Type‐I Energy Level Alignment at the PTCDA—Monolayer MoS₂ Interface Promotes Resonance Energy Transfer and Luminescence Enhancement

Abstract

Van der Waals heterostructures consisting of 2D semiconductors and conjugated molecules are of increasing interest because of the prospect of a synergistic enhancement of (opto)electronic properties. In particular, perylenetetracarboxylic dianhydride (PTCDA) on monolayer (ML)‐MoS2 has been identified as promising candidate and a staggered type‐II energy level alignment and excited state interfacial charge transfer have been proposed. In contrast, it is here found with inverse and direct angle resolved photoelectron spectroscopy that PTCDA/ML‐MoS2 supported by insulating sapphire exhibits a straddling type‐I level alignment, with PTCDA having the wider energy gap. Photoluminescence (PL) and sub‐picosecond transient absorption measurements reveal that resonance energy transfer, i.e., electron–hole pair (exciton) transfer, from PTCDA to ML‐MoS2 occurs on a sub‐picosecond time scale. This gives rise to an enhanced PL yield from ML‐MoS2 in the heterostructure and an according overall modulation of the photoresponse. These results underpin the importance of a precise knowledge of the interfacial electronic structure in order to understand excited state dynamics and to devise reliable design strategies for optimized optoelectronic functionality in van der Waals heterostructures.

Donors, acceptors, and a bit of aromatics: electronic interactions of molecular adsorbates on hBN and MoS2 monolayers

“…[1][2][3][4][5][6][7][8][9] Depending on their density on the substrate and on their physico-chemical characteristics, physisorbed moieties can introduce localized electronic states, [10][11][12] dispersive bands, 7 or a combination thereof. [13][14][15] The electronic structure of the interface results from the level alignment between the organic and inorganic components [16][17][18][19][20] and the hybridization between their electronic wave-functions. 15,[21][22][23][24] As both these effects depend on the intrinsic nature of the building blocks, the need for systematic analyses on the electronic structure of hybrid systems are in high demand.…”

Exciton Transfer at Heterointerfaces of MoS2 Monolayers and Fluorescent Molecular Aggregates

“…[ 14 , 15 ] Recent works have shown that combinations of suitable materials allow fabrication of both type‐I and type‐II organic/TMD heterojunctions. [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ] Qiao et al. fabricated heterostructures consisting of MoSe 2 monolayers (bandgap, E g : 1.55 eV) and pentacene ( E g : 1.8 eV).…”

“…fabricated a hybrid structure composed of MoS 2 monolayers ( E g : 2.11 eV) and perylenetetracarboxylic dianhydride ( E g : 2.55 eV), which exhibited a twofold‐enhanced visible‐light PL yield of MoS 2 monolayer. [ 3 ] Since many visible‐light‐fluorescent organic materials are available, [ 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ] efforts to find materials for type‐I organic/TMD heterojunctions and their careful characterizations should deserve considerable attention for both fundamental science and device applications. Also, systematic investigations to study interfacial excitonic behaviors in such hybrid systems should be established.…”

Donors, Acceptors, and a Bit of Aromatics: Electronic Interactions of Molecular Adsorbates on hBN and MoS$_2$ Monolayers

“…[1][2][3][4][5][6][7][8][9] Depending on their density on the substrate and on their physico-chemical characteristics, physisorbed moieties can introduce localized electronic states, [10][11][12] dispersive bands, 7 or a combination thereof. [13][14][15] The electronic structure of the interface results from the level alignment between the organic and inorganic components [16][17][18][19][20] and the hybridization between their electronic wave-functions. 15,[21][22][23][24] As both these effects depend on the intrinsic nature of the building blocks, the need for systematic analyses on the electronic structure of hybrid systems are in high demand.…”