Electrically bistable memory devices based on all-conjugated block copolythiophenes and their PCBM composite films

Abstract

We explore the memory device characteristics of the all-conjugated diblock copolythiophenes, poly(3-hexylthiophene)-block-poly(3-phenoxymethylthiophene) (P3HT-b-P3PT), and their blends with PCBM. The field-effect transistors prepared from P3HT-b-P3PT showed a significant hysteresis between the forward and backward gate-bias scans in the transfer curve, indicating the occurrence of charge trapping. The charge trapping may have occurred within the amorphous P3PT domains dispersed in the block copolythiophene by preventing charge transport. P3HT₅₂5252-bbb-P3PT₃₉3939 and P3HT₁₀₂102-bb-P3PT₃₇37 exhibited dynamic random access memory (DRAM) behavior in the sandwich configuration of ITO/P3HT-b-P3PT/Al, whereas P3HT only showed semiconductor characteristics, suggesting the significant effect of the amorphous P3PT segments on the electrical switching behavior. By blending a small amount (5–10 wt%) of PCBM into P3HT-b-P3PT of different block ratios (P3HT₅₂5252-bbb-P3PT₃₉3939, P3HT₁₀₂102-bb-P3PT₃₇37, and P3HT₈₉89-bb-P3PT₂₃23), the memory devices showed a write-once-read-many times (WORM) behavior with the switching voltages of −2.6 to −3.3 V and high ON/OFF ratios (10⁵ to 10⁷). The mechanism associated with the memory characteristics was the charge transfer from the P3HT-b-P3PT donor to the PCBM acceptor, which stabilized the charge separated state and retained the high conductance state for a long time during the ON stage. These experimental results provide a new strategy of designing all-conjugated block copolymers for advanced memory device applications.