Experimental setup for camera-based measurements of electrically and optically stimulated luminescence of silicon solar cells and wafers

We report in detail on the luminescence imaging setup developed within the last years in our laboratory. In this setup, the luminescence emission of silicon solar cells or silicon wafers is analyzed quantitatively. Charge carriers are excited electrically (electroluminescence) using a power supply for carrier injection or optically (photoluminescence) using a laser as illumination source. The luminescence emission arising from the radiative recombination of the stimulated charge carriers is measured spatially resolved using a camera. We give details of the various components including cameras, optical filters for electro- and photo-luminescence, the semiconductor laser and the four-quadrant power supply. We compare a silicon charged-coupled device (CCD) camera with a back-illuminated silicon CCD camera comprising an electron multiplier gain and a complementary metal oxide semiconductor indium gallium arsenide camera. For the detection of the luminescence emission of silicon we analyze the dominant noise sources along with the signal-to-noise ratio of all three cameras at different operation conditions. © 2011 American Institute of Physics

Luminescence emission from forward- and reverse-biased multicrystalline silicon solar cells

We study the emission of light from industrial multicrystalline silicon solar cells under forward and reverse biases. Camera-based luminescence imaging techniques and dark lock-in thermography are used to gain information about the spatial distribution and the energy dissipation at pre-breakdown sites frequently found in multicrystalline silicon solar cells. The pre-breakdown occurs at specific sites and is associated with an increase in temperature and the emission of visible light under reverse bias. Moreover, additional light emission is found in some regions in the subband-gap range between 1400 and 1700 nm under forward bias. Investigations of multicrystalline silicon solar cells with different interstitial oxygen concentrations and with an electron microscopic analysis suggest that the local light emission in these areas is directly related to clusters of oxygen. © 2009 American Institute of Physics

Efficient Numerical Self-consistent Mean-field Approach for Fermionic Many-body Systems by Polynomial Expansion on Spectral Density

We propose an efficient numerical algorithm to solve Bogoliubov de Gennes equations self-consistently for inhomogeneous superconducting systems with a reformulated polynomial expansion scheme. This proposed method is applied to typical issues such as a vortex under randomly distributed impurities and a normal conducting junction sandwiched between superconductors. With various technical remarks, we show that its efficiency becomes remarkable in large-scale parallel performance.Comment: 16 pages, 5 figures (published version

Metabolic profiling shows pre-existing mitochondrial dysfunction contributes to muscle loss in a model of ICU acquired weakness

Background:Surgery can lead to significant muscle loss,which increasesrecovery time and associateswith increased mortality. Muscle lossis not uniform,with some patients losing significant muscle mass and others losing relatively little, andis likely to be accompanied by marked changes in circulating metabolitesand proteins. Determining these changes may help understand the variability and identify novel therapeutic approachesor markers of muscle wasting.Methods:To determine the association between muscle loss and circulating metabolites we studied 20 male patients (median age,70.5, inter-quartile range,62.5-75)undergoing aortic surgery. Muscle mass was determined before and 7 days after surgery and blood samples were taken before surgery, and 1, 3 and 7 days after surgery. The circulating metabolome and proteome were determined using commercial services (Metabolon and SOMAlogic). Results:Ten patients lost more than 10% of the cross-sectional area of the rectus femoris (RFCSA) and were defined as wasting. Metabolomic analysisshowed 557 circulatingmetabolites were altered following surgery (q<0.05) in the whole cohort and 104 differed between wasting and non-wasting patients (q<0.05).Weighted genome co-expression network analysis,identified clusters of metabolites, both before and after surgery, that associated with muscle mass and function(r=-0.72, p=6x10-4with RFCSAon day 0, p=3x10-4with RFCSAon day 7 and r=-0.73, p=5x10-4with hand-grip strength on day 7). These clusters were mainly composed of acyl carnitines and dicarboxylates indicating that pre-existing mitochondrial dysfunction contributes to muscle loss following surgery. Surgery elevated cortisolto the same extent in wasting and non-wasting patients but the cortisol:cortisone ratio was higher in the wasting patients (day 3 p=0.043 and day 7 p=0.016).Wasting patients also showed a greater increase in circulating nucleotides3 days after surgery. Comparison of the metabolome with inflammatory markers identified by SOMAscanÒshowed that pre-surgicalmitochondrial dysfunction was associated with GDF-15 (r=0.79, p=2 x 10-4)and thatGDF-15, IL-8, CCL-23 and IL-15RA contributed to metabolic changes in response to surgery. Conclusions:Weshow that pre-existing mitochondrial dysfunction andreduced cortisol inactivationcontribute to muscle loss following surgery.The data also implicate GDF-15 and IL-15RA in mitochondrial dysfunction

Luminescence imaging for quantitative solar cell material and process characterization

Electro (EL) and photoluminescence (PL) imaging are rather new methods for fast spatially resolved characterization of the electrical properties of crystalline silicon solar cells. EL imaging is experimentally quite simple. Unfortunately in general a quantitative evaluation of the diode quality is not possible, but is limited to very low quality devices. Conversely, PL imaging is experimentally more challenging but allows also a quantitative evaluation of the diode quality for state-of-the-art devices. Experimentally the two techniques are compared analyzing two differently processed solar cells made of multi crystalline sister wavers

Interlaboratory comparison of short-circuit current versus irradiance linearity measurements of photovoltaic devices

This work presents the results of the first interlaboratory comparison of linearity measurements of short-circuit current versus irradiance that includes a wide variety of photovoltaic (PV) device types, from reference cells to full-size modules. The aim of this inter-comparison was to compare the methods employed and to collect new inputs useful for the revision of the standard IEC 60904-10, which deals with linearity measurements for PV devices. The procedures and facilities employed by the partners include the differential spectral responsivity, the white light response, the solar simulator method and the two-lamp method. The facilities are generically described and compared and their main sources of uncertainty are discussed. Comparison results show good agreement within declared uncertainties between all partners. A few minor exceptions under low-light conditions raise questions of possible uncertainty underestimation for these specific conditions. The overall outcome of the comparison also highlights the importance of considering correlations in the uncertainty budget, which can potentially improve the overall stated uncertainty. A critical review is made of the data analysis adopted in the standard IEC 60904-10 to calculate the linearity degree of the short-circuit current towards irradiance. The analysis review suggests a way to make results based on different methods more comparable and less prone to erroneous linearity assessment