Liquid Crystalline Rylenediimides with Highly Order Smectic Layer Structure as a Floating Gate for Multiband Photoresponding Photonic Transistor Memory

Abstract

With the growing demands of light fidelity technology, photonic transistor memory has gained considerable attention for next‐generation optoelectronic devices. In this work, alkylated rylenediimides of 2,9‐diphenethylanthra[2,1,9‐def:6,5,10‐d“e”f]diisoquinoline‐1,3,8,10(2H,9H)‐tetraone (C8‐PDI) and 2,7‐dioctylbenzo[lmn][3,8]phenanthroline‐1,3,6,8(2H,7H)‐tetraone (C8‐NDI), and pyromellitic diimide of 2,6‐dioctylpyrrolo[3,4‐f]isoindole‐1,3,5,7(2H,6H)‐tetraone (C8‐PMDI) have been used as floating gate electrets in the photonic field‐effect transistor‐type memory. The structure‐optics‐performance relationship of these rod‐like molecules has been systematically studied, and the memory device exhibited a decent response to photowriting and electrical erasing processes, owing to the 3D ordered smectic layer structure and brickwork stacking. Therefore, an evenly distributed photogating moiety, efficient exciton dissociation associated with decent carrier tunneling and charge trapping can be obtained. Among them, the sought‐after C8‐NDI presents favorable energy level alignment, multiband photoresponding, and an optimal block ratio. The fabricated photonic memory with C8‐NDI electret presented a remarkable memory switchability with a memory ratio of 104 and a stable memory ratio of 105 over 10,000 s. To the best of knowledge, this is the first work to utilize rylenediimides based liquid crystals as an efficient charge blocking electret, and these findings open an avenue for designing rod‐like molecules with highly ordered liquid crystalline properties in the ultrafast photomemory devices.

Fast Photoresponsive Phototransistor Memory Using Star-Shaped Conjugated Rod–Coil Molecules as a Floating Gate

“…Phototransistor memory with a direct heterojunction design typically requires a gate bias to program and read the device owing to the lack of a charge-blocking medium. ,− Therefore, organic-molecule-based electrets were tailored using nanostructures to improve their charge storage capability. For example, layer structures with an end-on orientation stabilize the trapped charge in the self-assembled insulated layers. ,,, However, insulated blocking layers with an end-on orientation also form a barrier that hinders carrier tunneling during the photowriting process. Therefore, a face-on orientation is more favorable than an end-on orientation for organic-molecule-based electrets to improve the photoresponse of a memory device.…”

“…Diverse electret designs have been developed to improve the performance of phototransistor memory, including floating gates, − photoactive polymers, − and organic molecules. − Floating-gate electrets consist of photoactive materials (including perovskite nanocrystals, − metal nanoparticles, fluorescent dyes, and quantum dots) dispersed in an insulating polymer matrix. Photoactive polymer electrets are divided into three categories: (i) conjugated/insulated polymer blends; − (ii) conjugated block copolymers; − and (iii) photoluminescent polymers utilizing aggregation-enhanced emission, aggregation-induced emission, or aggregation-caused quenching effect .…”

“…Typically, organic-molecule electrets are tailored with a layered (rod-like molecules) or nanoarray (disc-like molecules) structure or are used in heterojunctions with a semiconducting channel to facilitate charge-trapping functionality. In contrast to floating-gate or polymer electrets, organic-molecule electrets, which exhibit bulk homogeneity and well-defined crystalline structures, are regarded as promising candidates for achieving high-performance memory.…”

“…Furthermore, photoactive polymer electrets easily possess an ambipolar charge-trapping propensity, causing an equivocally defined memory state and destructive readout, which threatens the stability of the memory device. 26,28,31−33 Typically, organic-molecule electrets are tailored with a layered (rod-like molecules) 34 or nanoarray (disc-like molecules) 35 structure or are used in heterojunctions with a semiconducting channel 36 to facilitate charge-trapping functionality. In contrast to floating-gate or polymer electrets, organic-molecule electrets, which exhibit bulk homogeneity and well-defined crystalline structures, are regarded as promising candidates for achieving high-performance memory.…”

Recent Advances in Organic Phototransistors: Nonvolatile Memory, Artificial Synapses, and Photodetectors

“…[ 115 ] In addition to the rod–coil molecules, Lin et al reported the use of rod‐like molecules of alkylated rylenediimides of 2,7‐dioctylbenzo[ lmn ][3,8]phenanthroline‐1,3,6,8(2 H ,7 H )‐tetraone (C8‐NDI) and pyromellitic diimide of 2,6‐dioctylpyrrolo[3,4‐f]isoindole‐1,3,5,7(2 H ,6 H )‐tetraone (C8‐PMDI) as phototransistor memory electrets. [ 116 ] The rylenediimide films were thermally annealed at temperatures above their phase‐transition points to form liquid crystals, and homotropically aligned films were obtained by cooling from the liquid‐crystalline phases. The resulting rylenediimide films with 3D‐ordered smectic layer structures and brickwork stackings constituted effective phototransistor memory electrets, and a memory device obtained by combining them with an n‐type channel of BPE−PDI demonstrated an acceptable memory ratio of 10 5 over 10 4 s.…”