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Template and Temperature-Controlled Polymorph Formation in Squaraine Thin Films

[Image: see text] Controlling the polymorph formation in organic semiconductor thin films by the choice of processing parameters is a key factor for targeted device performance. Small molecular semiconductors such as the prototypical anilino squaraine compound with branched butyl chains as terminal...

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Autores principales: Balzer, Frank, Breuer, Tobias, Witte, Gregor, Schiek, Manuela
Formato: Online Artículo Texto
Lenguaje:English
Publicado: American Chemical Society 2022
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9352357/
https://www.ncbi.nlm.nih.gov/pubmed/35858043
http://dx.doi.org/10.1021/acs.langmuir.2c01023
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author Balzer, Frank
Breuer, Tobias
Witte, Gregor
Schiek, Manuela
author_facet Balzer, Frank
Breuer, Tobias
Witte, Gregor
Schiek, Manuela
author_sort Balzer, Frank
collection PubMed
description [Image: see text] Controlling the polymorph formation in organic semiconductor thin films by the choice of processing parameters is a key factor for targeted device performance. Small molecular semiconductors such as the prototypical anilino squaraine compound with branched butyl chains as terminal functionalization (SQIB) allow both solution and vapor phase deposition methods. SQIB has been considered for various photovoltaic applications mainly as amorphous isotropic thin films due to its broad absorption within the visible to deep-red spectral range. The two known crystalline polymorphs adopting a monoclinic and orthorhombic crystal phase show characteristic Frenkel excitonic spectral signatures of overall H-type and J-type aggregates, respectively, with additional pronounced Davydov splitting. This gives a recognizable polarized optical response of crystalline thin films suitable for identification of the polymorphs. Both phases emerge with a strongly preferred out-of-plane and rather random in-plane orientation in spin-casted thin films depending on subsequent thermal annealing. By contrast, upon vapor deposition on dielectric and conductive substrates, such as silicon dioxide, potassium chloride, graphene, and gold, the polymorph expression depends basically on the choice of growth substrate. The same pronounced out-of-plane orientation is adopted in all crystalline cases, but with a surface templated in-plane alignment in case of crystalline substrates. Strikingly, the amorphous isotropic thin films obtained by vapor deposition cannot be crystallized by thermal postannealing, which is a key feature for the spin-casted thin films, here monitored by polarized in situ microscopy. Combining X-ray diffraction, atomic force microscopy, ellipsometry, and polarized spectro-microscopy, we identify the processing-dependent evolution of the crystal phases, correlating morphology and molecular orientations within the textured SQIB films.
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spelling pubmed-93523572022-08-05 Template and Temperature-Controlled Polymorph Formation in Squaraine Thin Films Balzer, Frank Breuer, Tobias Witte, Gregor Schiek, Manuela Langmuir [Image: see text] Controlling the polymorph formation in organic semiconductor thin films by the choice of processing parameters is a key factor for targeted device performance. Small molecular semiconductors such as the prototypical anilino squaraine compound with branched butyl chains as terminal functionalization (SQIB) allow both solution and vapor phase deposition methods. SQIB has been considered for various photovoltaic applications mainly as amorphous isotropic thin films due to its broad absorption within the visible to deep-red spectral range. The two known crystalline polymorphs adopting a monoclinic and orthorhombic crystal phase show characteristic Frenkel excitonic spectral signatures of overall H-type and J-type aggregates, respectively, with additional pronounced Davydov splitting. This gives a recognizable polarized optical response of crystalline thin films suitable for identification of the polymorphs. Both phases emerge with a strongly preferred out-of-plane and rather random in-plane orientation in spin-casted thin films depending on subsequent thermal annealing. By contrast, upon vapor deposition on dielectric and conductive substrates, such as silicon dioxide, potassium chloride, graphene, and gold, the polymorph expression depends basically on the choice of growth substrate. The same pronounced out-of-plane orientation is adopted in all crystalline cases, but with a surface templated in-plane alignment in case of crystalline substrates. Strikingly, the amorphous isotropic thin films obtained by vapor deposition cannot be crystallized by thermal postannealing, which is a key feature for the spin-casted thin films, here monitored by polarized in situ microscopy. Combining X-ray diffraction, atomic force microscopy, ellipsometry, and polarized spectro-microscopy, we identify the processing-dependent evolution of the crystal phases, correlating morphology and molecular orientations within the textured SQIB films. American Chemical Society 2022-07-20 2022-08-02 /pmc/articles/PMC9352357/ /pubmed/35858043 http://dx.doi.org/10.1021/acs.langmuir.2c01023 Text en © 2022 The Authors. Published by American Chemical Society https://creativecommons.org/licenses/by/4.0/Permits the broadest form of re-use including for commercial purposes, provided that author attribution and integrity are maintained (https://creativecommons.org/licenses/by/4.0/).
spellingShingle Balzer, Frank
Breuer, Tobias
Witte, Gregor
Schiek, Manuela
Template and Temperature-Controlled Polymorph Formation in Squaraine Thin Films
title Template and Temperature-Controlled Polymorph Formation in Squaraine Thin Films
title_full Template and Temperature-Controlled Polymorph Formation in Squaraine Thin Films
title_fullStr Template and Temperature-Controlled Polymorph Formation in Squaraine Thin Films
title_full_unstemmed Template and Temperature-Controlled Polymorph Formation in Squaraine Thin Films
title_short Template and Temperature-Controlled Polymorph Formation in Squaraine Thin Films
title_sort template and temperature-controlled polymorph formation in squaraine thin films
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9352357/
https://www.ncbi.nlm.nih.gov/pubmed/35858043
http://dx.doi.org/10.1021/acs.langmuir.2c01023
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