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Synthesis of Cyclopentadithiophene-Diketopyrrolopyrrole Donor-Acceptor Copolymers for High-Performance Nonvolatile Floating-Gate Memory Transistors with Long Retention Time.

Organic flash memories that employ solution-processed polymer semiconductors preferentially require internal stability of their active channel layers. In this paper, a series of new donor-acceptor copolymers based on cyclopentadithiophene (CDT) and diketopyrrolopyrrole (DPP) are synthesized to obtain high performance and operational stability of nonvolatile floating-gate memory transistors with various additional donor units including thiophene, thiophene-vinylene-thiophene (CDT-DPP-TVT), selenophene, and selenophene-vinylene-selenophene. Detailed analyses on the photophysical, two-dimensional grazing incident X-ray diffraction, and bias-stress stability are discussed, which reveal that the CDT-DPP-TVT exhibits excellent bias-stress stability over 105 s. To utilize the robust nature of CDT-DPP-TVT, floating-gate transistors are fabricated by embedding Au nanoparticles between CytopTM layers as a charge storage site. The resulting memory devices reveal bi-stable current states with high on/off current ratio larger than 104 and each state can be distinguished for more than 1 year, indicating a long retention time. Moreover, a repetitive writing-reading-erasing-reading test clearly supports the reproducible memory operation with reversible and reliable electrical responses. All these results suggest that the internal stability of CDT-DPP-TVT makes this copolymer a promising material for application in reliable organic flash memory.