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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]

Black phosphorus (BP) has emerged as a promising thermoelectric candidate because of its strong electronic and thermal anisotropy, suggesting a large σ/κ ratio can be realized by controlling carrier transport orientation for a potentially high ZT. Nevertheless, to date, low conversion efficiency (ZT ≈0.08, 300 K) and poor stability of BP remain the major issues that have hampered its practical applications. This work reports a material family in simple composition XP7, XP3, and XP (X = N, As, Sb, Bi) with high‐performance thermoelectric properties by first‐principles calculations. Strikingly, an ultrahigh ZT up to 1.21 at 300 K is achieved in p‐type BiP7 with an optimal carrier concentration of 5.48 × 1019 cm−3 and ZT in n‐type NP3 can reach up to ≈0.87 at the electron concentration of 3.67 × 1019 cm−3 along the zigzag direction, owing to their enhanced density of states and multivalley band structures around the Fermi level through the resonant effects of VA guest and host atoms. Additionally, the calculations demonstrate further improvement in thermoelectric performance of pristine BP by ≈4.8 and 4.5 times at 800 K in p‐type NP and n‐type NP3, respectively. Considering the high stability, current results indicate that N–P based systems are highly promising for novel metal‐free, nontoxic, and ultralight thermoelectrics. [ABSTRACT FROM AUTHOR]