Synergistic Effects of Self-Doped Nanostructures as Charge Trapping Elements in Organic Field Effect Transistor Memory

Despite remarkable advances in the development of organic field-effect transistor (OFET) memories,over recent years, the charge trapping elements remain confined to the critical electrets of polymers, nanoparticles, or ferroelectrics. Nevertheless, rare reports are available on the complementary advantages of different types of trapping elements integrated in one single OFET memory. To address this issue, we fabricated two kinds of pentacene-based OFET memories with solution-processed amorphous and beta-phase poly(9,9-dioctylfluorene) (PFO) films as charge trapping layers, respectively. Compared to the amorphous film, the beta-PFO film has self-doped nanostructures (20-120 nm) and could act as natural charge trapping elements, demonstrating the synergistic effects of combining both merits of polymer and nanoparticles into one electret. Consequently, the OFET memory with beta-PFO showed nearly 26% increment in the storage capacity and a pronounced memory window of similar to 45 V in 20 ms programming time. Besides, the retention time of beta-PFO device extended 2 times to maintain an ON/OFF current ratio of 103, indicating high bias-stress reliability. Furthermore, the beta-PFO device demonstrated good photosensitivity in the 430-700 nm range, which was attributed to the additive effect of smaller bandgap and self-doped nanostructures of beta-phase. In this regard, the tuning of molecular conformation and aggregation in a polymer electret is an effective strategy to obtain a high performance OFET memory.