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Simple elemental thermoelectrics are an ideal platform to demonstrate fundamental physics in materials and develop new strategies for high‐efficiency energy conversion devices. Recently, black phosphorus (BP) is theoretically predicted as a superior thermoelectric candidate, however it meets a great challenge in practical application because of its poor stability. Here, it is reported that the BP phase can be stabilized from 300 to 610 K through creation of a heterojunction structure in Te‐based thermoelectrics, leading to simultaneously enhanced electrical behaviors and reduced thermal conductivity. The peak and average zT values at a temperature range of 300–610 K are increased by 49% and 30% in (Sb, Se, Ge)Te‐BP system, respectively. Maximum zT up to 1.1 at 610 K has been achieved, as the highest value in elemental Te‐based thermoelectrics throughout the measured temperature region. This study clarifies the multiple benefits of engineering a heterojunction structure in independently modulating the coupled parameters, and opens up a pathway searching high performance thermoelectric materials in BP‐based structures. [ABSTRACT FROM AUTHOR]

Because of the unique layered structure, black phosphorus (BP) provides a possibility of relatively independent control in electrical and thermal conductivity for thermoelectrical applications. It is therefore of great interest to realize high-performance BP-based thermoelectrics as flexible non-toxic and ultralight devices in spite of the low energy conversion efficiency and structural instability of the bulk BP. In this work, we systematically study the thermoelectric properties for the two-dimensional BP from mono-layer up to quad-layer by first-principles calculations and Boltzmann transport theory. It can be concluded from the calculations that the thermoelectric performance of BP nanosheets can be effectively optimized by tuning the layer thickness. We reveal that the maximum ZT values at 300 and 500 K can reach up to 0.45 and 0.90 in p -type bi-layer BP along armchair direction, respectively, around 5 times higher than that of the bulk at room temperature. The high performance in bi-layer BP is mainly attributed to its highly anisotropic and degenerate carrier pockets. Accordingly, we further propose that the formation of BP/h-BN heterostructure can enhance ZT up to 1.2 at 500 K, which facilitates the real application of thin BP for flexible and eco-friendly thermoelectrics. • Black phosphorus (BP) nanosheets can be effectively optimized by tuning the layer thickness. • An obviously improved ZT of around 1.0 is predicted in bi-layer BP, compared with the bulk counterpart. • High ZT of bi-layer BP is mainly attributed to its unique anisotropic and highly degenerate band structure. [ABSTRACT FROM AUTHOR]

Clarifying how to design and fabricate an improved material composed by toxic-free and low-cost elements with high thermoelectric conversion efficiency represents one of the most challenging issues in modern materials science. In this work, we apply first-principles calculations and Boltzmann transport theory to study the electronic structure and transport properties on γ -Cu 2 S materials. Our results show that a high thermoelectric figure of merit ZT of 1.2 can be achieved in hole-doped Cu 2 S crystal along b -axis direction at 500 K with an optimal doping of 4.1 × 1019 cm−3. This high thermoelectric property originates from its remarkable valence band structure, which is highly anisotropic combining heavy and light features, and possesses five valence band maxima close to the Fermi level, leading to multivalley transport to enhance Seebeck coefficients and power factors. This work demonstrates hole-doped γ -Cu 2 S is a promising eco-friendly thermoelectric material for large-scale applications. Our exploration on the physical origin of the high thermoelectric efficiency in γ -Cu 2 S can be helpful for further optimizing thermoelectric properties in experiments and sheds strong light on the search or even design of new thermoelectric materials through band engineering. • Low-cost and eco-friendly p -type Cu 2 S could have a high ZT of 1.2 at 500 K. • High ZT of Cu 2 S is due to strong anisotropic and multivalley valence band characters. • Multivalley transport is favorable for thermoelectric properties. [ABSTRACT FROM AUTHOR]