Partially interpenetrating heterojunction on bilayer photovoltaic devices of electrodeposited polythiophene/methanofullerene

Parent or unsubstituted polythiophene (PT) films electrodeposited on hole-extraction-layer-coated ITO electrodes were used as the donor material in bilayer organic photovoltaic (OPV) devices. The electrodeposited PT layers had a porous surface with numerous voids and hollows of nanometer dimensions. The acceptor, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), was deposited on the PT layer by spin-coating from chlorobenzene solutions. Cross-sectional STEM-EDS (scanning transmission electron microscopy combined with energy dispersive X-ray spectroscopy) analysis revealed that some of the PCBM molecules infiltrated into the PT layer to form a PT/PCBM interpenetrating layer 8–9 nm thick between homogeneous PT and PCBM layers. The PT-based OPV devices fabricated with an optimal PT layer thickness (20 nm) showed a power conversion efficiency of 1.5% under AM 1.5 G (100 mW/cm2) illumination, which is higher than that of previously reported OPV devices using electrodeposited polythiophenes in the active layer.