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Directional Crystallization of C8-BTBT-C8 Thin Films in a Temperature Gradient

Abstract

A directional crystallization of compound 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT-C8) based on a temperature gradient approach has been used as a post-deposition process to control the crystalline morphology of thin films. C8-BTBT-C8 films of arbitrary thicknesses have been fabricated by spin-coating and subjected to the directional crystallization process. Dewetting is prevented by the liquid crystal phase of C8-BTBT-C8, allowing the formation of flat and rather uniform thin films with large crystalline domains. Spin-coating concentration, gradient magnitude, and cooling rate have been varied to explore a large set of crystallization conditions and to correlate them with thin film morphology. The latter has been characterized by a combined use of optical profilometer, polarized optical microscopy, X-ray reflectometry, and X-ray diffraction measurements. The characterization results put forward the roughness and crystalline order of thin films are improved after the temperature gradient treatments: 1. high cooling rates treatments (≥ 9 ℃.min-1) significantly reduce the roughness of high thickness films, leading good continuity and uniform of the films; 2. dendritic growth dominates not only the films with low thickness but also films with high thickness treated under low cooling rates (< 9 ℃.min-1); 3. the out-of-plane order and the in-plane alignment of the crystallites are also remarkably enhanced by the temperature gradient treatments.

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Supplementary files

Article information


Submitted
10 Jul 2020
Accepted
05 Oct 2020
First published
05 Oct 2020

Mater. Chem. Front., 2020, Accepted Manuscript
Article type
Research Article

Directional Crystallization of C8-BTBT-C8 Thin Films in a Temperature Gradient

G. Schweicher, G. Liu, P. Fastré, R. Resel, M. Abbas, G. Wantz and Y. Geerts, Mater. Chem. Front., 2020, Accepted Manuscript , DOI: 10.1039/D0QM00472C

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