Abstract
Expression of energy filtering to boost thermoelectric performance through grain boundary engineering utilising graphene.
Highlights
Optimizing the thermoelectric properties in a material has always been a balancing act of inversely corelated material’s properties
In Te doped Mg3Sb2 we show the introduction of graphene nanoplatelets (GNP) increases the interfacial thermal resistance of grain boundaries, enhancing the contribution of the interfacial Seebeck coefficient arising from grain boundaries to the overall Seebeck coefficient
Using Mg3Sb2 as an example material, we experimentally demonstrate a grain boundary engineering approach to realize the benefit of energy filtering, through the addition of graphene
Summary
Filtering approach surmises that these low energy electrons can be preferentially blocked by an energy barrier, resulting in an increase in thermopower (the magnitude of Seebeck coefficient). Mg3Sb2 is an example of a material with charged grain boundaries that lead to an energy offset (DE) between the conduction band minimum (CBM) in the grain and that of the grain boundary (Fig. 1a).[10] This physical picture is essentially the same as what is predicted to increase a material’s Seebeck coefficient through electron filtering.[11,12] instead of benefitting from grain boundaries, previous reports on n-type Mg3Sb1.5Bi0.5 have found significantly lower thermoelectric performance with smaller grains This has been traced to the added electrical resistance at grain boundaries where the effect of grain boundaries[10] on the lattice thermal conductivity and Seebeck coefficient was reported as largely negligible.[19,20]. This in turn leads to an increased expression of the interfacial Seebeck coefficient arising from grain boundaries that adds to the total Seebeck coefficient, which enhances the material’s maximum power factor and figure of merit zT (Fig. 2)
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