Oligosaccharide Block Copolymers with Branched Architectures and Channel Energy Level Optimizations for High-Performance Floating Gate Phototransistor Memory

The nonvolatile phototransistor memory features a fast transmission speed, low latency, and nondestructive orthogonal operation for multibit data storage. Utilizing perovskite quantum dots (QDs) with polymers has been regarded as a facile and efficient approach to fabricating phototransistor memory devices due to their high light responsivity and nonvolatility. In addition, introducing block copolymers improves the QD dispersion and ambient stability. However, the reported study has not investigated the branching architectures of block copolymers (BCPs) influencing memory behavior and the tunability between the channel and the floating gate memory layer. Herein, this study utilizes different numbers of branching arms of carbohydrate-based BCPs, comprising poly(dimethylsiloxane) (PDMS, as A block) and maltotriose (MT, as B block), to promote electrical performance for phototransistor memory. Different rylenediimide-based N-type semiconductors are combined with BCP/QD floating gate dielectrics according to their energy levels. Due to the most substantial QD accommodation conferred by BCPs, the triarms BCP with QD (AB3QD) exhibited the smoothest surface among all BCP/QD nanocomposites, with the best electrical performance for phototransistor memory. Furthermore, the naphthalene diimide (NDI)-based device exhibits the most suitable energy levels for adapting the floating gate layer, resulting in good charge transfer efficiency, photoresponse, and memory stability. The reason can be attributed to the comparable lowest unoccupied molecular orbital (LUMO) energy level for transferring negative charges and the low-lying highest occupied molecular orbital (HOMO) energy level for blocking positive charges, compared to the energy levels of the QD. As an aspect of the device performance, the phototransistor memory renders a high memory ratio of ION/OFF = 3.09 × 105, which outperforms those of rylenediimides such as perylene diimide (PDI, ION/OFF = 4.48 × 104) and pyromellitic diimide (PMDI, negligible ION/OFF), as well as the diarms (ION/OFF = 1.33 × 105) or linear (ION/OFF = 5.06 × 104) BCP counterparts. Additionally, the device exhibits good stability (ION/OFF > 106 over 10,000 s) and decent switchability (ION/OFF > 105 over 10 cycles). In conclusion, the results indicate that the different branching BCP architectures and energy level alignments between the channel and floating gate layers play a vital role in phototransistor memory.