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We experimentally demonstrate photoluminescence imaging using a silicon line-scanning camera. The narrow rectangular geometry of the sensor effectively lowers the image-blur, while keeping the sensitivity relatively high. Line scanning is demonstrated to provide sharp and high contrast images. To maintain fast measurement speeds, higher injections are used to compensate for the lower sensitivity of a line-scan measurement, where localized parts of the image are acquired sequentially. However, low-injection measurements remain possible at the expense of slower scan speeds if cooling is applied to the sensor. Using a detailed point-spread analysis and deconvolution, we quantify and correct for the remaining light spreading effects. Experimental results suggest an effective suppression of the cumulative nonlocal point spread commonly observed using area sensors, confirming silicon (Si) line sensors to be only susceptible to local point spreading effects.

In this work, crystallographic orientation of polycrystalline silicon films on glass formed by continuous wave diode laser crystallization was studied. Most of the grain boundaries were coincidence lattice Σ3 twin boundaries and other types of boundaries such as, Σ6, Σ9, and Σ21 were also frequently observed. The highest photoluminescence signal and mobility were observed for a grain with (100) orientation in the normal direction. X-ray diffraction results showed the highest occupancies between 41 and 70% along the (110) orientation. However, the highest occupancies changed to (100) orientation when a 100 nm thick SiOx capping layer was applied. Suns-Voc measurement and photoluminescence showed that higher solar cell performance is obtained from the cell crystallized with the capping layer, which is suspected from increased occupancies of (100) orientation.

When silicon solar cells are investigated by electro- or photoluminescence (PL) imaging using a silicon-based camera, photon scattering in the detector chip leads to a certain degree of blurring of the images, which can be removed by image deconvolution. The necessary point spread function (PSF) was originally measured directly by evaluating fine light spots, but this procedure needed the evaluation of several images. It was shown recently that evaluating an image with a sharp contrast edge in the middle may lead to a PSF spreading over longer distances by evaluating only one image. Here, we show that the previous backwards substitution method for obtaining this PSF does still lead to residual errors. An alternative method to derive the PSF from a measured contrast edge image is introduced here. It uses an iterative method, which leads to most precise results. In addition to the local deconvolution, nonlocal (homogeneous) light scattering is corrected. The correct reconstruction of the dark part of the image used for obtaining the PSF is a proof for the accuracy of this PSF.

Photoluminescence (PL) imaging over a large area (4.5×4.5 cm 2 ) is demonstrated on polycrystalline silicon thin films and solar cells on glass. PL imaging is a well-established technique for characterisation of silicon wafers and wafer-based solar cells, however its application to crystalline silicon thin films on glass was not possible due to low material quality and volume, and IR noise from the glass substrate. This paper reports methods to overcome these limitations, the design of a thin-film silicon PL imaging system, examples of PL images of silicon films at different processing stages and preliminary findings. It is demonstrated that the observed PL images qualitatively correlate with the silicon film crystal grain structure and quality.

The paper presents a review of major features of the crystalline silicon on glass (CSG) technology, its achievements, limitations and challenges, and latest developments. CSG cells are fabricated by solid-state crystallisation (SPC) of 1.5–3.5 µm thick precursor diodes prepared by PECVD or ebeam evaporation followed by thermal annealing, hydrogen passivation and metallisation. The highest efficiency of 10.4% was demonstrated on a PECVD minimodule on textured borosilicate glass. The best performing ebeam-evaporated cells on planar glass reached 8.6% efficiency. CSG cells were also produced on low-cost soda-lime glass with 8.1% and 7.1% efficiencies on PECVD and ebeam material respectively. The performance of SPC CSG cells is limited to below 11% because high defect density in SPC material limits V OC and 1.5–3.5 µm cell thickness limits J SC . A breakthrough came about when thicker poly-Si films with low defect density on glass were prepared by liquid-phase crystallisation (Amkreutz, 2011) leading to development of the next generation, liquid-phase crystallised silicon on glass (LPCSG) solar cells. The best performing LPCSG cells are made by line-focus laser crystallisation of 10 µm thick ebeam silicon films on dielectric layer coated borosilicate glass. High material quality is confirmed by low defect density observed in TEM images, high carrier mobilities, and minority carrier lifetime longer than 260 ns. An intermediate dielectric layer can be SiC x , SiO x , SiN x or their combination and its properties are crucial for cell fabrication and performance. Dopants are introduced into the LPCSG cell absorber either during film deposition or diffused from doped intermediate layer during crystallisation. Light-trapping texture is formed on the exposed silicon surface by wet etching. A cell emitter is created by diffusion from spin-on-dopant source. Cell metallisation is based on point contacts between Al and cell emitter and absorber accessed through vias etched through cell layers to different depths. LPCSG cells outperformed CSG cells, with record V OC of 585 mV and efficiency of 11.7%. Efficiencies above 13% are achievable by improving light-coupling and contacting.

Luminescence imaging is a widely used characterization technique for silicon photovoltaics. However, the tools used to acquire images typically utilize a silicon CCD array for detection, which is a poor absorber at silicon luminescence wavelengths. This leads to a smearing effect in the measured image which can be characterized by a point spread function (PSF). If the true PSF is known then the measured image can be restored through deconvolution. Several methods exist for determining a PSF for a particular imaging system and different extraction techniques can lead to variations in the PSF result, yet no studies have provided comprehensive analysis of PSF deconvolution accuracy when applied to luminescence imaging. In this work, several new techniques have been designed and investigated in order to test PSF deconvolution results, with a view to quantifying improvement or errors generated and potentially leading towards improved image restoration.

