Optical mapping of large area thin film solar cells

Huang, Zhi-Quan; Chen, Jie; Sestak, Michelle N.; Attygalle, Dinesh; Dahal, Lila R.; Mapes, Meghan R.; Strickler, D.; Kormanyos, Kenneth R.; Salupo, Carl; Collins, R. W.

doi:10.1109/pvsc.2010.5616069

Cited by 9 publications

(6 citation statements)

References 8 publications

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“…The SnO 2 :F thickness was nearly the same for the two positions, within the range of 2694 ± 9 Å. Confidence limits and mean square errors (MSEs) for the two best fits are also given [23].…”

Section: To Pv Gigawattsmentioning

confidence: 94%

“…Off-line SE data have been collected from the film side over an ~ 40 x 80 cm 2 area of a Pilkington TEC-15 glass panel coated with CdS. These data have been analyzed using a five layer model with free parameters that include the bulk and surface roughness layer thicknesses of the CdS and the three layer thicknesses of the TEC-15 glass substrate, including the SnO 2 , SiO 2 , and SnO 2 :F [23]. The optical property parameters also incorporated in the modeling include the set of CdS CP broadening values which are linked to a single mean free path λ, and the Drude amplitude A D and width Γ D for the SnO 2 :F layer that enables determination of the scattering time, resistivity, and sheet resistance of the layer, the latter requiring measurement of the thickness as well.…”

Section: To Pv Gigawattsmentioning

confidence: 99%

“…The two plots (top and right) in both parts show parameter variations along the X and Y axes. The experimental spectra and best fit results for the two indicated points in (a) are shown inFigure 9[23].…”

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confidence: 99%

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Spectroscopic ellipsometry: metrology for photovoltaics from the nanoscale to gigawatts

Marsillac

Collins

2012

SPIE Proceedings

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Non-destructive, non-invasive measurement and monitoring tools, such as spectroscopic ellipsometry (SE), are needed at all scales of thin film photovoltaic (PV) technology development -from the nanometer scale that describes the electronic and physical structure of materials fabricated in research laboratories to the gigawatt scale that requires the large-area uniformity of materials made in mass production. In the research laboratory, real time SE during materials fabrication has provided insights into the structural and electronic property evolution, and dielectric functions of the thin films. Here we will present such results for the growth of thin film PV materials of various compositions and properties, including those used in the demanding I-III-VI 2 solar cell technology. In the PV manufacturing plant, mapping SE can be used to evaluate the uniformity of thickness and properties of the layers in full scale PV panels and even in completed modules. Here we will present representative results for the uniformity of CdS, the window layer in CdTe PV technology, which reached 1.4 GW annual production in 2010.

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Section: To Pv Gigawattsmentioning

confidence: 94%

Section: To Pv Gigawattsmentioning

confidence: 99%

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Spectroscopic ellipsometry: metrology for photovoltaics from the nanoscale to gigawatts

Marsillac

Collins

2012

SPIE Proceedings

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“…The plate was coated with a relatively thick layer of CdS, designed for the purposes of this demonstration. In order to assess the validity of the thickness variations as deduced by throughthe-glass SE, a comparison has been made with the corresponding map obtained by a film side measurement [11]. Film side data were translated in position so as to generate the correlation shown in Fig.…”

Section: Large Area Through-the-glass Measurementmentioning

confidence: 99%

Through-the-glass spectroscopic ellipsometry of superstrate solar cells and large area panels

Chen

Aryal

et al. 2011

2011 37th IEEE Photovoltaic Specialists Conference

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We have advanced the technique of through-the-glass spectroscopic ellipsometry (SE) toward the nondestructive, non-invasive analysis of large area coated glass plates and completed solar modules in the superstrate configuration. The focus of this work involves reducing the effects of artifacts due to changes in the polarization state of light as it traverses the glass to the film side. By including the effects of (i) strain in the glass, (ii) differences in soda lime glass optical properties at the tin side versus the film side, and (iii) possible collection of both tin side and film side reflections, the accuracy in the determination of film properties in through-the-glass measurements can be improved.For example, measurements of the index of refraction spectra of the uncoated film side glass using a through-the-glass method agree with direct measurements from the uncoated film side to within r0.004 over the full spectral range of through-the-glass measurements (~300 to 1600 nm).

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“…These effects are observable to the very small grain size, potentially high stress, and roughness of sputtered CdTe films. Now, work by the Toledo group is being done to measure full devices through the glass, and to measure large areas quickly [28,29]. This promises to offer realtime structural characterization of production scale modules in the manufacturing line.…”

Section: Background and Introductionmentioning

confidence: 99%

Optical measurement techniques for in-line process control in CdS/CdTe solar cell manufacturing

Kephart

Sampath

2011

2011 37th IEEE Photovoltaic Specialists Conference

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OPTICAL MEASUREMENT TECHNIQUES FOR IN-LINE PROCESS CONTROLIN CdS/CdTe SOLAR CELL MANUFACTURING CdS/CdTe solar cells have achieved gigawatt-scale commercial production at a lower cost than traditional crystalline silicon photovoltaics. With large-scale production of semiconductor devices, process control is critical to ensuring consistent quality. While there are many classes of materials characterization techniques including scanning probe, x-ray, electronic techniques, optical techniques are particularly promising for in-line structural characterization and process control. They are fast, non-contact, occupationally safe, precise, and can be performed immediately after film deposition to detect problems early in the manufacturing process.Two such optical techniques are examined here: spectroscopic ellipsometry and scanning white light interferometry. Spectroscopic ellipsometry consists of measuring the change in polarization of light reflected from a thin film structure. Fitting a model to the data provides structural information such as layer thickness and optical properties.Visually rough films can be a major obstacle to the use of ellipsometry, and processing options are explored to reduce roughness to acceptable levels. Ellipsometry has been shown to be accurate within 4% of thickness for the CdTe absorber layer and the CdS iii window layer can be measured accurately under the CdTe absorber for layers thicker than about 100 nm.Scanning white light interferometry (SWLI) uses the interference of reflected light from a surface to construct an extremely precise depth profile. This technique was examined for measurement of surface morphology and roughness as well as the measurement of film step heights, which could indicate whether or not the technique can be used for scribe metrology. Though the lateral resolution is limited by the use of optical microscopy, it has been shown that surface features can be resolved.Step height measurements match stylus profilometry very closely over a wide range of device thicknesses.iv ACKNOWLEDGEMENTS

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Optical mapping of large area thin film solar cells

Cited by 9 publications

References 8 publications

Spectroscopic ellipsometry: metrology for photovoltaics from the nanoscale to gigawatts

Spectroscopic ellipsometry: metrology for photovoltaics from the nanoscale to gigawatts

Through-the-glass spectroscopic ellipsometry of superstrate solar cells and large area panels

Optical measurement techniques for in-line process control in CdS/CdTe solar cell manufacturing

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