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Thermoelectric materials can directly convert waste heat into electrical energy and will play a significant role in future energy management. Herein, we have achieved improved thermoelectric performance in p-type Te-free AgSb 1Àx Cd x Se 2 (x ¼ 0.02-0.06) system. Simple doping of Cd 2+ in the Sb 3+ sublattice increases the carrier concentration, resulting in enhanced electrical conductivity in AgSb 1Àx Cd x Se 2 compared to the pristine AgSbSe 2 . Improved electrical transport and ultra low thermal conductivity give rise to a high thermoelectric figure of merit, ZT, of $1 at $640 K in AgSb 0.98 Cd 0.02 Se 2 , which is similar to the traditional market based expensive and scarce metal tellurides.Thermoelectric materials allow direct conversion between thermal and electrical energy and provide an alternative path for power generation. Over the past few decades, the exploration of high-performance thermoelectric materials has attracted ever-growing attention both from the energy and environmental perspectives with a view to commercial applications. The efficiency of the thermoelectric materials is dened by dimensionless thermoelectric gure of merit, ZT ¼ sS 2 T/(k el + k latt ), where s, S, T, k el and k lat are the electrical conductivity, Seebeck coefficient, temperature, electronic thermal conductivity and lattice thermal conductivity, respectively. 1-9 However, development of high performance materials is a great challenge due to the interdependency of S, s and k. In order to increase ZT, the materials need to possess either high power factor (sS 2 ) or low thermal conductivity (k), or both at the same time. 1-9 To develop high performance materials, various innovative approaches have been identied in the recent years. Convergence of multiple valence bands through proper carrier engineering is an efficient way to improve the power factor (sS 2 ) of the thermoelectric materials. 10 Introduction of resonance level in the electronic band has been proven successful to enhance the S. 11 Second phase endotaxial nanostructuring 6 and most recently all-length scale phonon scattering 7 have been demonstrated to be efficient routes to enhance the ZT through significant reduction of the k lat . Alternatively, low k lat has also been achieved in the bulk semiconductor due to strong anharmonicity of the bonding arrangements. 12,13Among the high ZT materials, PbTe is the most efficient for power generation applications at high temperature, 2-8 whereas Bi 2 Te 3 based materials are well known for thermoelectric refrigeration. 14,15 Beyond these traditional materials, cubic I-V-VI 2 (where I ¼ Cu, Ag, Au or alkali metal; V ¼ As, Sb, Bi; and VI ¼ S, Se, Te) semiconductors are well known for their intrinsically low k lat due to the strong anharmonicity of the bonding arrangements. 12,13 Among them, p-type AgSbTe 2 is renowned for excellent thermoelectric performance. 16-19 Nanostructured alloys of GeTe (TAGS) 20 and PbTe (LAST-m) 21 with AgSbTe 2 showed remarkable ZT values of $1.5 at 750 K and $1.8 at 800 K, respectively. How...

Layered intergrowth compounds in the homologous Pbm Bi2n Te3n+m family are interesting because they are examples of natural heterostructures. We present a simple solution-based synthesis of two-dimensional nanosheets of PbBi2 Te4 , Pb2 Bi2 Te5 , and PbBi6 Te10 layered intergrowth compounds, which are members of the Pbm Bi2n Te3n+m [that is, (PbTe)m (Bi2 Te3 )n ] homologous series. Few-layer nanosheets exhibit narrow optical band gaps (0.25-0.7 eV) with semiconducting electronic-transport properties.

Layered lead bismuth selenide, PbBi2Se4, an intergrowth compound of PbSe (rocksalt) and Bi2Se3 (hexagonal), is a topological insulator in the bulk phase. We present a simple solution based synthesis of two dimensional (2D) few seven atomic (septuple) layered PbBi2Se4 nanosheets (4-7 nm thick) for the first time. The excellent electrical transport in ultrathin PbBi2Se4 is attributed to the presence of dominant surface states that offer high electrical mobility (∼153 cm(2) V(-1) s(-1)) and scattering resistant carriers. Ultrathin 3-5 SLs PbBi2Se4 shows an n-type semiconducting behaviour with a band gap of ∼0.6 eV, which is confirmed by optical spectroscopy and thermopower measurements.

Electronic grade semiconductor films have been obtained via the sintering of solution processed PbS and PbSe nanocrystals at room temperature. Prior attempts to achieve similar films required the sintering of nanocrystals at higher temperatures (>350 °C), which inhibits the processing of such films on a flexible polymer substrate, and it is also expensive. We reduced the sintering temperature by employing two important strategies: (i) use of ligand-free nanocrystals and (ii) oriented attachment of nanocrystals. Colloidal ligand-free PbS and PbSe nanocrystals were synthesized at 70 °C with high yield (∼70%). However, these nanocrystals start to agglomerate with time in formamide, and upon the removal of the solvation energy, nanocrystals undergo oriented attachment, forming larger elongated crystals. PbS and PbSe nanocrystal films made on both glass and flexible substrates at room temperature exhibit Ohmic behavior with optimum DC conductivities of 0.03 S m(-1) and 0.08 S m(-1), respectively. Mild annealing of the films at 150 °C increases the conductivity values to 1.1 S m(-1) and 137 S m(-1) for PbS and PbSe nanocrystal films, respectively. AC impedance was measured to distinguish the contributions from grain and grain boundaries to the charge transport mechanism. Charge transport properties remain similar after the repeated bending of the film on a flexible polymer substrate. Reasonably high thermoelectric Seebeck coefficients of 600 μV K(-1) and 335 μV K(-1) for PbS and PbSe nanocrystal pellets, respectively, were obtained at room temperature.