We have developed an all-laser processing technique by means of two industrially-relevant continuous-wave fiber lasers operating at 1070 nm. This approach is capable of both substrate heating with a large defocused beam and material processing with a second scanned beam, and is suitable for a variety of photovoltaic applications. We have demonstrated this technique for rapid crystallization of thin film (~10 μm) silicon on glass, which is a low cost alternative to wafer-based solar cells. We have also applied this technique to wafer silicon to control dopant diffusion at the surface region where the focused line beam rapidly melts the substrate that then regrows epitaxially. Finite element simulations have been used to model the melt depth as a function of preheat temperature and line beam power. This process is carried out in tens of seconds for an area approximately 10 cm 2 using only about 1 kW of total optical power and is readily scalable. In this paper, we will discuss our results with both c-Si wafers and thin-film silicon.

Enrichment of vitamin D2 in Agaricus bisporus white button mushroom (WBM) using continuous UV light needs a longer exposure time, which can lead to discoloration. Using a Xenon pulsed UV light source, the yield of vitamin D2 was evaluated in freshly harvested button mushrooms and mushroom slices after exposure to 2.5, 3, 6 and 9 pulses of UV light at an average dose of 1.150 J/cm2 energy per pulse. Increase in vitamin D2 content was proportionate to the number of pulses of UV light. There was no difference in the vitamin D2 content of mushrooms between 200 g and 500 g punnets for the corresponding number of pulses (737 ± 81, 847 ± 38, 1148 ± 182, 1611 ± 444% versus 747 ± 48, 911 ± 35, 1307 ± 109, 2028 ± 181% Daily Value/serving, respectively; P > 0.05). Mushrooms in the top layer showed significantly higher amounts of vitamin D2 content than those in the bottom layer of a 500 g punnet (657 ± 22, 796 ± 76, 1433 ± 138, 1878 ± 178% versus 129 ± 60, 237 ± 117, 403 ± 35, 830 ± 257% DV/serving, respectively; P

Luminescence imaging is currently being used to provide spatially resolved defect in high volume silicon solar cell production. One option to obtain the high throughput required for on the fly detection is the use a silicon line scan cameras. However, when using a silicon based camera, the spatial resolution is reduced as a result of the weakly absorbed light scattering within the camera's chip. This paper address this issue by applying deconvolution from a measured point spread function. This paper extends the methods for determining the point spread function of a silicon area camera to a line scan camera with charge transfer. The improvement in resolution is quantified in the Fourier domain and in spatial domain on an image of a multicrystalline silicon brick. It is found that light spreading beyond the active sensor area is significant in line scan sensors, but can be corrected for through normalization of the point spread function. The application of this method improves the raw data, allowing effecti...

Luminescence imaging of Silicon solar cells is typically performed with a silicon CCD, which is a poor absorber of silicon luminescence (900-1300 nm). This leads to a phenomenon referred to as photon smearing in the CCD, where a photon incident on one pixel may be absorbed in another. This makes the image blurry and quantitative analysis of this data inaccurate. Also resolution, contrast, and sharpness of the image are reduced at features such as grain boundaries, and sample edges. An already established method of recovering the original luminescence signal incident on the CCD is to deconvolve a Point Spread Function (PSF) with the resultant image. This paper focuses on a novel method for determining the PSF from a measurement of the Edge Spread Function, which greatly increases the Signal to Noise ratio over methods where the PSF is measured directly. The determined PSF and its application to luminescence images, is compared and contrasted with previously published PSF determination methods.

In this paper, the effect of phosphorus diffusion and hydrogen passivation on the material properties of laser crystallised silicon on glass is investigated. Photoluminescence imaging, as well as Hall effect and Suns-Voc techniques are applied for the characterisation of laser crystallized silicon thin-film material properties. Hall effect as well as Suns-Voc measurements supports the photoluminescence imaging results; phosphorus diffusion and hydrogen passivation of laser crystallized films improves the overall material quality. Hydrogen passivation is more effective at improving the electronic properties of the laser crystallized films than phosphorus diffusion. Hydrogen passivated samples improved the photoluminescence intensity even further by a factor of 3. In addition, a correlation between photoluminescence intensity and open-circuit voltage is demonstrated: samples with highest photoluminescence intensity (1678 counts/s), gave the highest voltage (530 mV). Hall effect measurement shows a significant improvement in the bulk material, with carrier mobility increasing from 208 cm2/Vs to 488 cm2/Vs.

Only recently, the quality of liquid phase crystallized silicon directly on glass substrates made a huge leap towards the quality of multi-crystalline wafers with open circuit voltages well above 600 mV. In this paper, we investigate the material quality in order to identify the factors limiting further performance improvements. We employ photoluminescence imaging on a state of the art test structure with lifetime calibration by transient photoluminescence. The resulting lifetime map is converted into an effective diffusion length map and the origin of regions with short lifetimes is investigated with electron backscattering and transmission electron microscopy. High local dislocation densities in areas with dissociated coincidence site lattice boundaries were found to be responsible for the localised quenching of the photoluminescence signal.