Department of Chemistry and the Materials Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
J Am Chem Soc. 2011 Feb 9;133(5):1405-18. doi: 10.1021/ja107678m. Epub 2011 Jan 5.
Developing new high-mobility polymeric semiconductors with good processability and excellent device environmental stability is essential for organic electronics. We report the synthesis, characterization, manipulation of charge carrier polarity, and device air stability of a new series of bithiophene-imide (BTI)-based polymers for organic field-effect transistors (OFETs). By increasing the conjugation length of the donor comonomer unit from monothiophene (P1) to bithiophene (P2) to tetrathiophene (P3), the electron transport capacity decreases while the hole transport capacity increases. Compared to the BTI homopolymer P(BTimR) having an electron mobility of 10(-2) cm(2) V(-1) s(-1), copolymer P1 is ambipolar with balanced hole and electron mobilities of ∼10(-4) cm(2) V(-1) s(-1), while P2 and P3 exhibit hole mobilities of ∼10(-3) and ∼10(-2) cm(2) V(-1) s(-1), respectively. The influence of P(BTimR) homopolymer M(n) on film morphology and device performance was also investigated. The high M(n) batch P(BTimR)-H affords more crystalline film microstructures; hence, 3× increased electron mobility (0.038 cm(2) V(-1) s(-1)) over the low M(n) one P(BTimR)-L (0.011 cm(2) V(-1) s(-1)). In a top-gate/bottom-contact OFET architecture, P(BTimR)-H achieves a high electron mobility of 0.14 cm(2) V(-1) s(-1), only slightly lower than that of state-of-the-art n-type polymer semiconductors. However, the high-lying P(BTimR)-H LUMO results in minimal electron transport on exposure to ambient. Copolymer P3 exhibits a hole mobility approaching 0.1 cm(2) V(-1) s(-1) in top-gate OFETs, comparable to or slightly lower than current state-of-the-art p-type polymer semiconductors (0.1-0.6 cm(2) V(-1) s(-1)). Although BTI building block incorporation does not enable air-stable n-type OFET performance for P(BTimR) or P1, it significantly increases the OFET air stability for p-type P2 and P3. Bottom-gate/top-contact and top-gate/bottom-contact P2 and P3 OFETs exhibit excellent stability in the ambient. Thus, P2 and P3 OFET hole mobilities are almost unchanged after 200 days under ambient, which is attributed to their low-lying HOMOs (>0.2 eV lower than that of P3HT), induced by the strong BTI electron-withdrawing capacity. Complementary inverters were fabricated by inkjet patterning of P(BTimR)-H (n-type) and P3b (p-type).
开发具有良好加工性能和优异器件环境稳定性的新型高分子半导体对于有机电子学至关重要。我们报告了一系列新的基于联噻吩-酰亚胺（BTI）的聚合物的合成、表征、电荷载流子极性的操纵以及有机场效应晶体管（OFET）的器件空气稳定性。通过增加给体共聚单体单元的共轭长度，从单噻吩（P1）到联噻吩（P2）再到四噻吩（P3），电子传输能力降低，而空穴传输能力增加。与具有 10(-2) cm(2) V(-1) s(-1) 的电子迁移率的 BTI 均聚物 P(BTimR)相比，共聚物 P1 具有空穴和电子迁移率约为 10(-4) cm(2) V(-1) s(-1) 的双极性，而 P2 和 P3 分别表现出约 10(-3) 和 10(-2) cm(2) V(-1) s(-1) 的空穴迁移率。还研究了 P(BTimR)均聚物 M(n)对薄膜形貌和器件性能的影响。高分子量（M(n)）批次 P(BTimR)-H 提供了更多结晶的薄膜微结构；因此，电子迁移率提高了 3 倍（0.038 cm(2) V(-1) s(-1)），而低分子量（M(n)）批次 P(BTimR)-L（0.011 cm(2) V(-1) s(-1)）则提高了 3 倍。在顶栅/底接触 OFET 结构中，P(BTimR)-H 实现了 0.14 cm(2) V(-1) s(-1)的高电子迁移率，仅略低于最先进的 n 型聚合物半导体。然而，高 P(BTimR)-H 的 LUMO 能级导致在暴露于环境时电子传输最小化。共聚物 P3 在顶栅 OFET 中表现出接近 0.1 cm(2) V(-1) s(-1)的空穴迁移率，与当前最先进的 p 型聚合物半导体（0.1-0.6 cm(2) V(-1) s(-1)）相当或略低。尽管 BTI 结构单元的引入不能使 P(BTimR)或 P1 的 n 型 OFET 性能稳定，但它显著提高了 p 型 P2 和 P3 的 OFET 空气稳定性。底栅/顶接触和顶栅/底接触 P2 和 P3 OFET 在环境中表现出优异的稳定性。因此，P2 和 P3 OFET 空穴迁移率在环境中 200 天后几乎没有变化，这归因于它们的低 HOMO（比 P3HT 低 0.2 eV 以上），这是由 BTI 的强电子吸电子能力引起的。通过喷墨图案化 P(BTimR)-H（n 型）和 P3b（p 型）制造了互补型逆变器。
