Publications

2017 07 Electronic Materials Conference

HPY Publications

Dean’s EMC conference paper is accepted for a platform presentation at the 59th EMC Conference (June 28-30, 2017; University of Notre Dame, South Bend, ID).

2017 07 * Dean gives a presentation at the International Conference (EMC).

Heterojunction Electronic Properties and Compositional Differences of CdCl2 Post-Treated CdTe Solar Cell (Dean Collett 1, Jeffery A. Aguiar 2,3, Brian v. Devener 4, Yohan Yoon 5,6, Paul Haney 6, Nikolai Zhitenev 6, Michael Scarpulla 1,3, Prakash Koirala 7, Robert W. Collins 7 and Heayoung Yoon 1).

1. Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah.
2. Fuel Design and Development Department, Idaho National Laboratory, Idaho Falls, Idaho.
3. Department of Materials Science and Engineering, University of Utah, Salt Lake City, Utah.
4. Utah Nanofab, University of Utah, Salt Lake City, Utah.
5. Maryland NanoCenter, University of Maryland, College Park, Maryland.
6. Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland.
7. Department of Physics and Astronomy, Center for Photovoltaics Innovation and Commercialization, University of Toledo, Toledo, Ohio

2017 Nanoscale

HPY News, Publications

“Nanoscale imaging and spectroscopy of band gap and defects in polycrystalline photovoltaic devices”, Y. Yoon1, 2, J. Chae1, 2, A. M. Katzenmeyer1, H. P. Yoon1,2,3, J. Schumacher1, S. An1, A. Centronea1, and  N. Zhitenev1, Nanoscale 9, 7771, 2017.

1. Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA;
2. Maryland Nanocenter, College Park, Maryland 02421, USA;
3. Dept. of Electrical & Computer Engineering, University of Utah, Salt Lake City, Utah 84112, USA.

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2017 Sustainable Energy & Fuels

HPY News, Publications

“Deconvoluting the influences of 3D structure on the performance of photoelectrodes for solar-driven water splitting”, D. Esposito1,2, Y. Lee1,3, H. Yoon1,3, P. Haney1, N. Labrador2, T. Moffat1, A. Talin4, and  V. Szalai1, Sustainable Energy Fuels 1, 154, 2017.
1. Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA;
2. Department of Chemical Engineering, New York, New York 10027, USA;
3. Maryland Nanocenter, College Park, Maryland 02421, USA;
4. Sandia National Laboratories, Livermore, California 94551, USA

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2016 J. of Applied Physics

HPY Publications

“Depletion region surface effects in electron beam induced current measurements”, P. M. Haney, H. P. Yoon, B. Gaury, and N. B. Zhitenev , J. of Appl. Phys. 120, 105095702, 2016.

1. Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA; 2. Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah 84112, USA; 3. Maryland NanoCenter, University of Maryland, College Park, Maryland 20742.

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2016 Electronic Materials Conference

HPY Publications

“Imaging Local Optoelectronic Properties of Polycrystalline CdTe Solar Cells”, H. Yoon , Y. Yoon, P. Haney, S. An, P. Koirala, R. Collins, J. Chae, A. Katzenmeyer, A. Centrone and N. Zhitenev, presented by H. Yoon at the Electronic Materials Conference in Newark, DE, June 2016.

1. Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah, USA.
2. Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland, USA.
3. Maryland NanoCenter, University of Maryland, College Park, Maryland, USA.
4. Physics and Astronomy, University of Toledo, Toledo, Ohio, USA; 5. Sandia National Laboratories, Albuquerque, New Mexico, USA

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2015 European PV Solar Energy Conference and Exhibition

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PTIR“Local measurement of photocurrent and band gap in CdTe solar cells”, Y. Yoon, J. Chae, A. Katzenmeyer, H. Yoon, J. Schumacher, S. An, A. Centrone, N. Zhitenev, 31st European Photovoltaic Solar Energy Conference and Exhibition, p. 1243, 2015. (DOI: 10.4229/EUPVSEC20152015-3DV.1.34)

1. Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland, 20899, USA.
2. Maryland Nanocenter, University of Maryland, College Park, Maryland, 20742, USA

 

ABSTRACT. Polycrystalline thin film technology has shown great promise for low cost, high efficiency photovoltaics. To further increase the power efficiency, a firm understanding of microstructural properties of the devices is required. In this work, we investigate the inhomogeneous electrical and optical properties using local excitation techniques that generate excess carriers by a near-field light illumination or by a focused electron beam irradiation. The spatially resolved photocurrent images of n-CdS / p-CdTe devices obtained by both techniques show high carrier collection efficiencies at grain boundaries. A novel and complementary technique, photothermal induced resonance (PTIR), is also used to obtain absorption spectra and maps in the near-field over a broad range of wavelengths. In PTIR a wavelength tunable pulsed laser is used in combination with an atomic force microscope tip to detect the local thermal expansion induced by light absorption. Sub-micrometer thick lamella samples of CdTe solar cells are measured, and the variation of local band-gap is analyzed. We discuss the resolution and the sensitivity of the techniques in the range of photon energies close to the band gap.

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2015 Nanotechnology

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Paul_Nanotechnology“Electron beam induced current in the high injection regime”, P. M. Haney, H. P. Yoon, P. Koirala, R. W. Collins, and N. B. Zhitenev, Nanotechnology 26, 295401, 2015.

1. Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
2. Maryland NanoCenter, University of Maryland, College Park, MD 20742.
3. Dept. of Physics and Astronomy, University of Toledo, Toledo, OH, 43606.

ABSTRACT. Electron beam induced current (EBIC) is a powerful technique which measures the charge collection efficiency of photovoltaics with sub-micron spatial resolution. The exciting electron beam results in a high generation rate density of electron–hole pairs, which may drive the system into nonlinear regimes. An analytic model is presented which describes the EBIC response when the total electron–hole pair generation rate exceeds the rate at which carriers are extracted by the photovoltaic cell, and charge accumulation and screening occur. The model provides a simple estimate of the onset of the high injection regime in terms of the material resistivity and thickness, and provides a straightforward way to predict the EBIC lineshape in the high injection regime. The model is verified by comparing its predictions to numerical simulations in one- and two-dimensions. Features of the experimental data, such as the magnitude and position of maximum collection efficiency versus electron beam current, are consistent with the  three dimensional model.

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2015 IEEE Photovoltaic Specialists Conference

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pvsc_2015_poster“Local Photocarrier Dynamics in CdTe Solar Cells Under Optical and Electron Beam Excitations”, H. P. Yoon, P. M. Haney, Y. Yoon, S. An, J. I. Basham, and N. B. Zhitenev, 42th IEEE Photovoltaic Specialists Conference, p. 1, 2015. (DOI: 10.1109/PVSC.2015.7356020)

1. Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland, 20899, USA.
2. Maryland Nanocenter, University of Maryland, College Park, Maryland, 20742, USA

ABSTRACT. We compare local carrier dynamics in n-CdS / p-CdTe solar cells, where the electron-hole pairs are generated by either near-field optical illumination or highly focused electron beam excitation. An ion beam milling process was used to prepare a smooth surface of cross-sectional devices. The spatially resolved photocurrent images confirm high carrier collection efficiency at grain boundaries. An analytical model was used to extract material parameters at the level of single grains. We find that the minority carrier diffusion lengths extracted from both local measurement techniques are in excellent agreement, but are smaller than the values determined from macro-scale measurements.

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