Interfacing
Boron
Monophosphide with Molybdenum Disulfide for an Ultrahigh Performance
in Thermoelectrics, Two-Dimensional
Excitonic Solar Cells, and Nanopiezotronics
posted on 2020-01-05, 18:43authored byManish
Kumar Mohanta, Ashima Rawat, Nityasagar Jena, Dimple, Raihan Ahammed, Abir De Sarkar
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 (κl ≈ 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.