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Wet chemical etching of cadmium telluride photovoltaics for enhanced open-circuit voltage, fill factor, and power conversion efficiency

Published online by Cambridge University Press:  09 December 2019

Ebin Bastola Open the ORCID record for Ebin Bastola [Opens in a new window] ,
Fadhil K. Alfadhili ,
Adam B. Phillips ,
Michael J. Heben  and
Randy J. Ellingson
Ebin Bastola
Affiliation:
Wright Center for Photovoltaics Innovation and Commercialization (PVIC), Department of Physics and Astronomy, University of Toledo, Toledo, Ohio 43606, USA
Fadhil K. Alfadhili
Affiliation:
Wright Center for Photovoltaics Innovation and Commercialization (PVIC), Department of Physics and Astronomy, University of Toledo, Toledo, Ohio 43606, USA
Adam B. Phillips
Affiliation:
Wright Center for Photovoltaics Innovation and Commercialization (PVIC), Department of Physics and Astronomy, University of Toledo, Toledo, Ohio 43606, USA
Michael J. Heben
Affiliation:
Wright Center for Photovoltaics Innovation and Commercialization (PVIC), Department of Physics and Astronomy, University of Toledo, Toledo, Ohio 43606, USA
Randy J. Ellingson*
Affiliation:
Wright Center for Photovoltaics Innovation and Commercialization (PVIC), Department of Physics and Astronomy, University of Toledo, Toledo, Ohio 43606, USA
*
a)Address all correspondence to this author. e-mail: Randy.Ellingson@utoledo.edu
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Abstract

Cadmium telluride (CdTe) is one of the leading photovoltaic technologies with a market share of around 5%. However, there still exist challenges to fabricate a rear contact for efficient transport of photogenerated holes. Here, etching effects of various iodine compounds including elemental iodine (I2), ammonium iodide (NH4I), mixture of elemental iodine and NH4I (I−/I3− etching), and formamidinium iodide were investigated. The treated CdTe surfaces were investigated using Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The CdTe devices were completed with or without treatments and tested under simulated AM1.5G solar spectrum to find photoconversion efficiency (PCE). Based on Raman spectra, XRD patterns, and surface morphology, it was shown that treatment with iodine compounds produced Te-rich surface on CdTe films, and temperature-dependent current–voltage characteristics showed reduced back barrier heights, which are essential for the formation of ohmic contact and reduce contact resistance. Based on current–voltage characteristics, the treatment enhanced open-circuit voltage (VOC) up to 841 mV, fill factor (FF) up to 78.2%, and PCE up to 14.0% compared with standard untreated CdTe devices (VOC ∼ 814 mV, FF ∼ 74%, and PCE ∼ 12.7%) with copper/gold back contact.

Keywords

photovoltaicsthin filmenergy generation

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Type
Invited Paper
Information
Journal of Materials Research , Volume 34 , Issue 24 , 30 December 2019 , pp. 3988 - 3997
Copyright
Copyright © Materials Research Society 2019 

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