Periodic Reporting for period 1 - 2D-EG-FET (Printed Optoelectronic Devices from Nanosheet Network Electrochemically-gated Field Effect Transistors)
Reporting period: 2016-05-16 to 2018-05-15
This project was focused on fabricating printed ensembles of semiconducting nanosheets (i.e. semiconducting nanosheet networks, SNNs) with controlled composition, and characterising their properties as the active material within solution-processable electrochemically-gated field-effect transistors (E-gated FETs).
Numerous layered semiconductors, such as members of transition metal dichalcogenides (e.g. WS2 and MoS2) are naturally abundant and can be made accessible in large quantities in a printable form by liquid phase exfoliation (LPE), which converts the parent crystal into liquid dispersed nanosheets. However, presently little is known about the influence of particular dispersion media, geometry of the flake constituents (i.e. mean flake length and number of layers), the chosen deposition approach, and post processing on the resulting SNN properties.
In particular, it is unknown how to produce sufficient quantities of monolayer enriched inks and a means of depositing them in a manner that prevents flake restacking, such that printed networks with direct bandgap characteristics can be retained. Such networks could then be investigated for optoelectronic applications, such as light-emitting FETs.
Importance for society:
By combining versatile and scalable solution-processing methods with the excellent solid state properties of layered crystalline nanomaterials, it is hoped that this work will lead to a wide range of applications in printed electronics. It is envisaged that this approach will give rise to applications that are impossible using traditional manufacturing approaches (i.e. based on silicon), such as devices that are mechanically deformable (i.e. flexible and stretchable) when deposited on plastic foil substrates, and easily customised for diverse purposes. Such high performance printed electronics, when realised, will enable the integration of electronic functionality in new locations and situations where numerous applications will be found, such as inexpensive hardware for the Internet of Things.
The overall research objectives were: (1) to prepare size selected inks by liquid phase exfoliation, (2) process these into nanosheet networks with controlled morphology and composition using industrially relevant solution deposition methods, (3) fabricate electrolyte-gated field effect transistors based on these nanosheet networks and (4) characterise their electronic transport properties under electrochemical control, especially those produced to retain monolayer properties with the intent to demonstrate electroluminescence from these printed SNNs for the first time. Following this, we wish to (5) realise all-printed E-gated FETs by printing all of the device components, i.e. the SNN channel material, as well as nanomaterial based metal contact and gate electrodes.
The obtained results were primarily exploited through presentations (talks and posters) at a number international conferences, including a Hengstberger Symposium at the Internationales Wissenschaftsforum Heidelberg.
The demonstration of ambipolar transport behaviour (simultaneous injection of electrons and holes) is a requirement for subsequent demonstration of light-emitting FETs based on printed semiconducting nanosheet networks. Hence, the completed work marks important progress towards the realisation of high performance printed electronics based on layered nanomaterials.