Supplementary information. Defect Engineering. Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and

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1 Supplementary information Achieving Ultrafast Hole Transfer at the Monolayer MoS 2 and CH 3 NH 3 PbI 3 Perovskite Interface by Defect Engineering Bo Peng,,, Guannan Yu ѫ,, Yawen Zhao Э,, Qiang Xu ѫ, Guichuan Xing ѫ, Xinfeng Liu ѫ, Deyi Fu, Bo Liu, Jun Rong Sherman Tan, Wei Tang, Haipeng Lu, Jianliang Xie, Longjiang Deng, Tze Chien Sum ѫ, * and Kian Ping Loh, * Department of Chemistry and Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 3 Science Drive 3, Singapore National Engineering Research Center of Electromagnetic Radiation Control Materials and State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu , China ѫ School of Physical & Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore CAS Center for Excellence in Nanoscience & CAS Key Laboratory of Standardization and Measurement for Nanotechnology, National Center for Nanoscience and Technology, Beijing , China Э China Academy of Engineering Physics, P.O.Box , Mianyang, , Sichuan, China 1

2 These authors contributed equally to this work * To whom correspondence should be addressed. address: tzechien@ntu.edu.sg and chmlohkp@nus.edu.sg S1. Determination of band alignment in a MoS 2 /CH 3 NH 3 PbI 3 heterostructure S2. Thickness measurement of CH 3 NH 3 PbI 3 perovskite films S3. System Response Deconvolution S4. Charge Transfer Modeling S5. Triangular vacancy clusters and defect agglomerations S6. Calculation Method S7. Topography images of MoS 2 monolayer before and after O 2 plasma S8. Ultrafast hole transfer between vacancy-engineered MoS 2 monolayer and CH 3 NH 3 PbI 3 upon excitation at 2.48 ev S9. Experimental parameters of mild O 2 plasma treatment on MoS 2 monolayer 2

3 CPS CPS S1. Determination of band alignment in a MoS 2 /CH 3 NH 3 PbI 3 heterostructure In our studies, the valence band maximum (VBM) of CH 3 NH 3 PbI 3 were investigated by Ultraviolet Photoelectron Spectroscopy (UPS). UPS was performed in a UHV analysis chamber (base pressure 5 x mbar) equipped with SPECS UVS 300 source and SPECS TMM304 toroidal mirror monochromator. The UPS spectra were recorded using monochromated He I radiation (21.2eV). The photoelectrons were analyzed by SPECS PHOIBOS 150 Hemispherical Energy Analyzer and Delay Line Detector 3D-DLD UPS binding energies were calibrated and referenced to the Fermi level of a gold foil. Secondary Electron Cut-Off (SECO) determination was measured with a negative bias of 3V on the sample. Our experimental data established that the VBM of CH 3 NH 3 PbI 3 perovskite films is at ev. The exciton binding energy of CH 3 NH 3 PbI 3 is ~29 mev. 1 Theoretically, the VBM and CBM of MoS 2 monolayer are at 6.28 and ev (Fig. 1a), respectively. 2 Considering the optical bandgap and exciton binding energy, the MoS 2 /CH 3 NH 3 PbI 3 layers are predicted to form a type-i heterostructure where both CBM and VBM are at CH 3 NH 3 PbI 3. a MAPI 2.0x10 4 VB onset: 1.40 ev 1.5x x x10 3 b 1.2x10 6 MAPI 1.0x10 6 WF: 4.39 ev 8.0x x x x Binding Energy (ev) Binding Energy (ev) Figure S1. The valance band onset and work function (WF) of CH 3 NH 3 PbI 3 (a, b). 3

4 Z (nm) S2. Thickness measurement of CH 3 NH 3 PbI 3 perovskite films The MoS 2 /CH 3 NH 3 PbI 3 heterostructure was prepared by spin-coating a CH 3 NH 3 PbI 3 layer on the MoS 2 flake. The thickness analyses of CH 3 NH3PbI 3 perovskite films were performed using a BRUKER Dimension FastScan AFM. The thickness of the studied films was determined to ~30 nm. MoS 2 monolayer was first mechanically exfoliated from a bulk crystal and placed on clear and flexible polydimethylsiloxane (PDMS) substrate using adhesive tapes, and then transferred onto quartz substrates for different studies. Figure 1c show the microscope image of a monolayer MoS 2 flake with ~100 μm length and ~50 μm width on 300 nm SiO 2 /Si substrate. 76 nm CH 3 NH 3 PbI 0 Height Sensor 20 mm -35 nm nm % (2) MAPI x (mm) Figure S2. AFM images of CH 3 NH 3 PbI 3. The CH 3 NH 3 PbI 3 films are ~30 nm thick. S3. System Response Deconvolution 4

