Harvesting heat from the environment into electricity has the potential to power Internet-of-things (IoT) sensors, freeing them from cables or batteries and thus making them especially useful for wearable devices. We demonstrate a giant positive thermopower of 17.0 millivolts per degree Kelvin in a flexible, quasi-solid-state, ionic thermoelectric material using synergistic thermodiffusion and thermogalvanic effects. The ionic thermoelectric material is a gelatin matrix modulated with ion providers (KCl, NaCl, and KNO3) for thermodiffusion effect and a redox couple [Fe(CN)64–/Fe(CN)63–] for thermogalvanic effect. A proof-of-concept wearable device consisting of 25 unipolar elements generated more than 2 volts and a peak power of 5 microwatts using body heat. This ionic gelatin shows promise for environmental heat-to-electric energy conversion using ions as energy carriers.

Charge carrier mobility is at the center of organic electronic devices. The strong couplings between electrons and nuclear motions lead to complexities in theoretical description of charge transport, which pose a major challenge for the fundamental understanding and computational design of transport organic materials. This tutorial review describes recent progresses in developing computational tools to assess the carrier mobility in organic molecular semiconductors at the first-principles level. Some rational molecular design strategies for high mobility organic materials are outlined.

The impact of dynamic disorder arising from the thermal fluctuations on the charge transport in organic semiconductors is studied by a multi-scale approach combining molecular dynamics, electronic structure calculations and kinetic Monte Carlo simulations for pentacene crystal of thin-film phase. It is found that for 1-D arrays, such fluctuations severely reduce charge mobility as temperature increases. However, when going from an 1-D array to an 2-D herringbone layer, for a wide range of temperatures, the charge transport property is found to be unaffected by such disorders from our multiscale computational study. And in some extreme cases, when the fluctuations of the hopping integral are even larger than their average values, the dynamic disorders can increase the charge mobility. In addition, we point out that the "band-like" behavior concluded by the experiment can be reproduced by quantum charge transfer involving nuclear vibration tunneling effects within a hopping model.