Across the global energy economy only about 1/3 of primary energy is converted into useful energy services, the other 2/3 are wasted as heat in the various industrial, transportation, residential energy conversion and electricity generation processes. Given the urgent need for transitioning to a zero-carbon energy supply in order to mitigate dangerous consequences of climate change a waste of energy on this scale is scandalous. Thermoelectric waste-heat-to-electricity conversion could offer a potential solution but the performance of thermoelectric materials is currently insufficient, particularly for the majority of heat that is generated at low heat source temperatures below 300-400°C. Based on a recent scientific breakthrough I have become convinced that the unique characteristics of molecular, organic semiconductors (OSCs) could make them ideal, low-temperature thermoelectric materials, but the thermoelectric physics of this class of soft materials with complex microstructures and strong electron-phonon coupling remains as yet largely unexplored and poorly understood. The aim of this proposal is (a) to develop novel experimental methods for the nanoscale characterisation of the thermoelectric properties of a very promising new generation of molecular thermoelectric materials, (b) to achieve a clear fundamental understanding of their thermoelectric physics and how thermoelectric transport coefficients can be decoupled and enhanced independently in these materials and (c) to translate this into the design of high performance molecular thermoelectric materials with unprecedented performance ZT > 2-3 at temperatures < 300-400°C. This is a fundamental and interdisciplinary, high-risk research programme stretching across theory, condensed matter physics, chemistry and materials science as well device engineering. If successful the project could make a significant contribution to improved energy efficiency and a successful transition to a zero-carbon energy economy.