Supertransport of excitons in atomically thin organic semiconductors at the 2D quantum limit

Abstract

Long-range and fast transport of coherent excitons is important for the development of high-speed excitonic circuits and quantum computing applications. However, most of these coherent excitons have only been observed in some low-dimensional semiconductors when coupled with cavities, as there are large inhomogeneous broadening and dephasing effects on the transport of excitons in their native states in materials. Here, by confining coherent excitons at the 2D quantum limit, we first observed molecular aggregation-enabled ‘supertransport’ of excitons in atomically thin two-dimensional (2D) organic semiconductors between coherent states, with a measured high effective exciton diffusion coefficient of ~346.9 cm2/s at room temperature. This value is one to several orders of magnitude higher than the values reported for other organic molecular aggregates and low-dimensional inorganic materials. Without coupling to any optical cavities, the monolayer pentacene sample, a very clean 2D quantum system (~1.2 nm thick) with high crystallinity (J-type aggregation) and minimal interfacial states, showed superradiant emission from Frenkel excitons, which was experimentally confirmed by the temperature-dependent photoluminescence (PL) emission, highly enhanced radiative decay rate, significantly narrowed PL peak width and strongly directional in-plane emission. The coherence in monolayer pentacene samples was observed to be delocalised over ~135 molecules, which is significantly larger than the values (a few molecules) observed for other organic thin films. In addition, the supertransport of excitons in monolayer pentacene samples showed highly anisotropic behaviour. Our results pave the way for the development of future high-speed excitonic circuits, fast OLEDs, and other optoelectronic devices.

Retracted: Emerging 2D MXene/Organic Heterostructures for Future Nanodevices

“…Recently, anisotropic excitonic emission has also been demonstrated in monolayer pentacene. [ 89 ] Indeed, many recent research progress suggest that 2D organic semiconductors have unique charge–phonon interactions where phonons temporarily interrupt the band structure causing a transient localization of charge carriers, [ 90 ] which is believed to causes such anisotropic transport. It is also important to note that presence of tiny narrow cracks in the lattice can also promote intrinsic anisotropic behavior.…”

“…It is also important to note that presence of tiny narrow cracks in the lattice can also promote intrinsic anisotropic behavior. [ 91 ] Furthermore, theoretical studies in recently observed anisotropic excitonic emission in monolayer pentacene, [ 89 ] predicted the strong directional transition dipole moment (TDM) on such ultrathin regime. Such TDM is expected to lead to in‐plane anisotropic emission.…”

Effectively Enhanced Broadband Phototransistors Based on Multilayer WSe2/Pentacene

“…Besides, excitons from singlet or triplet states could diffuse into organic semiconductors, and the possible exciton diffusion lengths vary from a few nm to µm depending on the materials. [10,11] Pentacene (C 22 H 14 ) is a p-type organic semiconductor consisting of five benzene rings linearly connected. Pentacene exhibits significant absorption under broad spectral lights and offers considerably long exciton diffusion lengths around 0.55 µm.…”

“…Pentacene exhibits significant absorption under broad spectral lights and offers considerably long exciton diffusion lengths around 0.55 µm. [11] It can be directly grown on WSe 2 at low temperatures by a concise evaporation process without any undesirable electronic deformations. The WSe 2 and pentacene's hybrid structure could potentially enhance optoelectronic properties in multilayer WSe 2 .Herein, we've designed and demonstrated the multilayer WSe 2 /pentacene-based broadband phototransistors.…”

2D Materials and Heterostructures at Extreme Pressure

“…[58] In the past decade, a majority of 2D ultrathin materials involving transition metal dichalcogenides (TMDs, e.g., MoS 2 , MoSe 2 , WSe 2 , WS 2 , TiS 2 , TaS 2 , etc. ), [49,[59][60][61] BN, [21][22][23][24][25][26]35,[62][63][64][65][66][67][68][69][70][71] BP, [72][73][74][75][76][77][78][79][80][81][82][83][84] 2D organic crystals (e.g., 2D small molecular and polymers), [85][86][87][88][89][90][91][92][93][94][95] 2D perovskites, [96][97][98][99]…”