The unusual electronic structure of ambipolar dicyanovinyl-substituted diketopyrrolopyrrole derivatives
作者:A. Riaño、P. Mayorga Burrezo、M. J. Mancheño、A. Timalsina、J. Smith、A. Facchetti、T. J. Marks、J. T. López Navarrete、J. L. Segura、J. Casado、R. Ponce Ortiz
DOI:10.1039/c4tc00714j
日期:——
We have synthesized two novel dicyanovinylene-substituted DPP–oligothiophene semiconductors, DPP-4T-2DCV and 2DPP-6T-2DCV. In these materials, the combination of an extended oligothiophene conjugated skeleton with the strong electron-withdrawing DPP–dicyanovinylene groups results in semiconductors exhibiting ambipolar TFT response with reasonably balanced electron and hole mobilities of up to 0.16 cm2 V−1 s−1 and 0.02 cm2 V−1 s−1, respectively. Furthermore, no thermal annealing of the semiconductors is necessary to afford high mobility, making them ideal candidates for low cost fabrication of devices on inexpensive plastic foils. Analysis of the molecular and electronic structures by means of electronic and vibrational spectroscopy techniques, electrochemistry and DFT calculations highlights a unique electronic scenario in these semiconductors, where the external cyano groups are isolated from the π-conjugated core. The appearance of these unusual π-systems explains the similar electron mobilities recorded for both DPP-4T-2DCV and 2DPP-6T-2DCV, despite their different skeletal dimensions. Furthermore, it also supports the appearance of moderately balanced hole and electron mobilities in semiconductors with such large accumulation of acceptor units. Transient spectroscopy measurements indicate the appearance of triplet excited state species, which may be related to the semiconductors' low performances in OPVs, due to the intrusion of triplets in the carrier formation process.
我们合成了两种新型双氰基乙烯基取代 DPP-寡噻吩半导体:DPP-4T-2DCV 和 2DPP-6T-2DCV。在这些材料中,延伸的低聚噻吩共轭骨架与强电子吸收性的 DPP-双氰基乙烯基团相结合,使半导体呈现伏极性 TFT 响应,电子和空穴迁移率相当平衡,分别高达 0.16 cm2 V-1 s-1 和 0.02 cm2 V-1 s-1。此外,无需对半导体进行热退火处理即可获得高迁移率,这使它们成为在廉价塑料薄膜上低成本制造器件的理想候选材料。通过电子和振动光谱技术、电化学和 DFT 计算对分子结构和电子结构进行分析,突出显示了这些半导体中独特的电子情况,即外部氰基与π共轭核心隔离。这些不寻常的 π 系统的出现解释了 DPP-4T-2DCV 和 2DPP-6T-2DCV 虽然骨架尺寸不同,但电子迁移率却相似的原因。此外,它还支持在具有如此大的受体单元积累的半导体中出现适度平衡的空穴和电子迁移率。瞬态光谱测量结果表明,在载流子形成过程中出现了三重激发态物种,这可能与半导体在 OPV 中的低性能有关。