Increasing the quantum efficiency of nickel phthalocyanine films by oxygen adsorption

Musser, M.; Dahlberg, S. C.

doi:10.1016/0039-6028(80)90426-4

Cited by 31 publications

(7 citation statements)

References 11 publications

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“…O 2 adsorbs weakly on Pcs. The resulting complex acts as a shallow electron trap which in the case of NiPc, for instance, can be removed by pumping. , Measurements on CuPc and H 2 Pc single crystals have shown that O 2 also reacts with paramagnetic defects (D) present in the crystals. The complex (D + O 2 - ) acts as a deep electron trap, releasing holes which become majority carriers .…”

Section: Resultsmentioning

confidence: 99%

Highly Photoactive Molecular Semiconductors: Determination of the Essential Parameters That Lead to an Improved Photoactivity for Modified Chloroaluminum Phthalocyanine Thin Films

et al. 1996

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Thin films of chloroaluminum, chlorogallium, and chloroindium phthalocyanines (ClAlPc, ClGaPc, and ClInPc) have been sublimed on SnO 2 substrates maintained during sublimation at temperatures ranging from -130 to 190°C. Using this procedure, it is possible to obtain molecular semiconductor layers with a structure varying from amorphous to polycrystalline. These layers were immersed in KI 3 /KI or KCl solutions at pH ) 3.0. This treatment was found to improve drastically the photoelectrochemical activity of ClAlPc thin films. Shortcircuit photocurrents J sc ) 0.75 ( 0.25 mA/cm 2 were obtained, using polychromatic illumination (35 mW/ cm 2 ), after immersion of ClAlPc into KCl solutions while lower J sc values (0.3 ( 0.1 mA/cm 2 ) were obtained for KI 3 /KI solutions. No change in the photoactivity was observed either for ClGaPc or for ClInPc when they were immersed in the same solutions. Both molecular semiconductors provided lower short-circuit photocurrents (J sc e 0.15 ( 0.03 mA/cm 2 for ClGaPc; J sc e 0.20 ( 0.02 mA/cm 2 for ClInPc). The characterization of the chloro-trivalent metal phthalocyanine films indicates that the hydrolysis of the metalCl bond is essential for the occurrence of the physicochemical transformation leading to improved photoactivity. The Al-Cl bond of ClAlPc hydrolyzes, but this reaction does not occur for ClGaPc or for ClInPc. In contact with KI 3 /KI or KCl solutions at pH ) 3.0, bulk hydrolysis occurs for ClAlPc, only if both H 3 O + and an anion could diffuse from the solution into the material. The large I 3 -anion is prevented from doing so for polycrystalline ClAlPc films obtained by sublimation on SnO 2 substrates maintained at 180°C. However, it can diffuse easily in more disorganized films obtained at lower substrate temperatures. Powders of the chlorotrivalent metal phthalocyanines as well as bromoaluminum phthalocyanine (BrAlPc) were used to quantify anion incorporation in these materials. After complete hydrolysis of BrAlPc (powder) and ClAlPc (films) there are ca. 50-85% of the anions, generated in situ by the hydrolysis reaction or diffusing from the solution as a consequence of the hydrolysis reaction, that remain in the Pc material. Thus, ca. 50-85% of the protons released by the hydrolysis either protonate the macrocycles or react with Pc + O 2 -already present in the film. In both cases, anions are necessary to neutralize the excess of positive charges. H 2 O is also found in the modified films. The presence of protonated Pcs, of anions, and of H 2 O into what is now HOAlPc (after ClAlPc hydrolysis) modifies the structure of the material as well as its photoactivity.

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Section: Resultsmentioning

confidence: 99%

Highly Photoactive Molecular Semiconductors: Determination of the Essential Parameters That Lead to an Improved Photoactivity for Modified Chloroaluminum Phthalocyanine Thin Films

et al. 1996

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“…Dominant and unavoidable impurities under “clean” conditions are water and molecular oxygen. It is well known that oxygen favors formation of Pc + according to Pc + O 2 → Pc + + O 2 - . − This reaction also reduces the Pc - concentration of the autoionization equilibrium and leads, in many examples, to p-type conductance. From transient oxygen-induced dark conductivity, a CT complex PcO 2 has been postulated as precursor for charge separation by oxygen .…”

