Advanced Nonvolatile Organic Optical Memory Using Self-Assembled Monolayers of Porphyrin-Fullerene Dyads

Abstract

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.

Keywords: OFETs; optical memory; organic field-effect transistors; photoswitching; porphyrin−fullerene dyad; self-assembled monolayer.

Figure 1

Molecular structures of the investigated porphyrin–fullerene dyads with anchoring carboxylic groups attached to the fullerene (PF) or the porphyrin (FP) units thus enabling their different alignment on the dielectric oxide layer (left). Schematic layout of the device architectures incorporating photosensitive monolayers of PF or FP (right).

Figure 2

Evolution of the transfer characteristics of the devices comprising FP (a, b) or PF (c, d) dyads under exposure to positive (writing: V_P = 10 V; a, c) or negative (erasing: V_P = −10 V; b,d) applied bias and violet light (λ = 405 nm) as a function of the programming time.

Figure 3

Evolution of the transfer characteristics of the OFETs comprising FP (a) or PF (c) induced by applying gradually increasing V_P (from 0 to 10 V) and violet light (λ = 405 nm) for 10 ms. Evolution of the OFET threshold voltage as a function of the programming voltage V_P for OFETs assembled using monolayers of FP (b) and PF (d) dyads. The backward programming was done by applying gradually decreasing V_P (from +10 to −10 V) under simultaneous exposure to violet light (λ = 405 nm) for 1 s at each step.

Figure 4

Transfer characteristics illustrating multiple switching of the FP-based OFETs between two distinct electrical states (a) and the irreversible single switching of the devices assembled using the PF dyad (c). OFET drain currents for two distinct electrical states (high-current and low-current) plotted as a function of time illustrate retention characteristics of the memory devices comprising FP (b) or PF (d) dyads.

Figure 5

Schematic illustration of the proposed switching mechanisms of the OFETs comprising (a) FP or (b) PF dyads. (c) Energy level diagrams show the facile hole injection from the FP dyad to AlO_x (left) and the blocked hole injection in the case of the PF dyad (right), as deduced from DFT calculations.