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

Journal Article · 10 April 2017 · Nanotechnology

DOI: https://doi.org/10.1088/1361-6528/aa67c2 · OSTI ID:1399879

Kutes, Yasemin ^[1]; Luria, Justin ^[1]; Sun, Yu ^[1]; Moore, Andrew ^[2]; Aguirre, Brandon A. ^[3]; Cruz-Campa, Jose L. ^[4]; Aindow, Mark ^[1]; Zubia, David ^[5]; Huey, Bryan D. ^[1]

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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

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 through 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.

• Research Organization: Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC)
• Grant/Contract Number: AC04-94AL85000; SC0005037
• OSTI ID: 1399879
• Alternate ID(s): OSTI ID: 22843270
• Report Number(s): SAND2016--12923J; 650119
• Journal Information: Nanotechnology, Journal Name: Nanotechnology Journal Issue: 18 Vol. 28; ISSN 0957-4484
• Publisher: IOP PublishingCopyright Statement
• Country of Publication: United States
• Language: English