Thermoelectricity in single-molecule devices

Harvesting waste energy from heat sources such as electronic devices through exploiting the thermoelectric effect is becoming increasingly attractive as information technique associated devices are now making up over 10% of the worldwide electricity consumption [Mills MP. The cloud begins with coal - big data, big network, big infrastructures and big power; 2013. Available from: https://www.tech-pundit.com/wp-content/uploads/2013/07/CloudBeginsWithCoal.pdf ]. While solid-state thermogenerators have been developed and have shown promising results, their price in addition to other characteristics make them unattractive for a wide use [Zhang Q, Sun Y, Xu W, et al. Organic thermoelectric materials: emerging green energy materials converting heat to electricity directly and efficiently. Adv Mater. 2014;26(40):6829-6851]. Owing to those limitations, molecular structures have emerged as a possible alternative for fabricating cheap, efficient thermogenerators. Single-molecule devices are not prone to the mechanisms that limit the performance of bulk devices and could potentially be used to build ultra-high-efficiency thermoelectric power generators [Venkatasubramanian R, Siivola E, Colpitts T, et al. Thin-film thermoelectric devices with high room-temperature figures of merit. Nature. 2001;413(6856):597-602]. Since the pioneering work by Reddy et al. in measuring single molecules there has been a steady rise in interest in this field [Reddy P, Jang SY, Segalman RA, et al. Thermoelectricity in molecular junctions. Science. 2007;315(5818):1568-1571]. While a molecular device structure allowing for cheap and scalable fabrication as well as exhibiting high efficiency has not been identified yet, there have been intriguing results in theory and experiment, showing what would be necessary to make molecules a viable alternative. Furthermore, molecular electronics has been shown to permit sensing applications and give additional insight into molecular transport. This review was submitted as part of the 2018 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged.