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Title: Locating the electrical junctions in Cu(In,Ga)Se 2 and Cu 2ZnSnSe 4 solar cells by scanning capacitance spectroscopy

Here, we determined the electrical junction (EJ) locations in Cu(In,Ga)Se 2 (CIGS) and Cu 2ZnSnSe 4 (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 voltagemore » difference between CIGS and CZTS.« less
 [1] ;  [2] ;  [2] ;  [2] ;  [3] ;  [4] ;  [2]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States); Colorado School of Mines, Golden, CO (United States)
  2. National Renewable Energy Lab. (NREL), Golden, CO (United States)
  3. The Univ. of Toledo, Toledo OH (United States)
  4. Colorado School of Mines, Golden CO (United States)
Publication Date:
Report Number(s):
Journal ID: ISSN 1062-7995
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Progress in Photovoltaics
Additional Journal Information:
Journal Volume: 25; Journal Issue: 1; Journal ID: ISSN 1062-7995
Research Org:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
Country of Publication:
United States
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; electrical junction location; CIGS; CZTS; scanning capacitance spectroscopy; homojunction; heterointerface
OSTI Identifier: