Boosting the Photoresponse of Transistor Memory Utilizing the Ferroelectric Polarization Effect of Polyfluorene/PVDF-Based Copolymer Blends

In this study, a ferroelectric phototransistor memory is developed by blending poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) with a conjugated polymer, poly(9,9-dioctylfluorene) (PFO), at ratios of 4:1, 1:1, and 1:4, using the polymer blending systems as the electrets. The impact of ferroelectric polarization on phototransistor memory is investigated. Since the strong intermolecular interactions introduced by P(VDF-TrFE) and the formation of a typical ferroelectric crystalline phase, the electrical performance of the ferroelectric phototransistor memory with conjugated PFO, which provides strong photoresponse, is significantly improved. Electrical characterization of the memory devices shows that increasing the P(VDF-TrFE) ratio enhances the current stability, with the 1:4 blending ratio achieving a high memory ratio (I ON/I OFF) of up to 106. Additionally, when a gate voltage is applied during the photowriting process, the device exhibits a distinct ferroelectric polarization effect to boost the photoresponse and long-term stability with an I ON/I OFF ratio close to 108 and maintained after 10,000 s. This improvement is also attributed to the channel's prolonged and electret's shortened exciton lifetimes using time-resolved photoluminescence spectroscopy with different light excitations. Both are beneficial for boosting the channel's photocurrent and charge trapping in the electret. This study reveals that a ferroelectric and photoresponsive electret can significantly influence phototransistor memory's optical, morphological, and electrical properties, improving memory behavior and stability. Compared to the traditional bilayer structures comprising ferroelectric dielectric and photoresponsive electret, this design significantly simplifies the ferroelectric photomemory's device architecture. This provides an approach for developing efficient and stable ferroelectric phototransistor memory devices for future applications.