| 1. |
- Bertoni, M. I., 1967-, et al.
(författare)
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Nanoprobe X-ray fluorescence characterization of defects in large-area solar cells
- 2011
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Ingår i: Energy & Environmental Science. - : Royal Society of Chemistry (RSC). - 1754-5692 .- 1754-5706. ; 4, s. 4252-4257
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Tidskriftsartikel (refereegranskat)abstract
- The performance of centimeter-sized energy devices is regulated by inhomogeneously distributednanoscale defects. To improve device efficiency and reduce cost, accurate characterization of thesenanoscale defects is necessary. However, the multiscale nature of this problem presentsa characterization challenge, as non-destructive techniques often specialize in a single decade of lengthscales, and have difficulty probing non-destructively beneath the surface of materials with sub-micronspatial resolution. Herein, we push the resolution limits of synchrotron-based nanoprobe X-rayfluorescence mapping to 80 nm, to investigate a recombination-active intragranular defect in industrialsolar cells. Our nano-XRF measurements distinguish fundamental differences between benign anddeleterious dislocations in solar cell devices: we observe recombination-active dislocations to containa high degree of nanoscale iron and copper decoration, while recombination-inactive dislocationsappear clean. Statistically meaningful high-resolution measurements establish a connection betweencommercially relevant materials and previous fundamental studies on intentionally contaminatedmodel defect structures, pointing the way towards optimization of the industrial solar cell process.Moreover, this study presents a hierarchical characterization approach that can be broadly extended toother nanodefect-limited energy systems with the advent of high-resolution X-ray imaging beamlines
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| 2. |
- Castellanos, Sergio, et al.
(författare)
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Inferring Dislocation Recombination Strength in Multicrystalline Silicon via Etch Pit Geometry Analysis
- 2014
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Ingår i: 2014 IEEE 40TH Photovoltaic Specialists Conference (PVSC). - : IEEE. - 9781479943982 ; , s. 2957-2959
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Konferensbidrag (refereegranskat)abstract
- Dislocations limit solar cell performance by decreasing minority carrier diffusion length, leading to inefficient charge collection at the device contacts [1]. However, studies have shown that the recombination strength of dislocation clusters within millimeters away from each other can vary by orders of magnitude [2]. In this contribution, we present correlations between dislocation microstructure and recombination activity levels which span close to two orders of magnitude. We discuss a general trend observed: higher dislocation recombination activity appears to be correlated with a higher degree of impurity decoration, and a higher degree of disorder in the spatial distribution of etch pits. We present an approach to quantify the degree of disorder of dislocation clusters. Based on our observations, we hypothesize that the recombination activity of different dislocation clusters can be predicted by visual inspection of the etch pit distribution and geometry.
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| 3. |
- Castellanos, Sergio, et al.
(författare)
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Variation of dislocation etch-pit geometry : An indicator of bulk microstructure and recombination activity in multicrystalline silicon
- 2014
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 115:18, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- Dislocation clusters in multicrystalline silicon limit solar cell performance by decreasing minoritycarrier diffusion length. Studies have shown that the recombination strength of dislocation clusterscan vary by up to two orders of magnitude, even within the same wafer. In this contribution, wecombine a surface-analysis approach with bulk characterization techniques to explore theunderlying root cause of variations in recombination strength among different clusters. We observethat dislocation clusters with higher recombination strength consist of dislocations with a largervariation of line vector, correlated with a higher degree of variation in dislocation etch-pit shapes(ellipticities). Conversely, dislocation clusters exhibiting the lowest recombination strength containmostly dislocations with identical line vectors, resulting in very similar etch-pit shapes. Thedisorder of dislocation line vector in high-recombination clusters appears to be correlated withimpurity decoration, possibly the cause of the enhanced recombination activity. Based on ourobservations, we conclude that the relative recombination activity of different dislocation clustersin the device may be predicted via an optical inspection of the distribution and shape variation ofdislocation etch pits in the as-grown wafer.
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| 4. |
- Fenning, D. P., et al.
(författare)
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Iron distribution in silicon after solar cell processing: Synchrotron analysis and predictive modelling
- 2011
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 98, s. 162103-
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Tidskriftsartikel (refereegranskat)abstract
- The evolution during silicon solar cell processing of performance-limiting iron impurities isinvestigated with synchrotron-based x-ray fluorescence microscopy. We find that during industrialphosphorus diffusion, bulk precipitate dissolution is incomplete in wafers with high metal content,specifically ingot border material. Postdiffusion low-temperature annealing is not found to alterappreciably the size or spatial distribution of FeSi2precipitates, although cell efficiency improvesdue to a decrease in iron interstitial concentration. Gettering simulations successfully modelexperiment results and suggest the efficacy of high- and low-temperature processing to reduce bothprecipitated and interstitial iron concentrations, respectively.
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| 5. |
- Lazić, Predrag, 1975-, et al.
(författare)
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Low intensity conduction states in FeS2 : implications for absorption, open-circuit voltage and surface recombination
- 2013
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Ingår i: Journal of Physics. - : Institute of Physics (IOP). - 0953-8984 .- 1361-648X. ; 25:46, s. 465801-
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Tidskriftsartikel (refereegranskat)abstract
- Pyrite (FeS2), being a promising material for future solar technologies, has so far exhibited in experiments an open-circuit voltage (OCV) of around 0.2 V, which is much lower than the frequently quoted 'accepted' value for the fundamental bandgap of similar to 0.95 eV. Absorption experiments show large subgap absorption, commonly attributed to defects or structural disorder. However, computations using density functional theory with a semi-local functional predict that the bottom of the conduction band consists of a very low intensity sulfur p-band that may be easily overlooked in experiments because of the high intensity onset that appears 0.5 eV higher in energy. The intensity of absorption into the sulfur p-band is found to be of the same magnitude as contributions from defects and disorder. Our findings suggest the need to re-examine the value of the fundamental bandgap of pyrite presently in use in the literature. If the contribution from the p-band has so far been overlooked, the substantially lowered bandgap would partly explain the discrepancy with the OCV. Furthermore, we show that more states appear on the surface within the low energy sulfur p-band, which suggests a mechanism of thermalization into those states that would further prevent extracting electrons at higher energy levels through the surface. Finally, we speculate on whether misidentified states at the conduction band onset may be present in other materials.
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| 6. |
- Lindroos, Jeanette, 1983-, et al.
(författare)
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Nickel : A very fast diffuser in silicon
- 2013
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 113:20
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Tidskriftsartikel (refereegranskat)
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| 7. |
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| 8. |
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