Variations in the Chemical and Electronic Impact of Post-Deposition Treatments on Cu(In,Ga)(S,Se)2 Absorbers
[1];
[3];
- Univ. of Nevada, Las Vegas, NV (United States)
- National Renewable Energy Lab. (NREL), Golden, CO (United States)
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS)
- Univ. of Nevada, Las Vegas, NV (United States); Karlsruhe Inst. of Technology (KIT) (Germany)
- STION Corp., San Jose, CA (United States)
We present a comparative study that focuses on the variability of post-deposition treatments (NaF-PDT and KF-PDT) and their impact on the chemical and electronic structure of chalcopyrite thin film solar cell absorbers. For this purpose, two 'extreme' chalcopyrite absorber systems are studied: Cu(In,Ga)(S,Se)2 with industrial relevance (STION), and Cu(In,Ga)Se2 with 'research grade' properties (NREL). Samples were subjected to NaF-PDT and KF-PDT, and investigated using x-ray and ultra-violet photoelectron spectroscopy, Auger electron spectroscopy, as well as synchrotron-based soft x-ray emission spectroscopy. Considerably different alkali-induced effects are found for the two systems. In particular, we only detect a PDT-related Cu depletion on the NREL absorber surfaces (and only on those leading to high-efficiency devices). We also observe a reduction in the surface S/Se ratio for all alkali-treated STION absorbers, in addition to the presence of sulfates after the KF-PDT. After processing the PDT absorbers to fully operating cells, we find that the PDT temperature has a significant impact on the resulting device efficiencies - both the NREL and STION absorbers can result in high-efficiency and low-efficiency devices, depending on KF-PDT processing parameters. The absorbers of low-efficiency KF-PDT devices show the largest Cu surface content after PDT, causing the valence band maximum to be closer to the Fermi energy, thus possibly leading to less efficient charge-carrier separation and/or enhanced recombination at the interface. Finally, we find varying degrees of Na, K, and/or F residuals on the different absorber surfaces after PDT, indicating a potential 'hidden' parameter in employing PDTs for improved solar cell performance.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); National Renewable Energy Lab. (NREL), Golden, CO (United States)
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Solar Energy Technologies Office; USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities Division
- Grant/Contract Number:
- AC02-05CH11231; AC36-08GO28308
- OSTI ID:
- 1594942
- Alternate ID(s):
- OSTI ID: 1576486
- Report Number(s):
- NREL/JA-5K00-75198; ark:/13030/qt9965x7nn
- Journal Information:
- ACS Applied Energy Materials, Vol. 2, Issue 2; ISSN 2574-0962
- Publisher:
- American Chemical Society (ACS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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