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203 results on '"Sampath, Walajabad"'

4. Local Electronic Structure Changes in Polycrystalline CdTe with CdCl$_2$ Treatment and Air Exposure

Author

Berg, Morgann, Kephart, Jason M., Munshi, Amit, Sampath, Walajabad S., Ohta, Taisuke, and Chan, Calvin

Subjects
Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics, Physics - Applied Physics, Physics - Chemical Physics, Physics - Instrumentation and Detectors
Abstract

Post-deposition CdCl$_2$ treatment of polycrystalline CdTe is known to increase photovoltaic efficiency. However, the precise chemical, structural, and electronic changes that underpin this improvement are still debated. In this study, spectroscopic photoemission electron microscopy was used to spatially map the vacuum level and ionization energy of CdTe films, enabling the identification of electronic structure variations between grains and grain boundaries. In vacuo preparation and inert transfer of oxide-free CdTe surfaces isolated the separate effects of CdCl$_2$ treatment and ambient oxygen exposure. Qualitatively, grain boundaries displayed lower work function and downward band bending relative to grain interiors, but only after air exposure of CdCl$_2$-treated CdTe. Analysis of numerous space charge regions at grain boundaries (GBs) showed an average depletion width of 290 nm and an average band bending magnitude of 70 meV, corresponding to a GB trap density of 10$^{11}$ cm$^{-2}$ and a net carrier density of 10$^{15}$ cm$^{-3}$. These results suggest that both CdCl$_2$ treatment and oxygen exposure may be independently tuned to enhance CdTe photovoltaic performance by engineering the interface and bulk electronic structure.

Published
2018
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6. Effects of CdCl$_2$ treatment on the local electronic properties of polycrystalline CdTe measured with photoemission electron microscopy

Author

Berg, Morgann, Kephart, Jason M., Sampath, Walajabad S., Ohta, Taisuke, and Chan, Calvin

Subjects
Condensed Matter - Materials Science, Physics - Applied Physics, Physics - Chemical Physics, Physics - Instrumentation and Detectors
Abstract

To investigate the effects of CdCl$_2$ treatment on the local electronic properties of polycrystalline CdTe films, we conducted a photoemission electron microscopy (PEEM) study of polished surfaces of CdTe films in superstrate configuration, with and without CdCl$_2$ treatment. From photoemission intensity images, we observed the tendency for individual exposed grain interiors to vary in photoemission intensity, regardless of whether or not films received CdCl$_2$ treatment. Additionally, grain boundaries develop contrast in photoemission intensity images different from grain interiors after an air exposure step, similar to observations of activated grain boundaries using scanning Kelvin probe force microscopy studies. These results suggest that work function varies locally, from one grain interior to another, as well as between grain boundaries and grain interiors., Comment: 5 pages, 3 figures, Photovoltaics Specialist Conference (PVSC), 2017

Published
2017

23. CdTe-based thin film photovoltaics: Recent advances, current challenges and future prospects

Author

Scarpulla, Michael A., primary, McCandless, Brian, additional, Phillips, Adam B., additional, Yan, Yanfa, additional, Heben, Michael J., additional, Wolden, Colin, additional, Xiong, Gang, additional, Metzger, Wyatt K., additional, Mao, Dan, additional, Krasikov, Dmitry, additional, Sankin, Igor, additional, Grover, Sachit, additional, Munshi, Amit, additional, Sampath, Walajabad, additional, Sites, James R., additional, Bothwell, Alexandra, additional, Albin, David, additional, Reese, Matthew O., additional, Romeo, Alessandro, additional, Nardone, Marco, additional, Klie, Robert, additional, Walls, J. Michael, additional, Fiducia, Thomas, additional, Abbas, Ali, additional, and Hayes, Sarah M., additional

Published
2023
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28. Quantitative Cathodoluminescence Mapping: A CdMgSeTe Thin-Film Case Study

Author

Torabi, Aida, primary, Sullivan, James, additional, Reich, Carey, additional, Wunch, Melissa A., additional, Garcia, Juan Alexandro, additional, Beck, Claudia, additional, Munshi, Amit H., additional, Shimpi, Tushar, additional, Roberts, Mienie, additional, Sampath, Walajabad, additional, and Harvey, Taylor B., additional

Published
2022
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30. Microscopy Visualization of Carrier Transport in CdSeTe/CdTe Solar Cells

Author

Xiao, Chuanxiao, primary, Jiang, Chun-Sheng, additional, Nardone, Marco, additional, Albin, David, additional, Danielson, Adam, additional, Munshi, Amit H., additional, Shimpi, Tushar, additional, Sampath, Walajabad, additional, Jones, Sean, additional, Al-Jassim, Mowafak M., additional, Teeter, Glenn, additional, Haegel, Nancy M., additional, and Moutinho, Helio R., additional

Published
2022
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31. Analysis of CdTe photovoltaic cells for ambient light energy harvesting

