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Atomic Force Photovoltaic Microscopy

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Performance of OPV devices is generally characterized by the power conversion efficiency. However this does not provide insight into local photocurrent spatial variations within these devices. Bulk-heterojunction (BHJ) devices may exhibit local efficiency variations from defects or the phase-separated nature of the microstructure as established by SEM TEM and other methods. Correlations between electrical properties and morphology in OPV films have been demonstrated by the scanning probe techniques time resolved electrostatic force microscopy (trEFM) and photoconductive AFM (pcAFM). However only photovoltaic films are characterized by these techniques.This invention provides methods for quantitative characterization of variations in fully operational photovoltaic devices by scanning across an array of solar cells that include the metal cathodes. The AFPM affords standard photovoltaic figures of merit near actual operating conditions and minimizes substrate-cAFM tip contact effects. AFPM was applied to elucidate variations within the BHJ organic solar cells of poly3-hexylthiophene (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM).

Benefits:

Unlike techniques that characterize only photovoltaic films AFPM examines functioning photovoltaic devices providing standard figures of merit such as power conversion efficiency. The flexibility of AFPM suggests applicability to nanoscale characterization of a wide range of opto-electronic materials and devices.

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