Mapping Shunting Paths at the Surface of Cu2ZnSn(S,Se)4 Films via Energy-Filtered Photoemission Microscopy

Devendra Tiwari; Mattia Cattelan; Robert L Harniman; Andrei Sarua; Ali Abbas; Jake W Bowers; Neil A Fox; David J Fermin

doi:10.1016/j.isci.2018.10.004

Mapping Shunting Paths at the Surface of Cu₂ZnSn(S,Se)₄ Films via Energy-Filtered Photoemission Microscopy

iScience. 2018 Nov 30:9:36-46. doi: 10.1016/j.isci.2018.10.004. Epub 2018 Oct 13.

Authors

Devendra Tiwari¹, Mattia Cattelan¹, Robert L Harniman¹, Andrei Sarua², Ali Abbas³, Jake W Bowers³, Neil A Fox⁴, David J Fermin⁵

Affiliations

¹ School of Chemistry, University of Bristol, Bristol BS8 1TS, UK.
² H H Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, UK.
³ Centre for Renewable Energy Systems Technology (CREST), Wolfson School of Mechanical, Electrical and Manufacturing Engineering, Loughborough University, Loughborough LE11 3TU, UK.
⁴ School of Chemistry, University of Bristol, Bristol BS8 1TS, UK; H H Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, UK.
⁵ School of Chemistry, University of Bristol, Bristol BS8 1TS, UK. Electronic address: david.fermin@bristol.ac.uk.

Abstract

The performance of Cu₂ZnSn(S,Se)₄ thin-film solar cells, commonly referred to as kesterite or CZTSSe, is limited by open-circuit voltage (V_OC) values less than 60% of the maximum theoretical limit. In the present study, we employ energy-filtered photoemission microscopy to visualize nanoscale shunting paths in solution-processed CZTSSe films, which limit the V_OC of cells to approximately 400 mV. These studies unveil areas of local effective work function (LEWF) narrowly distributed around 4.9 eV, whereas other portions show hotspots with LEWF as low as 4.2 eV. Localized valence band spectra and density functional theory calculations allow rationalizing the LEWF maps in terms of the CZTSSe effective work function broadened by potential energy fluctuations and nanoscale Sn(S,Se) phases.

Keywords: Chemistry; Energy Materials; Materials Science.