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Fully R2R printed TFTs with highly purified semiconducting SWCNTs?

Printed TFT has been a difficult technology to develop given the complex multi-layer nature of TFTs with their high sensitivity to interfacial and film quality properties. Here (from March 2021), Patrick R. L. Malenfant et al showcases R2R printed TFT sheets with good mobility and low VT variability even over a 10meter print run!


Interestingly, SWCNTs have proven to be a good solution for the semiconductor layer of a printed TFT. SWCNTs are grown as a mixture of metallic (70%) and semiconducting (30%) tubes. Since there is no reliable method yet to only grow semiconducting types, one must separate the two. The best technique is based on use of conjugated polymers, which, through repeated rounds of centrifugation, enables one to disperse and thus separate CNTs based on diameter, chirality and type. This way one can obtain highly pure semiconducting-only SWCNT. Indeed, Raymor Industries Inc. is offering such materials already.


The separated dispersions are not yet printable inks though. To formulate R2R printable inks, Patrick et al recommend a ligand exchange process to replace the hydrophobic polyfluorenes polymers (left over around the tubes as part of the separation process) with a more hydrophilic polymer.


In the video below, Patrick shows that R2R printing of fully TFT is possible with excellent results: the TFTs have mobility range of 0.02-3 cm2/V.s, On/Off ratio of 1E4, and threshold voltage variability of around 6-10% over a 10m R2R print run!


This technology shows the technological viability of R2R printed TFTs based on SC-SWCNT although there is still a long way to mature this technology into a production/commercial solution


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