Author

Massachusetts Institute of Technology. Department of Mechanical Engineering, Mathews, Ian, Kantareddy, Sai Nithin R., Liu, Zhe, Munshi, Amit, Barth, Kurt, Sampath, Walajabad, Buonassisi, Tonio, Peters, Ian Marius, Massachusetts Institute of Technology. Department of Mechanical Engineering, Mathews, Ian, Kantareddy, Sai Nithin R., Liu, Zhe, Munshi, Amit, Barth, Kurt, Sampath, Walajabad, Buonassisi, Tonio, and Peters, Ian Marius

Abstract

© 2020 IOP Publishing Ltd. This paper investigates the suitability of CdTe photovoltaic cells to be used as power sources for wireless sensors located in buildings. We fabricate and test a CdTe photovoltaic cell with a transparent conducting oxide front contact that provides for high photocurrents and low series resistance at low light intensities and measures the photovoltaic response of this cell across five orders of magnitude of AM1.5G light intensity. Efficiencies of 10% and 17.1% are measured under ∼1 W m-2 AM1.5G and LED irradiance respectively, the highest values for a CdTe device under ambient lighting measured to date. We use our results to assess the potential of CdTe for internet of things devices from an optoelectronic, as well as a techno-economic perspective, considering its established manufacturing know-how, potential for low-cost, proven long-term stability and issues around the use of cadmium., U.S. Department of Energy (Award DE-EE0008177), (Awards 1540007 and 1538733)

Published
2022

36. Metastability and Degradation of CdTe Solar Cells Investigated by nm-Scale Electrical Potential Imaging

Author

Jiang, Chun-Sheng, primary, Albin, David, additional, Nardone, Marco, additional, Howard, Kassidy H., additional, Danielson, Adam, additional, Munshi, Amit, additional, Shimpi, Tushar, additional, Sampath, Walajabad, additional, Xiao, Chuanxiao, additional, Moutinho, Helio R., additional, Al-Jassim, Mowafak M., additional, and Teeter, Glenn, additional

Published
2022
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41. What limits the voltage of polycrystalline CdSeTe solar cells? Insights from spectrally resolved and quantitative photoluminescence

Author

Onno, Arthur L., primary, Reich, Carey L., additional, Li, Siming, additional, Danielson, Adam, additional, Weigand, William, additional, Bothwell, Alexandra, additional, Grover, Sachit, additional, Bailey, Jeff, additional, Xiong, Gang, additional, Kuciauskas, Darius, additional, Sampath, Walajabad, additional, and Holman, Zachary C., additional

Published
2022
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47. Analysis of CdTe photovoltaic cells for ambient light energy harvesting

Author

Mathews, Ian, Kantareddy, Sai Nithin Reddy, Liu, Zhe, Munshi, Amit, Barth, Kurt, Sampath, Walajabad, Buonassisi, Tonio, Peters, Ian Marius, Mathews, Ian, Kantareddy, Sai Nithin Reddy, Liu, Zhe, Munshi, Amit, Barth, Kurt, Sampath, Walajabad, Buonassisi, Tonio, and Peters, Ian Marius

Abstract

© 2020 IOP Publishing Ltd. This paper investigates the suitability of CdTe photovoltaic cells to be used as power sources for wireless sensors located in buildings. We fabricate and test a CdTe photovoltaic cell with a transparent conducting oxide front contact that provides for high photocurrents and low series resistance at low light intensities and measures the photovoltaic response of this cell across five orders of magnitude of AM1.5G light intensity. Efficiencies of 10% and 17.1% are measured under ∼1 W m-2 AM1.5G and LED irradiance respectively, the highest values for a CdTe device under ambient lighting measured to date. We use our results to assess the potential of CdTe for internet of things devices from an optoelectronic, as well as a techno-economic perspective, considering its established manufacturing know-how, potential for low-cost, proven long-term stability and issues around the use of cadmium.

Published
2021

49. Effect of chemical treatment on the optical properties of a cadmium telluride photovoltaic device investigated by spectroscopic ellipsometry

Author

Kohli, Sandeep, Manivannan, Venkatesan, Hilfiker, James N., McCurdy, Patrick R., Enzenroth, Robert A., Barth, Kurt L., Smith, Westcott P., Luebs, Richard, and Sampath, Walajabad S.

Subjects
Ellipsometry -- Research, Solar batteries -- Materials, Solar batteries -- Chemical properties, Solar cells -- Materials, Solar cells -- Chemical properties, Engineering and manufacturing industries, Environmental issues
Abstract

Spectroscopic ellipsometry has been successfully used to characterize the CdS/CdTe heterojunction solar cell deposited on TEC15 glass. The effects of copper treatment 077 the optical properties of a cadmium chloride treated photovoltaic device were investigated using ellipsometry. No changes in either the band gaps or critical points of CdTe layer were noticed as a result of copper treatment. The copper treated CdTe laver exhibited a higher refractive index in the visible and longer wavelengths ([less than or equal to]3 eV), as compared with the untreated layer. This was attributed to the increased disorder in the case of copper treated laver. [DOI: 10.1115/1.3097282]

Published
2009

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