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Title: Charge transport in CdTe solar cells revealed by conductive tomographic atomic force microscopy

Abstract

Polycrystalline photovoltaics comprising cadmium telluride (CdTe) represent a growing portion of the solar cell market, yet the physical picture of charge transport through the meso-scale grain morphology remains a topic of debate. It is unknown how thin film morphology affects the transport of electron-hole pairs. Accordingly this study is the first to generate three dimensional images of photocurrent throughout a thin-film solar cell, revealing the profound influence of grain boundaries and stacking faults on device efficiency.

Authors:
 [1];  [1];  [2];  [3]; ORCiD logo [3]; ORCiD logo [1]
  1. Univ. of Connecticut, Storrs, CT (United States). Inst. of Materials Science
  2. Colorado State Univ., Fort Collins, CO (United States)
  3. Brookhaven National Lab. (BNL), Upton, NY (United States). Center for Functional Nanomaterials (CFN)
Publication Date:
Research Org.:
Brookhaven National Lab. (BNL), Upton, NY (United States). Center for Functional Nanomaterials (CFN)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1361263
Report Number(s):
BNL-113894-2017-JA
Journal ID: ISSN 2058-7546; R&D Project: 16060; 16060; KC0403020
Grant/Contract Number:
SC0012704
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nature Energy
Additional Journal Information:
Journal Volume: 1; Journal Issue: 11; Journal ID: ISSN 2058-7546
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; Charge Transport; CdTe solar cells; tomographic atomic force microscopy; Transmission Electron Microscopy; Center for Functional Nanomaterials

Citation Formats

Luria, Justin, Kutes, Yasemin, Moore, Andrew, Zhang, Lihua, Stach, Eric A., and Huey, Bryan D.. Charge transport in CdTe solar cells revealed by conductive tomographic atomic force microscopy. United States: N. p., 2016. Web. doi:10.1038/nenergy.2016.150.
Luria, Justin, Kutes, Yasemin, Moore, Andrew, Zhang, Lihua, Stach, Eric A., & Huey, Bryan D.. Charge transport in CdTe solar cells revealed by conductive tomographic atomic force microscopy. United States. doi:10.1038/nenergy.2016.150.
Luria, Justin, Kutes, Yasemin, Moore, Andrew, Zhang, Lihua, Stach, Eric A., and Huey, Bryan D.. 2016. "Charge transport in CdTe solar cells revealed by conductive tomographic atomic force microscopy". United States. doi:10.1038/nenergy.2016.150. https://www.osti.gov/servlets/purl/1361263.
@article{osti_1361263,
title = {Charge transport in CdTe solar cells revealed by conductive tomographic atomic force microscopy},
author = {Luria, Justin and Kutes, Yasemin and Moore, Andrew and Zhang, Lihua and Stach, Eric A. and Huey, Bryan D.},
abstractNote = {Polycrystalline photovoltaics comprising cadmium telluride (CdTe) represent a growing portion of the solar cell market, yet the physical picture of charge transport through the meso-scale grain morphology remains a topic of debate. It is unknown how thin film morphology affects the transport of electron-hole pairs. Accordingly this study is the first to generate three dimensional images of photocurrent throughout a thin-film solar cell, revealing the profound influence of grain boundaries and stacking faults on device efficiency.},
doi = {10.1038/nenergy.2016.150},
journal = {Nature Energy},
number = 11,
volume = 1,
place = {United States},
year = 2016,
month = 9
}

Journal Article:
Free Publicly Available Full Text
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  • No abstract prepared.
  • We investigated the effects of the etching processes using bromine and nitric-phosphoric acid solutions, as well as of Cu, in the bulk electrical conductivity of CdTe/CdS solar cells using conductive atomic force microscopy (C-AFM). Although the etching process can create a conductive layer on the surface of the CdTe, the layer is very shallow. In contrast, the addition of a thin layer of Cu to the surface creates a conductive layer inside the CdTe that is not uniform in depth, is concentrated at grains boundaries, and may short circuit the device if the CdTe is too thin. The etching processmore » facilitates the Cu diffusion and results in thicker conductive layers. The existence of this inhomogeneous conductive layer directly affects the current transport and is probably the reason for needing thick CdTe in these devices.« less
  • We investigated the effects of the etching processes using bromine and nitric-phosphoric acid solutions, as well as of Cu, in the bulk electrical conductivity of CdTe/CdS solar cells using conductive atomic force microscopy (C-AFM). Although the etching process can create a conductive layer on the surface of the CdTe, the layer is very shallow. In contrast, the addition of a thin layer of Cu to the surface creates a conductive layer inside the CdTe that is not uniform in depth, is concentrated at grains boundaries, and may short circuit the device if the CdTe is too thin. The etching processmore » facilitates the Cu diffusion and results in thicker conductive layers. The existence of this inhomogeneous conductive layer directly affects the current transport and is probably the reason for needing thick CdTe in these devices.« less
  • In this work we describe for the first time the use of conductive atomic force microscopy (C-AFM) in the study of CdTe/CdS solar cells, before and after the etching processes used in device fabrication. C-AFM is a new technique that provides information on the electrical properties of the sample in conjunction with topographic images with high lateral resolution. At the same time, this technique allows for the generation of I-V curves at very well-defined locations. A potential is applied between the sample and a very sharp tip, which scans the sample in contact mode. The current images showed that differentmore » CdTe grains produce different contrast. Etching the CdTe with a bromine/methanol solution enhanced the current along grains boundaries when compared to the intragrain material. Etching with a solution of nitric and phosphoric acids did not show this effect. Instead, it increased the current through the whole sample surface.« less