Charge Transfer Exciton and Spin Flipping at Organic–Transition-Metal Dichalcogenide Interfaces

Abstract

Two-dimensional transition-metal dichalcogenides (TMD) can be combined with other materials such as organic small molecules to form hybrid van der Waals heterostructures. Because of different properties possessed by these two materials, the hybrid interface can exhibit properties that cannot be found in either of the materials. In this work, the zinc phthalocyanine (ZnPc)-molybdenum disulfide (MoS) interface is used as a model system to study the charge transfer at these interfaces. It is found that the optically excited singlet exciton in ZnPc transfers its electron to MoS in 80 fs after photoexcitation to form a charge transfer exciton. However, back electron transfer occurs on the time scale of ∼1-100 ps, which results in the formation of a triplet exciton in the ZnPc layer. This relatively fast singlet-triplet transition is feasible because of the large singlet-triplet splitting in organic materials and the strong spin-orbit coupling in TMD crystals. The back electron transfer would reduce the yield of free carrier generation at the heterojunction if it is not avoided. On the other hand, the spin-selective back electron transfer could be used to manipulate electron spin in hybrid electronic devices.

Spontaneous Exciton Dissociation at Organic Semiconductor Interfaces Facilitated by the Orientation of the Delocalized Electron–Hole Wavefunction

“…While we will focus on the dissociation of the CT exciton, we note that evidences for the initial electron transfer process from ZnPc to F 8 ZnPc can be found in the spectra obtained from the 1 nm-ZnPc on F 8 ZnPc sample. Similar to other donor-acceptor interfaces that we have studied using TR-TPPE, [29,[54][55][56] we observe a fast quenching in the ZnPc's S 1 signal on the 100-fs timescale (Section S4, Supporting Information) that is resulted from the CT from ZnPc to F 8 ZnPc.…”

Molecular Functionalization of Two‐Dimensional MoS2 Nanosheets

“…[36] This last differencep ossibly arises from the neutralization of excesse lectrons presenta long the nanosheets, rather than Scheme2.Doping am echanically exfoliated monolayer MoS 2 with electron donors (TCNQ or F 4 TCNQ) results in the de-stabilization of the tightlyb ound trions( quasiparticles consisting of one positivea nd two negativecharges) and efficient excitonrecombination, namely enhancemento fthe photoluminescence emission. [38] Phthalocyanines are chemically stable dyes, capable of hostingag reat variety of metal cations. Annealing exfoliated MoS 2 at 250 8Ci na ir was found to deplete the abundante lectrons present onto the surface of nanosheets.…”

“…As expected, photoexcited ZnPc transferred electrons to MoS 2 on at ime scale of 80 fs;h owever,abackelectron transfer from the MoS 2 was found to occur,f orming a ZnPc triple exciton, which eventually reduced the yield of free carrier generation at the p-n junction. [38] Phthalocyanines are chemically stable dyes, capable of hostingag reat variety of metal cations. Moreover,since phthalocyanines can be customdesigned so as to carry electron-donating or -withdrawing groups,c opper-, iron-, platinum-, and sodium-chelated sulfonated phthalocyanines were deposited ontom echanicallye x-foliatedM oS 2 monolayers and the doping effects were probed.…”

Engineering 3D perovskites for photon interconversion applications

“…However, the largest drawback of these triplet states is that their direct optical excitation is 'spin-forbidden' and thus, it is difficult to directly excite them. To circumvent this issue, researchers have turned to a wide variety of triplet sensitizers ranging from metal-organic complexes with high spin-orbit coupling [5][6][7][8][9][10][11][12][13], semiconductor quantum dots [14][15][16][17][18] and more recently, lead halide perovskites [19][20][21][22][23][24][25][26][27] and other spin-mixing materials such as transition metal dichalcogenides [28,29]. While each of these approaches bears their own benefit, we will in the following focus on the emerging field of three-dimensional (3D) perovskite-sensitized UC.…”