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CHARACTERIZATION OF A HIGHLY PHOTOACTIVE MOLECULAR SEMICONDUCTOR - OXOTITANIUM PHTHALOCYANINE
Ghosez, Philippe; COTE, R.; GASTONGUAY, L. et al.
1993In Chemistry of Materials, 5 (10), p. 1581-1590
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Abstract :
[en] Oxotitanium phthalocyanine (OTiPc) thin films have been sublimed at various thicknesses on SnO2 and glass substrates. The morphology, crystallinity, and photoelectrochemical activity of the films have been studied. It was found that the physical and photoelectrochemical properties of the films are greatly influenced by the temperature reached by the substrate during the sublimation. Below 80-degrees-C, amorphous films are obtained while the films are partially crystalline when the substrate is allowed to reach about 140-degrees-C. Amorphous films are made of tightly packed aggregates of circular section while partially crystalline films consists of platelets. All films are porous and permeable to the I3-/I- redox system. The dominant polymorph in partially crystalline films is not the same for all film thicknesses. It is phase IV OTiPc (as deduced by electron diffraction) for films thinner than about 2000 angstrom. On the other hand, for films thicker than about 8000 angstrom, phase I OTiPc becomes the dominant polymorph (as deduced by X-ray diffraction). It is replaced by phase II for 20 000-angstrom-thick films of OTiPc. Partially crystalline films are the only ones to absorb in the near-infrared (NIR) region. This typical absorption is going along with an improvement of the photoactivity of the films. In partially crystalline films, energy is transferred from the amorphous to the crystalline regions where most of the charges are generated. Quantum yields for electron collection per incident photon may reach over 25% in short circuit conditions, at 850 nm, the Q-band absorption maximum for 8000-angstrom-thick films. Those films are phase I OTiPc. Under 35 MW CM-2 polychromatic illumination, the same films are characterized by short circuit photocurrents of 1.5 mA cm-2. A NIR absorbance is an important factor required to obtain a high photoactivity, but it is not the only one. Interaction of OTiPc with oxygen at the purification level of the crude material is very important as well.
Disciplines :
Materials science & engineering
Author, co-author :
Ghosez, Philippe  ;  Université de Liège - ULiège > Département de physique > Physique théorique des matériaux
COTE, R.
GASTONGUAY, L.
VEILLEUX, G.
DENES, G.
DODELET, J. P.
Language :
English
Title :
CHARACTERIZATION OF A HIGHLY PHOTOACTIVE MOLECULAR SEMICONDUCTOR - OXOTITANIUM PHTHALOCYANINE
Publication date :
1993
Journal title :
Chemistry of Materials
ISSN :
0897-4756
eISSN :
1520-5002
Publisher :
American Chemical Society, Washington, United States - District of Columbia
Volume :
5
Issue :
10
Pages :
1581-1590
Peer reviewed :
Peer Reviewed verified by ORBi
Available on ORBi :
since 02 December 2009

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