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Title: Ion-damage-free planarization or shallow angle sectioning of solar cells for mapping grain orientation and nanoscale photovoltaic properties

Ion beam milling is the most common modern method for preparing specific features for microscopic analysis, even though concomitant ion implantation and amorphization remain persistent challenges, particularly as they often modify materials properties of interest. Atomic force microscopy (AFM), on the other hand, can mechanically mill specific nanoscale regions in plan-view without chemical or high energy ion damage, due to its resolution, directionality, and fine load control. As an example, AFM-nanomilling (AFM-NM) is implemented for top-down planarization of polycrystalline CdTe thin film solar cells, with a resulting decrease in the root mean square (RMS) roughness by an order of magnitude, even better than for a low incidence FIB polished surface. Subsequently AFM-based property maps reveal a substantially stronger contrast, in this case of the short-circuit current or open circuit voltage during light exposure. Furthermore, electron back scattering diffraction (EBSD) imaging also becomes possible upon AFM-NM, enabling direct correlations between the local materials properties and the polycrystalline microstructure. Smooth shallow-angle cross-sections are demonstrated as well, based on targeted oblique milling. As expected, this reveals a gradual decrease in the average short-circuit current and maximum power as the underlying CdS and electrode layers are approached, but a relatively consistent open-circuit voltage throughmore » the diminishing thickness of the CdTe absorber. AFM-based nanomilling is therefore a powerful tool for material characterization, uniquely providing ion-damage free, selective area, planar smoothing or low-angle sectioning of specimens while preserving their functionality. This then enables novel, co-located advanced AFM measurements, EBSD analysis, and investigations by related techniques that are otherwise hindered by surface morphology or surface damage.« less
Authors:
 [1] ;  [1] ;  [1] ;  [2] ;  [3] ;  [4] ;  [1] ;  [5] ;  [1]
  1. Univ. of Connecticut, Storrs, CT (United States). Dept. of Materials Science and Engineering
  2. Colorado State Univ., Fort Collins, CO (United States). Dept. of Physics
  3. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Applied Nuclear Technologies
  4. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Materials Characterization Dept.
  5. Univ. of Texas, El Paso, TX (United States). Dept. of Electrical and Computer Engineering
Publication Date:
Report Number(s):
SAND2016-12923J
Journal ID: ISSN 0957-4484; 650119
Grant/Contract Number:
AC04-94AL85000; SC0005037
Type:
Accepted Manuscript
Journal Name:
Nanotechnology
Additional Journal Information:
Journal Volume: 28; Journal Issue: 18; Journal ID: ISSN 0957-4484
Publisher:
IOP Publishing
Research Org:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
33 ADVANCED PROPULSION SYSTEMS; 77 NANOSCIENCE AND NANOTECHNOLOGY
OSTI Identifier:
1399879