Locating the Electrical Junctions in Cu(In,Ga)Se2 and Cu2ZnSnSe4 Solar Cells by Scanning Capacitance Spectroscopy

Chuanxiao Xiao, Chun Sheng Jiang, Helio Moutinho, Dean Levi, Yanfa Yan, Brian Gorman, Mowafak Al-Jassim

Research output: Contribution to journalArticlepeer-review

12 Scopus Citations


We determined the electrical junction (EJ) locations in Cu(In,Ga)Se2 (CIGS) and Cu2ZnSnSe4 (CZTS) solar cells with ~20-nm accuracy by developing scanning capacitance spectroscopy (SCS) applicable to the thin-film devices. Cross-sectional sample preparation for the SCS measurement was developed by high-energy ion milling at room temperature for polishing the cross section to make it flat, followed by low-energy ion milling at liquid nitrogen temperature for removing the damaged layer and subsequent annealing for growing a native oxide layer. The SCS shows distinct p-type, transitional, and n-type spectra across the devices, and the spectral features change rapidly with location in the depletion region, which results in determining the EJ with ~20-nm resolution. We found an n-type CIGS in the region next to the CIGS/CdS interface; thus, the cell is a homojunction. The EJ is ~40 nm from the interface on the CIGS side. In contrast, such an n-type CZTS was not found in the CZTS/CdS cells. The EJ is ~20 nm from the CZTS/CdS interface, which is consistent with asymmetrical carrier concentrations of the p-CZTS and n-CdS in a heterojunction cell. Our results of unambiguously determination of the junction locations contribute significantly to understanding the large open-circuit voltage difference between CIGS and CZTS.

Original languageAmerican English
Pages (from-to)33-40
Number of pages8
JournalProgress in Photovoltaics: Research and Applications
Issue number1
StatePublished - 2017

Bibliographical note

Publisher Copyright:
Copyright © 2016 John Wiley & Sons, Ltd.

NREL Publication Number

  • NREL/JA-5K00-65634


  • CIGS
  • CZTS
  • electrical junction location
  • heterointerface
  • homojunction
  • scanning capacitance spectroscopy


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