Interfacing Boron Monophosphide with Molybdenum Disulfide for an Ultrahigh Performance in Thermoelectrics, Two-Dimensional Excitonic Solar Cells, and Nanopiezotronics

A stable ultrathin 2D van der Waals (vdW) heterobilayer, based on the recently synthesized boron monophosphide (BP) and the widely studied molybdenum disulfide (MoS₂), has been systematically explored for the conversion of waste heat, solar energy, and nanomechanical energy into electricity. It shows a gigantic figure of merit (ZT) > 12 (4) for p (n)-type doping at 800 K, which is the highest ever reported till date. At room temperature (300 K), ZT reaches 1.1 (0.3) for p (n)-type doping, which is comparable to experimentally measured ZT = 1.1 on the PbTe-PbSnS₂ nanocomposite at 300 K, while it outweighs the Cu₂Se-CuInSe₂ nanocomposite (ZT = 2.6 at 850 K) and the theoretically calculated ZT = 7 at 600 K on silver halides. Lattice thermal conductivity (κ_l ≈ 49 W m^-1 K^-1) calculated at room temperature is lesser than those of black phosphorene (78 W m^-1 K^-1) and arsenene (61 W m^-1 K^-1). The nearly matched lattice constants in the commensurate lattices of the constituent monolayers help to preserve the direct band gap at the K point in the type II vdW heterobilayer of MoS₂/BP, where BP and MoS₂ serve as donor and acceptor materials, respectively. An ultrahigh carrier mobility of ∼20 × 10³ cm² V^-1 s^-1 is found, which exceeds those of previously reported transition metal dichalcogenide-based vdW heterostructures. The exciton binding energy (0.5 eV) is close to those of MoS₂ (0.54 eV) and C₃N₄ (0.33 eV) single layers. The calculated power conversion efficiency (PCE) in the monolayer MoS₂/BP heterobilayer exceeds 20%. It surpasses the efficiency in MoS₂/p-Si heterojunction solar cells (5.23%) and competes with the theoretically calculated ones, as listed in the manuscript. Furthermore, a high optical absorbance (∼10⁵ cm^-1) of visible light and a small conduction band offset (0.13 eV) make MoS₂/BP very promising in 2D excitonic solar cells. The out-of-plane piezoelectric strain coefficient, d₃₃ ≈ 3.16 pm/V, is found to be enhanced 4-fold (∼14.3 pm/V) upon applying 7% vertical compressive strain on the heterobilayer, which corresponds to ∼1 kbar of hydrostatic pressure. Such a high out-of-plane piezoelectric coefficient, which can tune top-gating effects in ultrathin 2D nanopiezotronics, is a relatively new finding. As BP has been synthesized recently, experimental realization of the multifunctional, versatile MoS₂/BP heterostructure would be highly feasible.

Effect of Preparation Methods on the Tensile, Morphology and Solar Energy Conversion Efficiency of RGO/PMMA Nanocomposites

In this study, reduced graphene oxide (RGO)/polymethyl methacrylate (PMMA) nanocomposites were prepared by employing in situ polymerization and solution blending methods. In terms of mechanical properties, RGO loading increased the Young's modulus but decreased the elongation at break for RGO/PMMA nanocomposites. Tensile strength for solution blended RGO/PMMA nanocomposites increased after adding 0.5 wt % RGO, which was attributed to the good dispersion of RGO in the nanocomposites as evidenced from SEM and TEM. Solar energy conversion efficiency measurement results showed that the optimum concentration of RGO in the RGO/PMMA nanocomposites was found to be 1.0 wt % in order to achieve the maximum solar energy conversion efficiency of 25%. In the present study, the solution blended nanocomposites exhibited better overall properties than in situ polymerized nanocomposites owing to the better dispersion of RGO in solution blending. These findings would contribute to future work in search of higher conversion efficiency using nanocomposites.

Photosynthesis, Light Use Efficiency, and Yield of Reduced-Chlorophyll Soybean Mutants in Field Conditions

Reducing chlorophyll (chl) content may improve the conversion efficiency of absorbed photosynthetically active radiation into biomass and therefore yield in dense monoculture crops by improving light penetration and distribution within the canopy. The effects of reduced chl on leaf and canopy photosynthesis and photosynthetic efficiency were studied in two reportedly robust reduced-chl soybean mutants, Y11y11 and y9y9, in comparison to the wild-type (WT) "Clark" cultivar. Both mutants were characterized during the 2012 growing season whereas only the Y11y11 mutant was characterized during the 2013 growing season. Chl deficiency led to greater rates of leaf-level photosynthesis per absorbed photon early in the growing season when mutant chl content was ∼35% of the WT, but there was no effect on photosynthesis later in the season when mutant leaf chl approached 50% of the WT. Transient benefits of reduced chl at the leaf level did not translate to improvements in canopy-level processes. Reduced pigmentation in these mutants was linked to lower water use efficiency, which may have dampened any photosynthetic benefits of reduced chl, especially since both growing seasons experienced significant drought conditions. These results, while not confirming our hypothesis or an earlier published study in which the Y11y11 mutant significantly outyielded the WT, do demonstrate that soybean significantly overinvests in chl. Despite a >50% chl reduction, there was little negative impact on biomass accumulation or yield, and the small negative effects present were likely due to pleiotropic effects of the mutation. This outcome points to an opportunity to reinvest nitrogen and energy resources that would otherwise be used in pigment-proteins into increasing biochemical photosynthetic capacity, thereby improving canopy photosynthesis and biomass production.

Porphyrin-Based Nanostructures for Photocatalytic Applications

Well-defined organic nanostructures with controllable size and morphology are increasingly exploited in optoelectronic devices. As promising building blocks, porphyrins have demonstrated great potentials in visible-light photocatalytic applications, because of their electrical, optical and catalytic properties. From this perspective, we have summarized the recent significant advances on the design and photocatalytic applications of porphyrin-based nanostructures. The rational strategies, such as texture or crystal modification and interfacial heterostructuring, are described. The applications of the porphyrin-based nanostructures in photocatalytic pollutant degradation and hydrogen evolution are presented. Finally, the ongoing challenges and opportunities for the future development of porphyrin nanostructures in high-quality nanodevices are also proposed.