Sensitization of organic photovoltaic cells based on interlayer excitation energy transfer

We incorporated an additional p-type organic semiconductor layer (APL) between the anode and the phthalocyanine layer, which is an indispensable p-type semiconductor layer (IPL) in forming a p/n junction with a fullerene C60 layer. We used two thiophene/phenylene co-oligomers as the APL. The incorporation increases the short-circuit current density (JSC) and enhances incident photon–current conversion efficiency (IPCE) over the wavelength region where the APL shows strong absorption. Combined dependence of the APL/IPL implies that Förster resonance excitation transfer is the main factor in JSC and IPCE enhancements. We demonstrate clearly that the ‘positive’ hole injection barrier at the interface between the APL and the IPL impacts the smooth transportation of holes to the indium-tin-oxide anode. However, the small positive hole barrier of 0.1 eV has no noticeable influence on the fill factor of the current density versus voltage characteristic under photoirradiation, or on those devices with ‘negative’ hole barriers.