Low-cost and sustainable organic thermoelectrics based on low-dimensional molecular metals

More than 70 % of the primary energy consumed world-wide is wasted, mostly as heat below 100 °C[1]. Thermoelectric generators may convert a substantial amount of this energy into electrical power but high production costs and scarcity of efficient thermoelectric materials operating in this temperature regime have limited large-scale applications so far. Recently, conducting polymers have been proposed as potential candidates to meet these challenges showing appreciable low-temperature thermoelectric performance, but unfortunately suffering from low electrical conductivity due to inherent disorder[2–5]. Herein, crystalline low-dimensional molecular metals are demonstrated as an alternative class of thermoelectric materials combining the advantages of low weight, chemical variety, sustainability and high charge carrier mobility with reduced electronic dimensionality. For the first time determining all relevant thermoelectric quantities on individual organic crystals of both, p-type TTT2I3 and n-type DCNQI2Cu conductors, high power factors and promising figures of merit surpassing values of zT≥0.15 below 40 K are disclosed in this study. The cost-defining power output per active area of a prototypical, all-organic TEG takes unprecedented values of ~mW/cm2 at RT. Violation of the Wiedemann-Franz law and phonon drag effects emerge from the materials’ low-dimensionality and are expected to deliver further thermoelectric enhancement feasible in near future