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Sodium doping of solution‐processed amine‐thiol based CIGS solar cells by thermal evaporation of NaCl

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journal contribution
posted on 12.03.2021, 12:09 by Sona Ulicna, Liam Welch, Ali Abbas, Mustafa Togay, Vincent Tsai, Tom Betts, Andrei Malkov, Michael Walls, Jake Bowers
Poor crystallinity, high degree of porosity and rough surfaces are the main drawbacks of solution-processed CIGS absorbers resulting in lower power conversion efficiencies when compared to vacuum-based CIGS solar cells. Therefore, promoting absorber grain growth is key to further improve solution-based solar cell performance. The effect of alkali elements such as Na in CIGS absorbers is generally recognised to have beneficial effects not only on the absorber opto-electronic properties but also on the grain growth. In this work, thermal evaporation of a thin layer of NaCl prior to selenisation resulted in absorbers with significantly larger CIGS grains than previously seen with Na diffusing directly from the from soda-lime glass substrate. NaCl is non-toxic, abundant and readily available compound that has not been typically used as an evaporation source, but rather as an additive into CIGS precursor solution. The effect of Na on these solution-processed CIGS devices was primarily observed in the spectacular morphological changes leading to improved carrier collection and minority carrier lifetimes, but less on the absorber doping. Transmission electron microscopy (TEM) revealed voids forming around large CIGS grains upon NaCl addition and these had a negative effect on inter-grain carrier transport. Nonetheless, the resulting device performance doubled from 5% to 10% with addition of Na using this doping approach; however, a compromise between the optimum grain growth and optimum electronic properties had to be made. This study demonstrates a novel, simple and effective Na-doping strategy for CIGS absorbers and reveals the current limitations of the Na-doping in solution-processed atmospherically deposited cells.

Funding

Solution processed CIGS thin film solar cells from metal chalcogenide precursors

Engineering and Physical Sciences Research Council

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History

School

  • Mechanical, Electrical and Manufacturing Engineering
  • Science

Department

  • Chemistry

Research Unit

  • Centre for Renewable Energy Systems Technology (CREST)

Published in

Progress in Photovoltaics: Research and Applications

Publisher

Wiley

Version

VoR (Version of Record)

Rights holder

© The authors

Publisher statement

This is an Open Access Article. It is published by Wiley under the Creative Commons Attribution 4.0 Unported Licence (CC BY). Full details of this licence are available at: http://creativecommons.org/licenses/by/4.0/

Acceptance date

23/02/2021

Publication date

2021-03-09

ISSN

1062-7995

eISSN

1099-159X

Language

en

Depositor

Prof Andrei Malkov. Deposit date: 11 March 2021

Article number

pip.3408

Licence

Exports