Executive Summary : | Thermoelectric conversion of heat energy to electrical energy is governed by the dimensionless figure of merit, ZT = Sigma X (S²) T /(k_lat + k_el), where 'Sigma' is electrical conductivity, S is Seebeck coefficient, k-lat is lattice thermal conductivity, k-el is electronic thermal conductivity, and T is temperature in Kelvin. The bottleneck in achieving high ZT is generally the complex interdependency in between the thermoelectric parameters. Lattice thermal conductivity being the only independent parameter in the equation makes it indispensable to reduce in order achieve high thermoelectric efficiency.
2D Layered materials are gathering considerable interest in the field of thermoelectrics due to their unique structural identity. The presence of heterogeneous bonding environment within each layer lead to anisotropic transport properties. SnSe being a layered compound recently showed impressive ZT in single crystalline form. The compounds not only possess high anisotropic carrier mobility but also intrinsically ultralow lattice thermal conductivity. The presence of such innate low lattice thermal conductivity is the governing parameter for such high ZT values. Other 2D layered compounds such as SnSe2, GeSe, SnS, GeS, BiSe and SbSe are also slowly gathering importance in the scientific community and are touted to play an important role for future high-performance thermoelectric materials. We propose several innovative routes to furnish and optimize the performance of these layered 2D chalcogenides via (a) Lattice anharmonicity and anisotropy in layered IV-VI chalcogenides - reducing the lattice thermal conductivity of the 2D materials which show considerable lattice anharmonicity and anistropy; (b) Modulation of electronic structure and thermoelectric properties- tuning of electronic transport properties via adequate doping and co-doping; (c) Furnishing of layered intergrowth compounds – such as [i.e. (MQ)m(E2Q3)n; M = Ge/Sn/Pb; E = Sb/Bi; Q = S/Se/Te] which may possess low lattice thermal conductivity due to natural van der Waal heterostructure nature and exotic electronic structure such as in topological quantum materials. Several exotic 2D layered compounds in the homologues series of (Bi2)m(Bi2Se3)n and (Bi2)m(Bi2Te3)n can also be explored under this project. |