High-performance stretchable resistive memories using donor-acceptor block copolymers with fluorene rods and pendent isoindigo coils

Diblock copolymers consisting of electron-donating poly[2,7-(9,9-dihexylfluorene)] (PF) rods and electron-withdrawing poly (pendent isoindigo) (Piso) coils were designed and synthesized through a click reaction. The electronic properties and interchain organization of the copolymers could be tuned by varying the PF/Piso ratio (PF14-b-Piso(n) (n= 10, 20, 60 and 100)). The highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels of the studied polymers were progressively reduced as the length of Piso increased, affecting the charge trapping and intramolecular charge transfer environment between PF and Piso domains. Thermally treated PF14-b-Piso(n) thin films exhibited a clear nanofibrillar structure, and the d-spacing was enhanced systematically as the Piso chain length increased. Resistive memory characteristics were explored with a sandwich indium tin oxide/PF14-b-Piso(n)s/Al device configuration. The enhanced conjugated PF conducting channels led to stable resistance switching behavior, exhibiting volatile SRAM (static random access memory) (PF14-b-Piso(10)) and nonvolatile WORM (write-once-read-many-times) (PF14-b-Piso(20), PF14-b-Piso(60), PF14-b-Piso(100)) characteristics with a large ON/OFF ratio (10(6)) and a stable retention time (10(4) s). A more appealing feature is that such memory cells were integrated on a soft poly(dimethylsiloxane) substrate, allowing for the development of a stretchable data storage device. Reliable and reproducible electrical characteristics, including SRAM- and WORM-type memories, could be explored as the device was stretched under an applied tensile strain ranging from 0 to 50%. The studied donor-acceptor copolymers indeed showed great potential for stretchable electronic applications with controllable digital information storage characteristics.