n-Type Digital Memory Characteristics of Diketopyrrolopyrrole-Based Narrow Bandgap Polymers

New pi-conjugated polymers based on dithienyl-diketopyrrolopyrrole (dtDPP) were synthesized by direct arylation polymerization, that is, poly(dtDPP), poly(dtDPP-FL), and poly(dtDPP-TPA). They revealed extremely low bandgaps, which could be achieved by controlling the donor-acceptor powers among the backbone building blocks. They were all thermally stable up to 250 degrees C and, furthermore, solution-processible in conventional ways, producing good-quality thin films. Poly(dtDPP) favorably self-assembled, forming an edge-on layer structure in nanoscale films, whereas the others were preferentially oriented within the film plane without any regular packing structures. All the dt-DPP-based polymers as active layers in devices demonstrated high-performance n-type digital memories (low switching voltage, high ON/OFF current ratio, and high stability) because of the narrow bandgaps. Moreover, the memory modes (nonvolatile and volatile) could be tuned by adjusting the donor-acceptor powers in the backbone. Overall, the dtDPP-based polymers are suitable for the low-cost mass production of n-type nonvolatile and volatile high performing memory devices. In addition, this study provides a guideline on how to achieve high-performance n-type digital memories by balancing the donor and acceptor powers among the chemical building blocks.