Strong Light-Matter Interactions in Heterostructures of Atomically Thin Films

Abstract

The isolation of various two-dimensional (2D) materials, and the possibility to combine them in vertical stacks, has created a new paradigm in materials science: heterostructures based on 2D crystals. Such a concept has already proven fruitful for a number of electronic applications in the area of ultrathin and flexible devices. Here, we expand the range of such structures to photoactive ones by using semiconducting transition metal dichalcogenides (TMDCs)/graphene stacks. Van Hove singularities in the electronic density of states of TMDC guarantees enhanced light-matter interactions, leading to enhanced photon absorption and electron-hole creation (which are collected in transparent graphene electrodes). This allows development of extremely efficient flexible photovoltaic devices with photoresponsivity above 0.1 ampere per watt (corresponding to an external quantum efficiency of above 30%).

Origin of Indirect Optical Transitions in Few-Layer MoS2, WS2, and WSe2

“…These results suggest that excited electrons will relax to the valence band via K→Γ indirect transition for MoS 2 and WSe 2 whereas Λ→Γ transition is favored for WS 2 (dashed arrows in Figure 1). In real systems, however, excitonic and polaronic effects are expected to play a major role, leading to deviations in the relaxation pathways predicted by the static ground state picture 11,18,21,22,26 . Thus, DFT results may not be directly correlated with experimental observations.…”

“…[1][2][3][4][5][6][7] Correspondingly, stark differences are observed in electrical and optical properties of these materials in the single-to few-layer thickness regime. 5,6,11 The band structure of MoS 2 and its isoelectronic compounds of the group 6 transition metal dichalcogenide (TMD) family, such as MoSe 2 , WS 2 , and WSe 2 , is distinctly different from that of graphene. The conduction band valleys are located at the six corners of the Brillouin zone (K/K' points) and at midpoints along high symmetry lines Γ-K and M-K.…”

Interlayer‐State‐Coupling Dependent Ultrafast Charge Transfer in MoS2/WS2 Bilayers

“…The heterostructures vertically reassembled from different 2D materials form even richer material systems, and thus provide a new platform for investigating new physics12, 13, 14, 15, 16 and exploring new applications 17, 18, 19, 20, 21, 22, 23, 24. The heterostructures of two MX 2 are of particular interests because many of them form type II heterojunctions,25, 26, 27 which facilitate the efficient separation of photoexcited electrons and holes28, 29 and therefore exhibit great potentials in the applications of photodetectors,30, 31 photovoltaic cells,32, 33 and light emitters 34…”

Self‐Assembled Graphene‐Based Architectures and Their Applications

“…The AuCN nanowires could align themselves along the zigzag lattice direction of graphene, which originated from the interaction with the gold atom and the lattice match suggested by the first‐principles calculations. Dangling bonds of damaged graphene,132, 133 vapor‐phase deposition at high temperature,134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148 and intermediate seed materials132, 148, 149, 150 have been used to produce the hybrid of pristine graphene/inorganic nanostructure; however, the formed inorganic nanostructures were randomly oriented or poorly aligned on pristine graphene. This work paves a new way for precisely assembling inorganic nanomaterials on pristine graphene 93, 135, 136, 137, 138, 139…”

“…The enhanced device performance is attributable to a much flatter transmittance curve of the graphene films in the whole spectrum relative to metallic films. Moreover, the high transmittance, along with high conductivity and adjustable work function, makes graphene an appealing choice for uses in transparent conductors,148, 149 photosensitizers,150 and channels for charge transport151 in solar cell applications. In addition, self‐assembled CMG structures could function as electron acceptors or hole‐extraction layers (HEL) for use in polymer solar cells (PSCs).…”