Bulk charge transport in liquid-crystalline polymer semiconductors based on poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene)

Abstract

The class of liquid-crystalline semiconducting polymers based on poly(2,5-bis(3-alkylthiophen-2yl)thieno[3,2-b]thiophene) recently has attracted significant interest in the field of organic electronics, predominantly due to their promising performance in field-effect transistor (FET) structures with device mobilities reaching-if not exceeding-those of amorphous silicon architectures. Less is known, however, about the bulk charge-transport properties of these interesting macromolecules. We therefore conducted time-of-flight (TOF) photoconductivity measurements on one particular material of this class of organic semiconductors-i.e. poly(2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene), pBTTT-C 12 -and attempted to correlate the electronic bulk properties of this polymer with its microstructural development with temperature. The effect of annealing was also investigated.

Solid‐State Processing of Organic Semiconductors

“…Similar observations were made with PBTTT-C 16 (solid-state pressed at 100 ° C; see the Supporting Information, Figure S4), for which bulk charge-carrier mobilities increased by about one order of magnitude with respect to solution-cast structures ( μ TOF solid-state = 1 · 10 − 4 -5 · 10 − 4 cm 2 V − 1 s − 1 , compared to room temperature μ TOF solution-cast = 5 · 10 − 6 -5 · 10 − 5 cm 2 V − 1 s − 1 ). [ 27 ] Interestingly, μ TOF was found to be essentially fi eld-independent for solid-state processed PBTTT-C 16 , indicating reduced energetic disorder when compared to solution-cast structures, which usually displayed a distinct fi eld dependence.…”

Confined Crystallization within Cylindrical P3EHT Block Copolymer Microdomains

“…Conjugated polymers have been applied to light-emitting diodes, solar cells, and transistors which rely crucially on charge mobility. − In these materials, charge mobility is highly influenced by structural details of the resulting crystallinityparticularly crystalline orientationas influenced by factors including confinement, − processing conditions, − mechanism of crystallization, − and details of molecular design and architecture. ,, The study of confinement within controlled geometries and tethering of chain ends presents a unique opportunity to template and control conjugated polymer crystallization. In particular, microphase-separated diblock copolymers present a model system in which confinement geometry and curvature may be controlled to understand their impacts upon the resulting polymer crystallization.…”

On the phase behaviour of organic semiconductors

“…Hence, it is not surprising that the class of liquid‐crystalline semiconducting polymers such as certain polyfluorenes21 and poly{2,5‐bis(3‐alkylthiophen‐2‐yl)thieno[3,2‐b]thiophene}s (PBTTTs)22–24 have recently attracted significant interest in the field of organic electronics. Drastically different charge transport properties have been found for the various mesophases of for example the C 12 ‐substituted poly{2,5‐bis(3‐dodecylthiophen‐2‐yl)thieno[3,2‐b]thiophene} (PBTTT‐C 12 ): the charge‐carrier mobility as measured in time‐of‐flight photoconductivity experiments (µ TOF ) changes from 5 × 10 5 cm 2 V −1 s −1 (at room temperature) to 3 × 10 4 cm 2 V −1 s −1 in its mesophase ( T > 150 °C) 25…”

“…Liquid crystallinity can also be exploited to manipulate the solid‐state microstructure through suitable heat treatment procedures. This can be illustrated by the fact that annealing PBTTT‐C 12 in its mesophase results in considerably higher molecular order and, in parallel, higher charge‐carrier mobility as measured both in time‐of‐flight photoconductivity experiments as well as in transistor devices 25–27. Clearly, the duration of the temperature treatment needs thereby to be optimised to realise maximum electronic performance without degrading the material.…”