n-Type Quinoidal Oligothiophene-Based Semiconductors for Thin-Film Transistors and Thermoelectrics

Organic electronic devices have gained immense popularity in the last 30 years owing to their increasing performance. Organic thin-film transistors (OTFTs) are one of the basic organic electronic devices with potential industrial applications. Another class of devices called organic thermoelectric (OTE) materials can directly transform waste heat into usable electrical power without causing any pollution. p-Type transistors outperform n-type transistors because the latter requires a lower orbital energy level for efficient electron injection and stable electron transport under ambient conditions. Aromatic building blocks can be utilized in constructing n-type semiconductors. Quinoidal compounds are another promising platform for optoelectronic applications because of their unique properties. Since their discovery in 1970s, quinoidal oligothiophene-based n-type semiconductors have drawn considerable attention as candidates for high-performance n-type semiconductors in OTFTs and OTEs. Herein, the development history of quinoidal oligothiophene-based semiconductors is summarized, with a focus on the molecular design and the influence of structural modification on molecular packing and thus the device performance of the corresponding quinoidal oligothiophene-based semiconductors. Insights on the potential of quinoidal oligothiophenes for high-performance n-type OTFTs and OTEs are also provided.