Stretchable OFET Memories: Tuning the Morphology and the Charge-Trapping Ability of Conjugated Block Copolymers through Soft Segment Branching

Abstract

The mechanical properties and structural design flexibility of charge-trapping polymer electrets has led to their widespread use in organic field-effect transistor (OFET) memories. For example, in the electrets of polyfluorene-based conjugated/insulating block copolymers (BCPs), the confined fiber-like polyfluorene nanostructures in the insulating polymer matrix act as effective hole-trapping sites, leading to controllable memory performance through the design of BCP. However, few studies have reported intrinsically stretchable charge-trapping materials and their memory device applications, and a practical method to correlate thin film morphology of BCP electrets with their charge-trapping ability has not yet been developed. In this study, a series of new conjugated/insulating BCPs, poly(9,9-di-n-hexyl-2,7-fluorene)-block-poly(δdecanolactone)s (PF-b-PDLx, x = 1-3) as stretchable hole-trapping materials are reported. The linear and branched PDL blocks with the comparable molecular weight were used to investigate the effect of polymer architecture on morphology and device performance. Moreover, coverage area of the polyfluorene nanofibers on the BCP films was extracted from atomic force microscopy images, which can be correlated with the trapping density of the polymer electrets. The branched PDL segments not only improve stretchability but also tailor crystallinity and phase separation of the BCPs, thus increasing their charge-trapping ability. The OFET memory device with PF-b-PDL3 as electret layer exhibited the largest memory window (102 V), and could retain its performance at up to 100% strain. This research highlights the importance of BCP design for developing stretchable charge-trapping materials.

Combining Electrospinning and Electrode Printing for the Fabrication of Stretchable Organic Electrochemical Transistors

“…Interest in plastic electronics has been fuelled by the development of new synthetic methods for preparing conjugated organic materials, that enable organic electronics such as OLEDs, OPVDs, and OFETs [1][2][3]. Research in this field has further been motivated to bring the intrinsic properties of plastic electronics to fruition.…”

“…Given intrinsically conductive electrodes underpin the electrochemical performance of devices, the conductivity of these conjugated organic materials must not be compromised under the typically mechanical stresses and strains that are encountered when wear electronics. Indeed, this remains the principal challenge of the field, despite the many fabrication [11] and performances [12,13] improvements of stretchable devices.…”

Fabrication of Nanodevices Through Block Copolymer Self-Assembly

“…Similarly, memory nanodevices have also been successfully obtained by using poly(n-butyl acrylate)-block-maltoheptaose (PBA-b-MH) with linear AB-type, ABA-type, and star-shaped architectures (Hung et al, 2018); polystyrene-blockmaltoheptaose (PS-b-MH) with different morphologies and orientations (Chuang et al, 2020); or poly(9,9-di-n-hexyl-2,7fluorene)-block-poly(δ-decanolactone) (PF-b-PDL) with AB, AB 2 , and AB 3 architectures (Hsu et al, 2021). Moreover, an ultrafast photo-responsive nonvolatile flash memory was prepared by combining a BCP template with perovskite (Chang et al, 2020).…”

Recent Progress in Conducting Polymer Composite/Nanofiber-Based Strain and Pressure Sensors

“…The upcoming surge in elevating the eco-friendliness and bio-compatibility remains as another crucial task for the researchers to benefit the human society. Material choice ranging from rigid, flexible, and stretchable polymers, along with conductive nanostructures, including nanoparticles, nanowires, nanorods, nanoflakes, nanosheets, and nanofibers, pave the way to upgrades in the sensors' real-time suitability [9][10][11].…”