The ability to probe morphology and phase distribution in complex systems at multiple length scales unravels the interplay of nano- and micrometer-scale factors at the origin of macroscopic behavior. While different electron- and X-ray-based imaging techniques can be combined with spectroscopy at high resolutions, owing to experimental time limitations the resulting fields of view are too small to be representative of a composite sample. Here a new X-ray imaging set-up is proposed, combining full-field transmission X-ray microscopy (TXM) with X-ray absorption near-edge structure (XANES) spectroscopy to follow two-dimensional and three-dimensional morphological and chemical changes in large volumes at high resolution (tens of nanometers). TXM XANES imaging offers chemical speciation at the nanoscale in thick samples (>20 µm) with minimal preparation requirements. Further, its high throughput allows the analysis of large areas (up to millimeters) in minutes to a few hours. Proof of concept is provided using battery electrodes, although its versatility will lead to impact in a number of diverse research fields.

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Three-dimensional imaging of chemical phase transformations at the nanoscale with full-field transmission X-ray microscopy

Silicon wafer solar cells continue to be the leading photovoltaic technology, and in many places are now providing a substantial portion of electricity generation. Further adoption of this technology will require processing that minimises losses in device performance. A fundamental mechanism for efficiency loss is the recombination of photo-generated charge carriers at the unavoidable cell surfaces. Dielectric coatings have been shown to largely prevent these losses through a combination of different passivation mechanisms. This review aims to provide an overview of the dielectric passivation coatings developed in the past two decades using a standardised methodology to characterise the metrics of surface recombination across all techniques and materials. The efficacy of a large set of materials and methods has been evaluated using such metrics and a discussion on the current state and prospects for further surface passivation improvements is provided.

/pdf/dielectric-surface-passivation-for-silicon-solar-cells-a-zv6y6fla1t.pdf

Dielectric surface passivation for silicon solar cells: A review

D.M. is supported by an Australian Research Council
QEII Fellowship. The Centre of Excellence for Advanced
Silicon Photovoltaics and Photonics at UNSW is funded by
the Australian Research Council.

https://openresearch-repository.anu.edu.au/bitstream/1885/95091/1/01_Macdonald_Imaging_interstitial_iron_2008.pdf

Imaging interstitial iron concentrations in boron-doped crystalline silicon using photoluminescence

Motivated by the challenge of capturing complex hierarchical chemical detail in natural material from a wide range of applications, the Maia detector array and integrated realtime processor have been developed to acquire X-ray fluorescence images using X-ray Fluorescence Microscopy (XFM). Maia has been deployed initially at the XFM beamline at the Australian Synchrotron and more recently, demonstrating improvements in energy resolution, at the P06 beamline at Petra III in Germany. Maia captures fine detail in element images beyond 100 M pixels. It combines a large solid-angle annular energy-dispersive 384 detector array, stage encoder and flux counter inputs and dedicated FPGA-based real-time event processor with embedded spectral deconvolution. This enables high definition imaging and enhanced trace element sensitivity to capture complex trace element textures and place them in a detailed spatial context. Maia hardware and software methods provide per pixel correction for dwell, beam flux variation, dead-time and pileup, as well as off-line parallel processing for enhanced throughput. Methods have been developed for real-time display of deconvoluted SXRF element images, depth mapping of rare particles and the acquisition of 3D datasets for fluorescence tomography and XANES imaging using a spectral deconvolution method that tracks beam energy variation.

https://iopscience.iop.org/article/10.1088/1742-6596/499/1/012002/pdf

Maia X-ray fluorescence imaging: Capturing detail in complex natural samples

The absorption factor of crystalline silicon PV cells: A numerical and experimental study

Electroluminescence (EL) and photoluminescence (PL) imaging have recently been demonstrated to be fast experimental techniques that allow measurement of the spatial distribution of the diffusion length in silicon solar cells and of the minority carrier lifetime in large area silicon wafers (1, 2). A practical advantage of these techniques is that data acquisition times for high resolution luminescence images are typically on the order of only one second. This paper reviews previous work related to process monitoring by luminescence imaging techniques and discusses some recent progress in the areas of several experimental and theoretical aspects of luminescence imaging. It is shown that luminescence imaging is an exceptionally versatile tool that provides spatially resolved information about a variety of material and solar cell parameters with data acquisition times that are compatible with in-line process monitoring.

Progress with luminescence imaging for the characterisation of Silicon wafers and solar cells

The electronic properties of multi-crystalline silicon must be improved during solar cell fabrication if highly efficient devices are to be made. This work shows how gettering and silicon nitride induced hydrogenation improve three properties: carrier lifetime, interstitial iron concentration, and trap density. Area averaged effective carrier lifetimes less than 10 µs were improved to greater than 60 µs. A tenfold reduction in trap densities was achieved. Photoluminescence images showing the influence processing techniques have on the electronic properties of the silicon are presented. Copyright © 2007 John Wiley & Sons, Ltd.

/pdf/on-the-electronic-improvement-of-multi-crystalline-silicon-b2ps68pl14.pdf

On the electronic improvement of multi‐crystalline silicon via gettering and hydrogenation

Evaluation of the Bulk Lifetime of Silicon Wafers by Immersion in Hydrofluoric Acid and Illumination

This paper presents new data regarding the formation rate of iron–boron (Fei–B) pairs in p-type crystalline silicon. Improvements in the temperature control of the sample, a reduction in measurement error of the effective lifetime of the sample after all Fei–B pairs have reformed, and improved statistical analysis have led to a revision of the value of the pre-factor in the equation relating the association time constant of iron–acceptor pairs to the acceptor concentration. The new equation predicts a 14% slower repairing time than a previous commonly used equation, and reduces the uncertainty in determining the acceptor concentration from the repairing time from ±24% to ±7%.

/pdf/accurate-measurement-of-the-formation-rate-of-iron-boron-2x6l42f9nh.pdf

Jason Tan

Papers

Imaging interstitial iron concentrations in boron-doped crystalline silicon using photoluminescence

Progress with luminescence imaging for the characterisation of Silicon wafers and solar cells

On the electronic improvement of multi‐crystalline silicon via gettering and hydrogenation

Evaluation of the Bulk Lifetime of Silicon Wafers by Immersion in Hydrofluoric Acid and Illumination

Accurate measurement of the formation rate of iron–boron pairs in silicon