Interdigitated Bulk Heterojunction Organic Photovoltaic Cells With Aligned Copper Phthalocyanine Nanorods

We show that vertically aligned nanorod arrays composed of copper phthalocyanine (CuPc) molecules can be grown on various substrates using the oblique angle deposition technique in high vacuum. High-density nanorod arrays with diameters of 20-70 nm and spacing of 10-100 nm have been achieved with either stationary or rotated substrates. Scanning electron and atomic force microscopies are combined to study the morphology of CuPc nanorods grown under different conditions. X-ray diffraction reveals that the crystallinity of the CuPc nanorods is similar to a flat CuPc film deposited under normal molecular incidence. Interdigitated bulk heterojunctions (BHJs) have been formed by successfully infiltrating [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) to fill the spacing between the CuPc nanorods via spin coating. The resulted CuPc nanorod/PCBM photovoltaic cells possess a maximum power conversion efficiency approximately doubling that of bilayer CuPc/PCBM devices, demonstrating the effectiveness of the nanorod-based BHJ in enhancing both the donor-acceptor interfacial area and the exciton diffusion efficiency in the active layer.