Switchable Charge Injection Barrier in an Organic Supramolecular Semiconductor

Abstract

We disclose a supramolecular material which combines semiconducting and dipolar functionalities. The material consists of a discotic semiconducting carbonyl-bridged triarylamine core which is surrounded by three dipolar amide groups. In thin films, the material self-organizes in a hexagonal columnar fashion through π-stacking of the molecular core and hydrogen bonding between the amide groups. Alignment by an electrical field in a simple metal/semiconductor/metal geometry induces a polar order in the interface layers near the metal contacts that can be reversibly switched, while the bulk material remains non-polarized.On suitably chosen electrodes, the presence of an interfacial polarization field leads to a modulation of the barrier for charge injection into the semiconductor. Consequently, a reversible switching is possible between a high-resistance, injection-limited off-state and a low-resistance, space-charge-limited on-state. The resulting memory diode shows switchable rectification with on/off ratios of up to two orders of magnitude. This demonstrated multifunctionality of a single material is a promising concept towards possible application in lowcost, large-area, non-volatile organic memories.

Ferroelectric self-assembled molecular materials showing both rectifying and switchable conductivity

“…The hysteresis behavior of the latter is well understood to result from a modulation of the charge injection barrier at the metal-semiconductor interface by the ferroelectric polarization ( 10 , 11 ). The loop sense for these blend devices can be generalized to all devices, where a field-driven redistribution of charge gives rise to a reduction in effective injection barrier height ( 13 , 14 ) and/or an increase in bulk conductivity, and hence to an increase in current ( 28 ). For example, in light-emitting electrochemical cells, the redistribution of ions modulates the injection barrier and enables dynamic doping of the semiconductor component ( 29 ).…”

Triarylamine-Based Supramolecular Polymers: Structures, Dynamics, and Functions

“…Interestingly, TAA derivatives were shown to produce columnar stacks even when bearing very large substituents in solution, [13][14][15][16] in thin films, 14,17 or in the bulk with the formation of various liquid-crystalline mesophases (Figure 1F). 18,19 Strikingly, even when TAA are conjugated to substituents as large as fullerene moieties, 1D or 3D supramolecular polymers can be obtained (Figure 1G). 20,21 Overall, after a few years of investigations, more and more evidence highlights that the propensity of TAA derivatives to stack with one another embodies a quite general rule.…”

“…14,17 In thin films, supramolecular columnar liquid crystals made of TATA can act as a switchable charge injection barrier by combining semiconducting and dipolar functionalities. 19 Besides, TAA nanowires were built within insulating mesoporous silica layers in order to access an hybrid conducting material functioning as a biocathode. 34 In a complementary direction, the group of Sanvito investigated by DFT and Monte Carlo simulations the ability of TAA nanowires to behave as organic semiconductors for spintronic applications.…”

Suppressing depolarization by tail substitution in an organic supramolecular ferroelectric

“…A recently discovered class of amidebased dipolar columnar discotic liquid crystals offers the intriguing opportunity to tune key ferroelectric parameters by side chain modification 15 as well as to introduce semiconducting properties by changing the p-conjugated core. 16,17 Yet, despite having a great potential for various applications, ferroelectric liquid crystals lacked interest from a ferro/piezo/pyroelectric device perspective due to typically high operating temperatures, modest remnant polarization and/or negligible polarization retention. [18][19][20] The archetypical amide-based liquid crystalline ferroelectric is trialkylbenzene-1,3,5-tricarboxamide (BTA), see Fig.…”