation, and infrared light microscopy in transmission mode, the physical nature of the dominant material-induced shunts in multicrystalline solar cells made from p-type silicon material has been investigated. It turns out that these shunts are due to silicon carbide (SiC) filaments, which grow preferentially in grain boundaries and cross the whole cell. These filaments are highly n-type doped, like the emitter layer on the surface of the cells. They are electrically connected both with the emitter and with the back contact, thereby producing internal shunts in the solar cell. The text was submitted by the authors in English.     

Series resistance imaging in solar cells by lock‐in thermography

Two operation modes of lock‐in thermography are introduced to detect regions of high series resistance in solar cells. These are differential techniques, working in the dark and under illumination, where images taken under two different conditions are used to calculate an image, which is especially sensitive to series resistance variations. Though the series resistance cannot be measured quantitatively by these techniques, regions of increased emitter contact resistance can be reliably detected. A realistic electrothermal modelling of a series resistance defect in a solar cell with and without illumination is presented. The new thermographic techniques are compared with established techniques for series resistance imaging. Especially the technique working under illumination gives results that agree very well with those of other methods. Copyright © 2005 John Wiley & Sons, Ltd.     

Improvement of signal-to-noise and contrast-to-noise ratios in dual-screen computed radiography

A dual-screen computed radiography (CR) technique has been developed to improve and optimize the overall image signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). With this technique, two CR screens are exposed together and separately scanned to form a front and a back image. These two images are then superimposed to form an image of improved SNR and CNR. A mathematical model has been derived to describe the improvement and optimization of the SNR and CNR. Based on this model, the front and back images should be weighted in proportion to their SNR squared to optimize the SNR of the composite image. Imaging experiments have been conducted to verify the theoretical model under mammographic and chest imaging conditions. The results largely agree with the theoretical predictions. It has also been found that optimization of the SNR results in nearly optimal CNR and vice versa. For mammographic imaging, a 14%-22% improvement in the SNR and a 13%-19% improvement in the CNR have been demonstrated. For chest imaging, a 31%-36% improvement in the SNR and a 28%-30% improvement in the CNR has been demonstrated.     

Impact of localized regions with very high series resistances on cell performance

The J–V curves recorded under illumination for solar cells having a high series resistance can appear shunted when a fraction of the cell area is affected by very high series resistance values. This “apparent shunting” behaviour was observed in n‐type rear‐junction, laser‐doped cells with light‐induced plated front contacts. Localized series resistance measurements of the affected cells by photoluminescence imaging revealed that over 20% of the cell area had a series resistance above 10 Ω cm² and extending up to a maximum value of 168 Ω cm². It was found that cells with localized series resistances have a detrimental impact on the FF and J_sc of the device. Furthermore, an unusual FF recovery was also observed with decreasing level of illumination. A solar cell model with localized high series resistances was developed to further study this “apparent shunting” behaviour with respect to its impact on cell performance. Copyright © 2011 John Wiley & Sons, Ltd.     

Fast and automatic object pose estimation for range images on the GPU

We present a pose estimation method for rigid objects from single range images. Using 3D models of the objects, many pose hypotheses are compared in a data-parallel version of the downhill simplex algorithm with an image-based error function. The pose hypothesis with the lowest error value yields the pose estimation (location and orientation), which is refined using ICP. The algorithm is designed especially for implementation on the GPU. It is completely automatic, fast, robust to occlusion and cluttered scenes, and scales with the number of different object types. We apply the system to bin picking, and evaluate it on cluttered scenes. Comprehensive experiments on challenging synthetic and real-world data demonstrate the effectiveness of our method.     

Scanning deep level transient spectroscopy (SDLTS)

Scanning Deep Level Transient Spectroscopy (SDLTS) is a current SEM technique for the detection of the local distribution of deep level centres in semiconductors. It is based on the application of the widely used Deep Level Transient Spectroscopy (DLTS), which enables capacitance changes (or current changes) to be measured in a space charge structure after an excitation pulse as a function of the temperature. This makes it possible to detect the energy levels and the concentration of electronic states in the band gap. By means of scanning DLTS–i.e. the excitation of the levels by an electron probe–deep level states can be investigated with a spatial resolution of a few microns. Scanning the pulsed electron beam (at a temperature selected according to an interesting energy level) yields an SDLTS image. Based on the general principle of the measurement and on the necessary instrumentation the practice of the SDLTS signal generation analysis is presented and experimental examples are discussed.     

Direct sputum analysis of Pseudomonas aeruginosa macrorestriction fragment genotypes in patients with cystic fibrosis

The distribution of bacterial populations in the airways of 13 patients with cystic fibrosis who were colonized for 6-23 years with Pseudomonas aeruginosa was investigated by genotyping of bacterial chromosomes directly isolated from 21 sputa. After removal of host material from sputum by hypotonic cell lysis and repetitive washing and centrifugation steps, agarose-embedded bacterial cells were lysed, residual eukaryotic DNA separated by field inversion gel electrophoresis, and the purified bacterial chromosomes subjected to macrorestriction fragment pattern and Southern analyses. Bacterial populations consisted of a single P. aeruginosa clone in 17 sputa, of which more than one clonal variant was apparent in two SpeI fragment fingerprints. Two clones of P. aeruginosa and another species co-existed in four samples. Genomically homogeneous populations of P. aeruginosa are characteristic for chronically colonized lungs in most cases of cystic fibrosis.     

Infrared lock-in thermography through glass substrates

Infrared lock-in thermography of an active layer through a glass substrates is demonstrated and explained theoretically. A transition between signal generation close to the active layer and close to the back surface of the substrate is found for glass at 0.5 Hz. For higher frequencies, the signal resolution is given by the thermal diffusion length in glass, very similar to direct observation of the active layer. An experimental difficulty is that the signal is strongly influenced by a slow but strong temperature transient in the beginning of the measurement. It is shown how to correct for this effect efficiently.