Supporting Information

Anomalous photoluminescence quenching in DIP/MoS2 van der Waals heterostructure: strong charge transfer and modified interface†

Yahya Khana, Sk Md Obaidullaa, Mohammad Rezwan Habiba, Yuhan Kongb, and Mingsheng Xu*a

a School of Information Science and Electronic Engineering (ISEE), State Key Laboratory of

Silicon Materials, Zhejiang University, Hangzhou, Zhejiang 310027, People’s Republic of China

b Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027,

People’s Republic of China

E-mail: msxu@zju.edu.cn

Fig. S1. Illustration of DIP/MoS2 two-step heterostructure fabrication process. (Step (I)): ML-MoS2 r

fabrication on SiO2 substrate by a CVD process, then followed by DIP molecules deposition directly on

MoS2 crystal by organic vapor deposition technique (Step 2).

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Fig. S2. The particle analysis of DIP/SiO2 (230 nm grain size) (a, b) and DIP/ MoS2 (170 nm grain size)

(c, d) particle size estimation of 4 nm DIP on monolayer MoS2.

Fig. S3. UV-Vis spectroscopy of DIP molecules on glass substrate figure (a) the three characteristic peaks of DIP molecules clearly matched with reported values (b) The transition peak of 552 nm was used to calculate the band gap of DIP molecules.

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Fig. S4. UPS analysis.(a)The total UPS spectra of DIP molecules (b) magnified area of Fermi energy as mentioned by light blue shaded region in (a) is ~ 1.55 eV and (c) cut off energy ~ 16.88eV.

To estimate the optical band gap of DIP film, we replotted the UV-vis absorption spectrum of the

DIP film by using the Tauc’s equation of αhv=C (hv−Eg)1/2, [Nanoscale, 2018, 10, 16107]

where α, h, ν, C, and Eg are the absorption coefficient, Planck’s constant, the incident light

frequency, proportionality constant, and the band-gap energy, respectively. Thus, band gap

energy (~2.25 eV) of the DIP film can be estimated from a plot of (αhv)1 /2 versus the photon

energy (hν). Based on the UPS results (Figure S4a, b, c), the HOMO level of the DIP film is

determined to be about 5.89 eV. That is, the two blue lines are the tangents to the curve, which

show the position of the Fermi and the cut-off edge. From the UPS image, we can get the Fermi

energy (EF) is around at 1.55 eV (figure S4 (b)) and the Ecut-off is around at 16.88 eV (figure

S4(c)). It is noted here that we can get the Fermi energy (EF) and Ecut-off by extraplotting the

appropriate values (see light green rectangular box) as indicated by dark green arrows in S4 (a).

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So we can calculate the EHOMO by using the formulaEHOMO=21.22−(16.88−1.55)=5.89 eV .

From UV-vis and UPS measurements, to measure or calculate bandgap LUMO of DIP film can

be estimated about 3.64 eV, from where one can easily draw the hetrostructure band alignment.

The measured DIP molecules energy level is similar to the reported values [1-3] and thus

DIP/MoS2 can be assigned as a type-II heterostructure.

S5: Calculation of coupling strength

E 1−λ γγ E 2− λ = 0 (1)

The coupling strength between two layers in DIP/MoS2 heterojunctions.

As displayed in Figure 4a, b, MoS2 monolayers and DIP show strong photoluminescence at their

respective A-exciton resonances 1.83 eV and 1.73 eV. In DIP/MoS2 heterojunction, the peak of

MoS2 slightly red shifts. The frequency shifts can be attributed to the weak coupling between the

two layers, and the coupling strength γ can be calculated by using a coupled two-system model.

From two individual materials, we have the energies of A-exciton resonances, i.e., E 2=1.83 eV

for MoS2 and E 2=1.73 eV for DIP. In the DIP/MoS2 heterojunction, with the consideration of

interlayer coupling, the energies of observed A-exciton resonances in heterojunction could be

obtained by finding the solutions λ of the following secular determinant. By replacing λ with

1.828 eV andE 2=1.73 eV , for the coupling strength could be estimated by choosing the average

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value ~ 0.26 eV, which is much smaller than the energy of A-exciton resonance in each

standalone monolayer. Where E 2=1.83 eV and E 1=1.822 eV for MoS2 before and after

heterostructure with DIP and E 1=1.73 eV for DIP before heterostructure and after

heterostructure 1.822 eV so the average coupling strength can be calculated as 0.26 eV [4].

Fig. S6. Depth analysis of DIP/MoS2 (a, b) and DIP/SiO2 (c, d)

References

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