Hole transport in porphyrin thin films

Abstract

Hole transport in p-type organic semiconductors is a key issue in the development of organic electronic devices. Here the diffusion of holes in porphyrin thin films is investigated. Smooth anatase TiO 2 films are coated with an amorphous thin film of zinc-tetra͑4-carboxyphenyl͒ porphyrin ͑ZnTCPP͒ molecules acting as sensitizer. Optical excitation of the porphyrin stimulates the injection of electrons into the conduction band of TiO 2 . The remaining holes migrate towards the back electrode where they are collected. Current-voltage and capacitance-voltage analysis reveal that the TiO 2 / ZnTCPP system can be regarded as an n-p heterojunction, with a donor density of N D ϭ2.

Vibrationally Resolved Fluorescence from Organic Molecules near Metal Surfaces in a Scanning Tunneling Microscope

“…The generation of STM-induced molecular fluorescence from H 2 TBPP appears related to its hole-transport character typical of aromatic-amine compounds [26,28]. STM-induced molecular fluorescence was not observed for a similar multimonolayer of electron-transport tris-(8-hydroxyquinoline) aluminium molecules.…”

“…However, for energy forbidden transitions, the mechanism of its occurrence is still not clear and awaits further experimental and theoretical studies. Possible causes may pertain to thermally assisted tunneling injection of holes via energetically distributed hole traps above HOMO [25,26] or energy level shifts due to charging of molecules [24]. The two-electron excitation mechanism proposed for Na overlayers on Cu(111) [27] is probably unlikely in the present case because the ''forbidden'' transitions were observed at very low currents.…”

Porphyrin dimers: A theoretical understanding of the impact of electronic coupling strength on the two-photon absorption properties

“…Organic compounds with large two-photon absorption (TPA) cross-sections, d, are of general interest due to their possible exploitation in optical devices, micro-or nano-fabrication, or bioimaging. [1][2][3][4][5][6][7] Porphyrins represent an important class of organic systems which, in addition to their biological functions, have been considered as sensitizers in photovoltaic cells, 8,9 holetransporting semiconductors, 10 optical limiters, 11 or components in artificial photosynthesis 12 or molecular-scale electronics, 13 due to their attractive spectroscopic and photophysical properties. Recently, a number of butadiyne-linked and other porphyrin oligomers have been shown to possess large third-order molecular polarizabilities and TPA cross-sections.…”

Photoresponsive Porphyrin Nanotubes of Meso-tetra(4-Sulfonatophenyl)Porphyrin and Sn(IV) meso-tetra(4-pyridyl)porphyrin

“…Both the dark current and photoconductance of the H 4 TPPS42--SnTPyP 4+ nanorods increased in case of exposure to iodine vapor, Figure 10C. The photocurrents of porphyrin films pretreated with iodine or oxygen electron acceptors were found to be higher than those without pretreatment (Yamashita and Maenobe, 1980; Hoffman and Ibers, 1983; Zhang et al, 1995; Savenije and Goossens, 2001). The contribution of acceptor impurities, e.g., O 2 or iodine, should be taken into account in the exciton mechanism of the photoconductance of porphyrins, where a charge-transfer complex formation with an acceptor such as iodine (Hoffman and Ibers, 1983) or oxygen (Kobayashi et al, 1993) was proposed.…”