Revealing the memory effect in phototransistors with vertical phase separation of conjugated/insulating polymer blends through film-on-water interface self-assembly

This study utilizes a blend of poly (3-hexylthiophene) (P3HT) and poly (1-pyrenemethyl methacrylate) (PPyMA) polymers to achieve vertical phase separation through air/liquid interface self-assembly. Due to the surface energy mismatch of these blends, a bilayer structure is formed between the conjugated and insulating polymers. The blended thin films are applied to phototransistor memory devices, with PPyMA as a photoactive electret and P3HT as a semiconductor channel. A comparative study of the two-transfer direction water side (forward structure) and air side (reverse structure) reveals that the vertical phase separation morphology of the aromatic side groups in PPyMA, along with its conjugation, is closely related to the photoresponse, memory retention, and durability of the photomemory devices. Electrical analysis shows that the device fabricated with the forward transfer (P3HT/PPyMA) can achieve photo writing through exposure to ultraviolet light at 265 nm, 310 nm, 365 nm, and blue light at 455 nm, while electrical erasure is performed via gate bias, resulting in a wide memory window (∼48.7 V). The device also exhibits a stable memory ratio in repeated write/erase measurements and long-term stability exceeding 10⁴ s. In contrast, the device fabricated with the reverse transfer (PPyMA/P3HT), due to the reverse bilayer structure, required hole injection to pass through the insulating PPyMA layer, and holes may recombine with stored electrons during vertical transport, thereby dismissing the memory mechanism. As a result, the device cannot effectively store charges to achieve memory retention. This study demonstrates vertical phase separation through air/liquid interface self-assembly and reveals the photoresponse and charge storage mechanisms of photomemory devices.