Fundamental Thermoelectric Properties in Organic Heterojunctions from Molecular to Thin‐Film and Hybrid Designs

Abstract Organic heterojunctions have become a unique platform to explore superior thermoelectric performance based on the fundamental possibilities of separately controlling electrical and thermal transport through interfaces structured at different length scales. Particularly, the “heterojunctions” present artificially made components, in addition to each component used to form heterojunctions, to further control electrical and thermal conductions toward developing high‐performance thermoelectrics. Potentially, in organic heterojunctions, the different components (organic–organic, organic–inorganic) possess low thermal and high electrical conductivities, which present the necessary conditions for developing high thermoelectric actions. Furthermore, organic heterojunctions provide an opportunity to form electrically conductive but thermally resistive interfaces between different components at different length scales from molecular to thin‐film and hybrid designs, functioning as a third component, upon combing two components. In particular, the interface can be facilely tuned toward ultimately separating electrical and thermal conduction by rationally selecting electric, polarization and thermal parameters. In this Review, the fundamental thermoelectric properties of organic heterojunctions from molecular to thin‐film and hybrid designs are presented. The thermoelectric performances enhanced by interface effects are also highlighted. Finally, the outlook for the further thermoelectric developments is discussed.