Correlation of Molecular Structure and Charge Transport Properties: A Case Study in Naphthalenediimide–Based Copolymer Semiconductors

Journal article, 2018

Recent development of donor–acceptor (D–A) structure copolymers has led to the remarkable enhancement of mobility over 10 cm2(V s)−1in organic semiconductors. Despite these achievements, a thorough understanding of the correlation between molecular structure and charge transport properties is still not achieved. With this goal in mind, the electrical properties of three copolymers based on the naphthalenediimide (NDI) acceptor with different donor units are compared, and the effect of increasing donor length on the electronic structure of semiconductors and the resulting charge transport performance is studied. Structural and morphological characterizations are done to reveal the macro transport properties of the semiconductor films. Then, electrical measurements of the field-effect transistors at variable temperatures are carried out to probe the charge transport property of the semiconductor films. Overall, it is found that the increasing of the donor length from one to three thiophene units would reduce the energetic disorder in the semiconductor films. Meanwhile, the electron cloud overlap between acceptor units would be weakened, which is detrimental to electron transport. Thus, a trading-off between energetic disorder and electron cloud overlap is critical for achieving high mobility in this NDI–based copolymer system.