Novel fast-switching transistors

The emergence of organic electronics has brought a new era in the field of electronic materials, with organic semiconductors having already been used in flat-panel display devices. Organic molecules can be blended with other molecules to create hybrid materials that retain properties from both parts. This concept allows construction of organic electronic devices that integrate more than one function, which strongly increases the value of the material.

With EU funding, the 'Responsive field-effect transistors: A life-long training career development action' (RESPONSIVE) project explored tailor-made interfaces between semiconductor and photochromic molecules by blending interfaces with metallic electrodes to create light-responsive FETs. Given that photochromic molecules affect the transistor carrier mobility, they play a fundamental role to its light-responsive function by turning on and off charge traps.

RESPONSIVE demonstrated that combining organic semiconductors with photochromic molecules is a promising approach to fabricate photoswitchable transistors that retain the high carrier mobility of the semiconductor.

Photochromic molecules - diarylethenes (DAEs) - were blended as self-assembled monolayers (SAMs) at different interfaces to obtain devices featuring different conductivity when exposed to different light stimuli. Both planar and non-planar interfaces were functionalised with responsive SAMs to affect charge transport in the active semiconducting layer - fullerene derivatives. Given that fullerenes are n-type semiconductors, scientists proved for the first time the photoswitching function in n-type blended FETs.

Using different microscopic and spectroscopic techniques, scientists revealed that the blended films were amorphous, with phase-segregated domains of organic and photochromic molecules. The ability of the latter to photoisomerise in such blended films was found to be critical for the switching efficiency of the photoresponsive devices. Scientists also developed a method to study the switching efficiency of DAEs with differently sized organic molecules.

The developed blended system of organic semiconductor and photochromic molecules has great potential to find application in optical memory elements and high-sensitivity optical sensors.