Large work function shift of organic semiconductors inducing enhanced interfacial electron transfer in organic optoelectronics enabled by porphyrin aggregated nanostructures

• Published in: Nano research 2014-05, Vol.7 (5), p.679-693
• Main Authors: Vasilopoulou, Maria, Douvas, Antonios M., Georgiadou, Dimitra G., Constantoudis, Vassilios, Davazoglou, Dimitris, Kennou, Stella, Palilis, Leonidas C., Daphnomili, Dimitra, Coutsolelos, Athanassios G., Argitis, Panagiotis
• Format: Article
• Language: English
• Subjects: Aluminum; Atomic/Molecular Structure and Spectra; Biomedicine; Biotechnology; Cathodes; Chemistry and Materials Science; Chloride; Chlorides; Condensed Matter Physics; Devices; Efficiency; Electrons; Materials Science; Nanostructure; Nanotechnology; Organic light emitting diodes; Orientation; Photovoltaics; Porphyrins; Research Article; Semiconductors; Work functions
• ISSN: 1998-0124; 1998-0000
• DOI: 10.1007/s12274-014-0428-9

We report on large work function shifts induced by the coverage of several organic semiconducting (OSC) films commonly used in organic light emitting diodes (OLEDs) and organic photovoltaics (OPVs) with a porphyrin aggregated layer. The insertion between the organic film and the aluminum cathode of an aggregated layer based on the meso-tetrakis(1-methylpyridinium-4-yl) porphyrin chloride (porphyrin 1 ), with its molecules adopting a face-to-face orientation parallel to the organic substrate, results in a significant shift of the OSC work function towards lower values due to the formation of a large interfacial dipole and induces large enhancement of either the OLED or OPV device efficiency. OLEDs based on poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-2,1′,3-thiadiazole)] (F8BT) and incorporating the porphyrin 1 at the cathode interface exhibited current efficiency values up to 13.8 cd/A, an almost three-fold improvement over the efficiency of 4.5 cd/A of the reference device. Accordingly, OPVs based on poly(3-hexylthiophene) (P3HT), [6,6]-phenyl-C 61 butyric acid methyl ester (PC 61 BM) and porphyrin 1 increased their external quantum efficiencies to 4.4% relative to 2.7% for the reference device without the porphyrin layer. The incorporation of a layer based on the zinc meso-tetrakis (1-methylpyridinium-4-yl)porphyrin chloride (porphyrin 2 ), with its molecules adopting an edge-to-edge orientation, also introduced improvements, albeit more modest in all cases, highlighting the impact of molecular orientation.