Reversible switching through irradiation of capacitors and organic transistors employing dielectrics blended with non-ionic molecular photoswitches

Abstract

One promising approach to introduce additional functionalities for sensing and memory applications into conventional organic electronic devices is the introduction of stimuli responsive additives, such as molecular switches. These small organic molecules undergo reversible isomerization between (at least) two isomers when irradiated with light of different wavelength resulting in drastic changes in physicochemical properties such as frontier orbital energy levels, dipole moment and/or molecular geometry. These reversible changes in molecular properties can be exploited to deliberately modify charge transport in organic field-effect transistors and therefore enable optical control over device characteristics. Here, stimuli-responsiveness of organic transistors is achieved by incorporating the dihydroazulene/vinylheptafulvene (DHA/VHF) molecular switches into the gate dielectric. To systematically explore this novel approach, we firstly provide a detailed evaluation of the dielectric properties of the DHA/VHF blends with the dielectric polymer poly(methyl methacrylate) in metal-insulator-metal capacitors using impedance spectroscopy. Afterwards, these switchable dielectric blends are employed as gate dielectrics in OFETs, allowing optical control over device characteristics and figures of merit such as field-effect mobility and threshold voltage. Furthermore, optical absorption spectroscopy shows that DHA/VHF molecular switches (unlike the well-known spiropyran/merocyanine photoswitch) exhibit excellent resistance to cycling fatigue when incorporated into insulating PMMA matrices.