Nanoengineering thermoelectrics for 21st century: Energy harvesting and other trends in the field

In the beginning of the 21st century, the world is facing the major challenge of finding energy sources to satisfy the ever-increasing energy consumption while preserving the environment. In the race to search alternative energy sources, thermoelectric generators are called to play their role in the improvement of the efficiency of the actual energy system by harvesting nowadays wasted heat. This review deals with the novel aspects of nano-structuring of thermoelectric materials, from the so called 3D nanobulk materials down to the incorporation of 0D quantum dots in thermoelectric structures. The improvement in the efficiency of nanoengineering thermoelectrics benefits mainly from the reduction in the thermal conductivity. Other promising trends in thermoelectricity are also reviewed, such as, novel nano-structures, trending materials (polymers, thermionic materials or Zintl phases), spin caloritronics, thermoelectricity in atomic and molecular junctions, or recent developments in theoretical calculations. Finally the review ends with a brief review on recent thermoelectric devices.