Modeling, synthesis, and testing of materials and devices for organic semiconductor solar cells

Panayotatos, P.; Whitlock, Jonathan B.; Bird, George R.

doi:10.1117/12.130579

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“…Our experiments indeed confirm that the ground ClAlPc powder rapidly (within a few hours) reaches a partially transformed condition, and the transformation then continues very slowly during several days. This behavior has already been reported for heterogeneous reactions involving ClAlPc. , However, it is possible to reach a better completion of the transformation reactions if ClAlPc is replaced by BrAlPc, since aluminum bromide is more reactive than aluminum chloride. Information obtained from the transformation of BrAlPc is very valuable because it has already been shown that both ClAlPc and BrAlPc display similar photoactivities. , …”

Section: Resultssupporting

confidence: 71%

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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