Section: Dark Conductivitymentioning

confidence: 99%

Study of Substituent Effects on the Photoconductivity of Soluble 2,(3)- and 1,(4)-Substituted Phthalocyaninato- and Naphthalocyaninatotitanium(IV) Oxides

et al. 1998

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Soluble alkyl (II, 8a,b), fluoroalkyl (4a), and fluoroalkoxy (4b,c, 8c) 1,(4)- or 2,(3)-substituted phthalocyaninato- and linear 2,(3)- and angular 1,(2)-annulated naphthalocyaninatotitanium(IV) oxides 10, 12, and 14 were synthesized and characterized with regard to their spectroscopic, photophysical, and photochemical properties. While alkyl- and fluoroalkoxy-substituted compounds are highly soluble in nonpolar solvents, e.g., hexane, fluoroalkyl-substituted compounds are better soluble in polar aprotic solvents such as acetone. The stability against photooxidation in solution is enhanced on going from alkylated phthalocyanines 1,(4)-(C5H11)8PcTiO (8a), 1,(4)-(C6H13)8PcTiO (8b), and 2,(3)-(C4H9)8PcTiO (II) to fluorinated phthalocyanines 2,(3)-(CF3)4PcTiO (4a), 2,(3)-(CF3CH2O)4PcTiO (4b), and 2,(3)-(CF3CH2O)8PcTiO (4c), from phthalocyanines to naphthalocyanines (tert-butyl)4-2,(3)-NcTiO (10), 1,(2)-NcTiO (12), and (tert-butyl)4-1,(2)-NcTiO (14), and on going from 2,(3)-substituted 4a−c to 1,(4)-substituted phthalocyanines 8a−c. Thin films of these compounds, prepared by either vacuum deposition or spin casting, are classified into three types according to increasing intermolecular π−π interactions. Type α films, characterized by absence of exciton splitting, are formed from 1,(4)-substituted phthalocyanines 8a−c. These films show low dark conductivities and photoconductivities and are considerably sensitive to photooxidation. Type β films, characterized by weak exciton splitting, are formed from fluorinated phthalocyanines 4a−c as well as from rapidly deposited 2,(3)-substituted phthalocyanines II and the unsubstituted PcTiO (I). These films show enhanced photoconductivity and are generally more stable against photooxidation than type α films. Type γ films, formed by slow deposition of II, 10 and unsubstituted phthalocyanine I, are classified by a largely red-shifted B-band absorbing in the near-IR. These films are highly photosensitive as well as stabilized against photooxidation. Steady-state photoconductivities and dark conductivities in thin films are strongly dependent on oxygen partial pressure. Alkylated PcTiO's such as 8a, 8b, and II are found to be p-type conductors (positive oxygen influence on conductivities) like unsubstituted PcTiO (I), whereas angularly annulated naphthalocyanines such as 12 and 14 as well as fluorinated PcTiO's 4a−c are n-type conductors (negative oxygen influence on conductivity). These findings are rationalized by comparison with experimental and theoretical literature data.

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“…It is well known that the photo-induced charge transfer properties of materials have important influences on their photocatalytic activity. The surface photovoltage (SPS) method is a well-established nondestructive technique for the characterization of semiconductors, which has been successfully employed in the study of charge transfer properties in photo-induced surface interactions, 22 dye-sensitized processes, 23 as well as photocatalysis. 24 This method has been shown in studying the photo-induced charge transfer properties of ZnO nanocrystals, 25 Fe 2 O 3 nanorods array, 26 and TiO 2 powder.…”

Section: Introductionmentioning

confidence: 99%

Self-assembled 3D hierarchical clew-like Bi2WO6 microspheres: Synthesis, photo-induced charges transfer properties, and photocatalytic activities

Wang

et al. 2011

CrystEngComm

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Increasing the quantum efficiency of nickel phthalocyanine films by oxygen adsorption

Cited by 31 publications

References 11 publications

Highly Photoactive Molecular Semiconductors: Determination of the Essential Parameters That Lead to an Improved Photoactivity for Modified Chloroaluminum Phthalocyanine Thin Films

Highly Photoactive Molecular Semiconductors: Determination of the Essential Parameters That Lead to an Improved Photoactivity for Modified Chloroaluminum Phthalocyanine Thin Films

Study of Substituent Effects on the Photoconductivity of Soluble 2,(3)- and 1,(4)-Substituted Phthalocyaninato- and Naphthalocyaninatotitanium(IV) Oxides

Self-assembled 3D hierarchical clew-like Bi2WO6 microspheres: Synthesis, photo-induced charges transfer properties, and photocatalytic activities

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