Electret Layer Design for Photowritable n-type Nonvolatile Organic Memory Devices

A photoinduced current enhancement and memory effect were demonstrated in N,N′-ditridecyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C13)-based organic thin-film transistor nonvolatile memory (NVM) devices upon 532 nm laser illumination for 2 min. The devices incorporated a cross-linked poly(4-vinylphenol) (C-PVP) electret layer containing hydroxyphenyl groups, which enabled memory retention exceeding 1 day. The effect originated from two distinct dipoles: a strong instantaneous dipole of 27.9 D generated by photoexcited PTCDI-C13 dimers, and a quasi-permanent dipole aligned within the C-PVP layer. Charge storage behavior was elucidated through electric field–dependent characterization, time-resolved capacitance measurements, and quantum chemical simulations. To verify the role of the hydroxyphenyl group, NVMs were fabricated with different electret materials, including PVP, polystyrene (PS), poly(vinyl alcohol) (PVA), and PS doped with 1 wt % catechol. The photoinduced memory effect was observed exclusively in devices containing hydroxyphenyl or structurally similar functional groups, confirming their essential role in facilitating photoinduced dipole alignment and stable charge retention. These findings provide new insights into the design of photoresponsive organic memory devices with long retention and tunable optoelectronic properties.