Mapping photovoltaic performance with nanoscale resolution

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 42000 I/V curves spatially separated by similar to 5nm. For these CdTe/CdS microcells, the calculated photoconduction ranges from 0 to 700 picoSiemens (pS) upon illumination with similar to 1.6 suns, depending on location and biasing conditions. Mean short circuit currents of 2pA, maximum powers of 0.5pW, and fill factors of 30% are determined. The mean voltage at which the detected photocurrent is zero is determined to be 0.7V. 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 (c) 2015 John Wiley & Sons, Ltd.