Photo-switchable
organic field-effect transistors (OFETs) represent
an important platform for designing memory devices for a diverse array
of products including security (brand-protection, copy-protection,
keyless entry, etc.), credit cards, tickets, and multiple wearable
organic electronics applications. Herein, we present a new concept
by introducing self-assembled monolayers of donor–acceptor
porphyrin–fullerene dyads as light-responsive triggers modulating
the electrical characteristics of OFETs and thus pave the way to the
development of advanced nonvolatile optical memory. The devices demonstrated
wide memory windows, high programming speeds, and long retention times.
Furthermore, we show a remarkable effect of the orientation of the
fullerene–polymer dyads at the dielectric/semiconductor interface
on the device behavior. In particular, the dyads anchored to the dielectric
by the porphyrin part induced a reversible photoelectrical switching
of OFETs, which is characteristic of flash memory elements. On the
contrary, the devices utilizing the dyad anchored by the fullerene
moiety demonstrated irreversible switching, thus operating as read-only
memory (ROM). A mechanism explaining this behavior is proposed using
theoretical DFT calculations. The results suggest the possibility
of revisiting hundreds of known donor–acceptor dyads designed
previously for artificial photosynthesis or other purposes as versatile
optical triggers in advanced OFET-based multibit memory devices for
emerging electronic applications.
Light control over currents in molecular junctions is desirable as a non-contact input with high spectral and spatial resolution provided by the photonic input and the molecular electronics element, respectively. Expanding the study of molecular junctions to non-metallic transparent substrates, such as indium tin oxide (ITO), is vital for the observation of molecular optoelectronic effects. Non-metallic electrodes are expected to decrease the probability of quenching of molecular photo-excited states, light-induced plasmonic effects, or significant electrode expansion under visible light. We have developed micron-sized, metal free, optically addressable ITO molecular junctions with a conductive polymer serving as the counter-electrode. The electrical transport was shown to be dominated by the nature of the self-assembled monolayer (SAM). The use of amino-silane (APTMS) as the chemical binding scheme to ITO was found to be significant in determining the transport properties of the junctions. APTMS allows high junction yields and the formation of dense molecular layers preventing electrical short. However, polar amino-silane binding to the ITO significantly decreased the conductance compared to thiol-bound SAMs, and caused tilted geometry and disorder in the molecular layer. As the effect of the molecular structure on transport properties is clearly observed in our junctions, such metal-free junctions are suitable for characterizing the optoelectronic properties of molecular junctions.
Controlling
charge transfer at indium-doped tin oxide (ITO)/conductive
polymer junctions is of special importance for organic photovoltaic
(OPV) devices and organic light emitting diodes (OLEDs), where ITO
is often the transparent electrode of choice. Light induced conductance
enhancement, i.e., photoconductance, can allow such control. ITO/conductive
polymer junctions are shown herein to exhibit photoconductance under
UV illumination mostly due to photoinduced decrease of an electron
barrier at the ITO–polymer interface by discharging of ITO
extrinsic surface states, related to the adsorption of oxygen species.
Furthermore, we show that ITO surface modification by photoactive
porphyrin adsorption can sensitize the ITO/conductive polymer junctions,
extending the photoconductance to the visible range, to which ITO
is transparent. This process is ascribed mostly to discharging of
ITO adsorbate states by recombination with photogenerated holes in
the photoexcited molecules. Such sensitization is highly relevant
for organic optoelectronic devices utilizing ITO interfaced with photoactive
organic species and operating in the visible range, such as OPV and
OLED devices, and might be applicable also to other UV-photoconductive
metal oxide electrodes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.