Reliable Piezoelectricity in Bilayer WSe₂ for Piezoelectric Nanogenerators

Abstract

Recently, piezoelectricity has been observed in 2D atomically thin materials, such as hexagonal-boron nitride, graphene, and transition metal dichalcogenides (TMDs). Specifically, exfoliated monolayer MoS exhibits a high piezoelectricity that is comparable to that of traditional piezoelectric materials. However, monolayer TMD materials are not regarded as suitable for actual piezoelectric devices due to their insufficient mechanical durability for sustained operation while Bernal-stacked bilayer TMD materials lose noncentrosymmetry and consequently piezoelectricity. Here, it is shown that WSe bilayers fabricated via turbostratic stacking have reliable piezoelectric properties that cannot be obtained from a mechanically exfoliated WSe bilayer with Bernal stacking. Turbostratic stacking refers to the transfer of each chemical vapor deposition (CVD)-grown WSe monolayer to allow for an increase in degrees of freedom in the bilayer symmetry, leading to noncentrosymmetry in the bilayers. In contrast, CVD-grown WSe bilayers exhibit very weak piezoelectricity because of the energetics and crystallographic orientation. The flexible piezoelectric WSe bilayers exhibit a prominent mechanical durability of up to 0.95% of strain as well as reliable energy harvesting performance, which is adequate to drive a small liquid crystal display without external energy sources, in contrast to monolayer WSe for which the device performance becomes degraded above a strain of 0.63%.

Hybrid lead-free polymer-based nanocomposites with improved piezoelectric response for biomedical energy-harvesting applications: A review

“…Various kinds of PVDF-based and PVDF-ceramic-based micro/nanostructures, such as porous films [164,165], electrospun NF mats [23,26,166,167], and trigonal line-shaped and pyramidshaped films [168], have demonstrated enhanced output compared to conventional bulk films, as have nanowires (pillars) prepared via nanoconfinement in AAO [169,170]. Table 3 summarises the main output parameters of various structured polymer-based composites.…”

“…In addition to the above-mentioned structurisation methods, micropatterned polymer films, such as films with trigonal line-shaped and pyramid-shaped micropatterns, have also been fabricated [168]. The electric power output from piezoelectric generators based on structured hybrid composites is greater than that of the pristine polymer-based PENGs and PEMGs; however, the preparation of polymer composite-based PENGs/PEMGs still presents problems, such as a complex fabrication process, poor reproducibility, non-uniform power output, low economic effectiveness, and the difficulty of controlling the interface between the inorganic nanostructures and the polymer matrix.…”

Hybrid Energy Harvesters: Toward Sustainable Energy Harvesting

“…There are various energy harvesting systems, such as piezoelectric, triboelectric, thermoelectric, pyroelectric, photovoltaic, and water evaporation‐based energy harvesting systems and those using green energy sources such as solar, wind, wave, heat, and vibrations. These renewable energy harvesting systems have been receiving great attention in the field of research into renewable and sustainable energy harvesters (EHs) to realize self‐powering smart WSN systems and self‐charging electronics . The output performance of energy harvesting systems has rapidly improved, and WSN systems and energy harvesting systems have been combined.…”

A high performance flexible two dimensional vertically aligned ZnO nanodisc based piezoelectric nanogenerator via surface passivation

“…17 Recently, 2D materials such as MoS 2 nanosheet and bilayer WSe 2 based piezoelectric nanogenerators have also been reported. [18][19][20][21] To improve the power efficiency of ZnO based nanogenerators, hybridization with a p-type polymer such as poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) was employed. 22,23 Moreover, doping transition and alkali elements in ZnO also increased the piezoelectric charge coefficient and nanogenerator performance.…”