Mapping photovoltaic performance with nanoscale resolution

• Published in: Progress in photovoltaics 2016-03, Vol.24 (3), p.315-325
• Main Authors: Kutes, Yasemin, Aguirre, Brandon A., Bosse, James L., Cruz-Campa, Jose L., Zubia, David, Huey, Bryan D.
• Format: Article
• Language: English
• Subjects: atomic force microscopy (AFM); Cadmium sulfides; Cadmium tellurides; CdTe; characterization; Illumination; Maximum power; nanoscale; Nanostructure; photovoltaic; Photovoltaic cells; Short circuit currents; Solar cells
• ISSN: 1062-7995; 1099-159X
• DOI: 10.1002/pip.2698

Photo‐conductive AFM spectroscopy (‘pcAFMs’) is proposed as a high‐resolution approach for investigating nanostructured photovoltaics, uniquely providing nanoscale maps of photovoltaic (PV) performance parameters such as the short circuit current, open circuit voltage, maximum power, or fill factor. The method is demonstrated with a stack of 21 images acquired during in situ illumination of micropatterned polycrystalline CdTe/CdS, providing more than 42 000 I/V curves spatially separated by ~5 nm. For these CdTe/CdS microcells, the calculated photoconduction ranges from 0 to 700 picoSiemens (pS) upon illumination with ~1.6 suns, depending on location and biasing conditions. Mean short circuit currents of 2 pA, maximum powers of 0.5 pW, and fill factors of 30% are determined. The mean voltage at which the detected photocurrent is zero is determined to be 0.7 V. Significantly, enhancements and reductions in these more commonly macroscopic PV performance metrics are observed to correlate with certain grains and grain boundaries, and are confirmed to be independent of topography. These results demonstrate the benefits of nanoscale resolved PV functional measurements, reiterate the importance of microstructural control down to the nanoscale for 'PV devices, and provide a widely applicable new approach for directly investigating PV materials. Copyright © 2015 John Wiley & Sons, Ltd. Photo‐conductive AFM spectroscopy (‘pcAFMs’) is proposed as a high‐resolution approach for investigating photovoltaics, uniquely providing nanoscale maps of photovoltaic (PV) performance metrics. The method is demonstrated on micropatterned polycrystalline CdTe/CdS solar cells. The calculated photoconduction ranges from 0 to 700 picoSiemens (pS) upon ~1.6 suns of in situ illumination, depending on location and biasing conditions. Mean short circuit currents of 2 pA, open circuit voltages of 0.8 V, maximum powers of 0.5 pW, and fill factors of 30% are determined.