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.
Organic phototransistors have been vigorously investigated for their superior charge-transport performance, photosensitivity, and compatibility with integrated circuits. Accordingly, liquid crystal molecules have been proven to be a high-performance organic electret, and discotic liquid crystal with a face-on orientation is able to show ultrafast photoresponse. Thus far, there is still no application of discotic liquid crystal as a charge-trapping electret in phototransistors. In this study, a series of discotic liquid crystalline molecules consisting of alkyl-triphenylene (Cx-TP, where x = 1, 6, 8, and 10) were designed and applied as an electret in the ultraviolet light-sensitive photomemory. The discotic liquid crystal with optimized side-chain length produced a homeotropically aligned nanoarray structure and endowed the best performance and photoresponse in phototransistor memory. Therefore, C6-TP- and C8-TP-based devices produced high memory ratios of approximately 103 and 104, respectively, which outperformed their analogues of C1-TP and C10-TP with a memory ratio of approximately 102. This achievement indicates the columnar hexagonal structure induced by the homeotropic alignment during liquid crystalline transition produces a huge impact on the photoresponse and device performance. The result of this study underlines the potential of discotic liquid crystals as a photoactive electret in phototransistor applications.
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