SCIENTIFIC HIGHLIGHTS

Organic electroactive molecules on surfaces for the development of electronic devices

Electroactive molecules assembled on substrates have been employed for the development of: 1) a water actuator that operates at low voltage and 2) a reliable n-type organic field-effect transistor.

The self-assembly of organic electroactive molecules on surfaces can lead to the development of advanced electronic devices with additional advantages compared to their inorganic counterparts such as low-cost, compatibility with flexible substrates or low-voltage operation. In this direction, we highlight here two recent works.

In the first work [1], a single self-assembled monolayer of an anthraquinone derivative is covalently anchored on a conducting indium‐tin oxide (ITO) substrate. By the application of a voltage, the redox state of the molecule can be switched which, in turn, modifies significantly the wetting properties of the substrate. This effect has been exploited for droplets actuation at low voltage. The device was further integrated in a microfluidic system to perform mixing and dispensing on sub‐nanoliter scale. Further, vehiculation of cells across microfluidic compartments was made possible by taking full advantage of surface electrowetting in culture medium.

In the second work [2], crystalline thin films of organic electroactive molecules can be applied as active semiconducting materials in field-effect transistors (OFETs). In particular, solution-processed n-type OFETs are essential elements for developing large-area, low-cost, and all organic logic/complementary circuits. Nonetheless, the development of air-stable n-type organic semiconductors (OSCs) lags behind their p-type counterparts. The trapping of electrons at the semiconductor−dielectric interface leads to a lower performance and operational stability. In this second work, we report printed small-molecule n-type OFETs based on a blend of an electron acceptor molecule with a binder insulating polymer. The latter enhances the device stability due to the improvement of the semiconductor−dielectric interface quality and a self-encapsulation of the OSC. Both combined effects prevent the fast deterioration of the device.

Authors:
Maria Serena Maglione,1 Antonio Campos,1 Sergi Galindo-Riera,1 Joaquim Puigdollers,2 Stefano Casalini,1 Stamatis Georgakopoulos,1 Marianna Barbalinardo,3 Vitaliy Parkula,3 Núria Crivillers,1 Concepció Rovira,1 Pierpaolo Greco,3 Marta Mas-Torrent 1

Affiliations:
1Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Spain
2Department Enginyeria Electrònica, Universitat Politècnica de Catalunya, Spain
3Scriba Nanotecnologie, Italy

Publications:
[1] Fluid Mixing for Low-Power 'Digital Microfluidics' Using Electroactive Molecular Monolayers
Small, 1703344 (2018)
DOI: 10.1002/smll.201703344
[2] Reduction of Charge Traps and Stability Enhancement in Solution-Processed Organic Field-Effect Transistors Based on a Blended n-Type Semiconductor
ACS Appl. Mater. Interfaces 10, 18, 15952 (2018) 
DOI: 10.1021/acsami.8b02851

Figure Caption:
A) Microfluidic system embedded on an ITO surface functionalized with a self-assembled monolayer of an anthraquinone derivative. Upon de application of a voltage the molecules are reduced and the water actuation is controlled.
B) Deposition of the organic semiconductor PDI8CN2 by bar-assisted meniscus shearing. The blending of the material with polystyrene (PS) enhances the device response.

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