Development of Multilevel Organic Phototransistor Memory using Conjugated/Insulating Polymer Blends with a Vertical Phase Separation

In this work, a series of methacrylate-based polymers bearing benzene (poly(benzyl methacrylate)), naphthalene (poly(2-naphthyl methacrylate)), anthracene (poly(9-anthracenyl methyl methacrylate), PAMA), and pyrene (poly(1-pyrenemethyl methacrylate)) are blended with conjugated polymer of poly(3-hexylthiophene) (P3HT) to perform vertical phase separation during spin-coating. The bilayer structure of the conjugated/insulating polymer blend is driven by their mismatch in surface energy, and the blend films are applied in the phototransistor memory device with the bottom layer of methacrylate-based polymer as a photoactive electret and the top layer of P3HT as a semiconducting channel. It is found that the vertical phase separation morphology, conjugation, and energy levels of the pendant arene groups in the methacrylate-based polymers are highly related to the photoresponse, memory retention/endurance of the phototransistor memory. Therefore, the device comprising the polymer blend of P3HT and PAMA successfully produces a high current contrast of 10⁵ to 254 nm light and 10⁴ to 450 nm light over 10⁴ s. This study provides a facile approach to the fabrication of high-performance phototransistor memory devices.