Thiophene-S,S-dioxidized indophenine for use in organic field effect transistors
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Date
2016-12-23
Authors
Ellard, Jackson
Journal Title
Journal ISSN
Volume Title
Publisher
University of Waterloo
Abstract
To address the need for better n-type organic semiconductors, thiophene-S,S-dioxidized
indophenine (IDTO) was developed. IDTO is a planar quinoidal molecule with deep energy levels
which facilitate stable and efficient electron transport. IDTO is a promising material in the design and
fabrication of high performance n-type organic field-effect transistors because it offers simple
synthesis, as well as excellent processability and good performance. The work presented in this thesis
follows the development of IDTO and its various uses in organic field-effect transistors. Firstly, the
synthetic method for IDTO was systematically improved. Two important factors were improved,
safety was improved by replacing the solvent, benzene, with the much less hazardous toluene and the
yield of the synthesis was increased from less than 10% to ~40%. Next, IDTO and two derivatives (5-
bromo-IDTO and 6-bromo-IDTO) were synthesized and evaluated as new n-type small molecule
organic semiconductors. The three compounds all exhibited unipolar n-type characteristics in the
range of 10-2 to 10-1 cm2V-1s-1. The highest electron mobility of 0.11 cm2V-1s-1 was measured for 6-
bromo-IDTO. IDTO was then utilized as an electron accepting building block for the synthesis of two
donor-acceptor polymers: PIDTOBT and PIDTOBTz. Both polymers showed unipolar n-type
performance with electron mobilities on the order of 10-2 to 10-1 cm2V-1s-1. PIDTOBT had the highest
electron mobility of 0.18 cm2V-1s-1 after annealing at 200 °C. From the small molecule and polymer
results, it is clear that IDTO is a promising material for unipolar n-type organic semiconductors. Since
IDTO has a strong electron accepting feature, it was thought that IDTO would have another use as an
electron trap. By blending IDTO with an ambipolar polymer that has a LUMO energy level above
that of IDTO; electron transport could be suppressed under the correct conditions. The three small
molecule IDTO compounds were blended with PINDFBT (TT) and PINDFBT (HH) to investigate the
electron trapping ability of IDTO. Complete suppression of electron transport was not observed but
the overall trend agreed with the theory. 6-bromo-IDTO having the lowest LUMO energy level
showed the strongest electron trapping effect while IDTO had the weakest effect due to its higher
LUMO energy level. This thesis provides a comprehensive study of the development and application
of the novel material, IDTO.
Description
Keywords
organic field effect transistor