Electric-field controlled light-emissive characteristics in nanoscale for polymer/fullerene organic solar cells

Bulk-hetero-junction (BHJ) organic photovoltaic cells (OPVCs) consisting of a poly(3-hexylthiophene) (P3HT) as a donor and 6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) as an acceptor were fabricated and their light-emissive characteristics as a function of applied bias were investigated. The nanoscale luminescence spectra at different positions on the P3HT/PCBM based photovoltaic cells were measured using a laser confocal microscope (LCM) with a high spatial resolution. For the P3HT/PCBM OPVCs with a relatively thin active layer, the light-emissive characteristics were changed considerably with varying applied bias. We observed that the luminescence intensity increased with increasing reverse bias under light illumination, this result was confirmed by the LCM photoluminescence mapping images. This result originates from the increase of free charges due to the de-trapping effect of trapped charge transfer excitons near the interface, through the external electric-field and incident light.