The nanoscale distribution of copper and its influence on charge collection in CdTe solar cells

Trumann Walker, Michael E. Stuckelberger, Tara Nietzold, Niranjana Mohan-Kumar, Christina Ossig, Maik Kahnt, Felix Wittwer, Barry Lai, Damien Salomon, Eric Colegrove, Mariana I. Bertoni

Research output: Contribution to journalArticlepeer-review

Abstract

For decades, Cu has been the primary dopant in CdTe photovoltaic absorbers. Typically, Cu acceptor concentrations in these devices are on the order of 1 × 1014 cm−3, which has made it notoriously difficult to directly correlate nanoscale Cu distributions to the local charge transport properties of these devices. To measure and correlate these properties, measurement techniques require high sensitivity to elemental concentration, large penetration depth, and operando compatibility. Techniques such as secondary-ion mass spectroscopy and X-ray energy dispersive spectroscopy are widely adopted to measure Cu concentrations, but they are limited by penetration depth, sensitivity, or spatial resolution. Additionally, they lack the operando capabilities required to correlate one-to-one Cu concentrations to electrical performance. In this work, correlative X-ray microscopy is used to investigate the spatial distribution of Cu and its impact on charge collection through the depth and breadth of CdTe photovoltaic devices. Plan-view, nanoscale X-ray fluorescence maps clearly demonstrate the spatial segregation of copper around regions thought to be CdTe grain boundaries. Complementary cross-section imaging unveils the transition of the maximum charge-collection efficiency from the ZnTe–CdTe interface to the CdS–CdTe interface as a function of Cu incorporation. The copper concentration through the depth of the CdTe layer is characterized by slow and fast diffusion components, and cross-section charge-transport modeling shows that the experimentally obtained charge collection can be explained by the modeled acceptor distribution through the depth of the CdTe layer.

Original languageEnglish (US)
Article number106595
JournalNano Energy
Volume91
DOIs
StatePublished - Jan 2022

Keywords

  • CdTe doping
  • Charge collection
  • Copper diffusion
  • X-ray beam induced current
  • X-ray fluorescence

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Materials Science(all)
  • Electrical and Electronic Engineering

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