5 To study the exact value of PB rising time in the CH 3 NH 3 PbI 3 -only films and vacancyengineered MoS 2 /CH 3 NH 3 PbI 3 heterostructures, the deconvolution of system response function must be performed. The simple convolution relationship can be expressed as: 3 f (s, t) f (s, t) g(s, t) 0 1 where s 0 is the PB rising value obtained from exponential decay fitting and f(s 1, t) is the instantaneous kinetics function, s 1 is the intrinsic PB rising time. g(s,t) is system response time. S4. Charge Transfer Modeling In order to investigate the charge transfer and relaxation process in the vacancy-engineered MoS 2 /perovskite heterostructure, we illustrate the related electronic states and processes (Figure S4) a b Pump Probe Pump Probe t Relax1 N M t CT t Relax2 N M CH 3 NH 3 PbI 3 Vacancy-engineered MoS 2 /CH 3 NH 3 PbI 3 5

6 Figure S4. (a) CH 3 NH 3 PbI 3 only films. (b) Vacancy-engineered MoS 2 /CH 3 NH 3 PbI 3 heterostructures In the initial photo excitation, the holes were generated at the hot hole states (state M in diagram). As the pump energy is larger than perovskite intrinsic bandgap (1.63 ev), state M is deeper than the valence band maximum VBM (State N in diagram). In the following relaxation processes, CH 3 NH 3 PbI 3 -only films and vacancy-engineered MoS 2 /CH 3 NH 3 PbI 3 heterostructures behave differently due to the structure surface and band alignment. (a) Hot hole cooling (t relax1 ) from State M to State N occurs in the CH 3 NH 3 PbI 3- only films (b) Besides hole cooling, an additional channel provides hole transfer process from State M of CH 3 NH 3 PbI 3 to vacancy-engineered MoS 2 in the hybrid heterostructures (a) CH 3 NH 3 PbI 3 -only films dn k M relax1 dt dm dt k relax1 M M M exp k t 0 relax1 (b) Vacancy-engineered MoS 2 /CH 3 NH 3 PbI 3 heterostructures dn k M relax2 dt 6

7 dm dt k M k M relax 2 CT M M exp( k t k t) 0 relax2 CT Here M, N refer to the hole density in state M and N, respectively. k relax1 is the hot hole cooling rate in CH 3 NH 3 PbI 3 - only films; k relax2 is the hole cooling rate in vacancy-engineered MoS 2 /CH 3 NH 3 PbI 3 heterostructures; k CT stands for the charge transfer rate from state M to vacancy-engineered MoS 2. M 0 is the entire hole density generated in state M initially after photoexcitation. Since the pump fluence we applied on CH 3 NH 3 PbI 3 -only films and vacancyengineered MoS 2 /CH 3 NH 3 PbI 3 heterostructures are the same, M 0 is constant in both situations. Herein, we could extract the simple equation: k k k relax1 relax2 CT As the decay rate is reciprocal to exponential time constant k 1, t t t t relax1 relax2 CT 7

8 S5. Triangular vacancy clusters and defect agglomerations 1.0 nm Figure S5. HR-TEM images showing triangular vacancy clusters highlighted by red arrows and defect agglomerations in the dashed line area. S6. Calculation Method In all calculations, the cut-off energy for the plane wave expansion of the wave functions is 500 ev, and the Hellman-Feynman forces are less than 10 mev/å. The semicores of Mo atoms are treated as valence electrons, that is 12 valence electrons for Mo (4p 6 4d 5 5s 1 ). 4 In the lattice parameters optimization of MoS 2 primitive cell, the Gamma centered Monkhorst-Pack grid of k-points for Brillouin zone integration was used. The optimized lattice parameters are a=b=3.18 Å, and c=13.99 Å. In the oxygen doping calculations, we constructed a monolayer supercell including 17 Å thick vacuum. One model is based on the substitution of 8

9 sulfur atoms by oxygen atoms; another model is based on the adsorption of O atom on the S site. A Monkhorst-pack grid is taken for Brillouin zone in doping electronic structure calculations. H f (α, 0) (ev) μ S = 0.0 ev (S-rich) μ Mo = 0.0 ev (S-poor) v S v Mo S Mo Mo S Table S1. The calculated defect formation energy H f (α, 0) of intrinsic defects and Oxygen defects in monolayer MoS 2. 9

10 Figure S6. The band offset of O-doped monolayer MoS 2 with different oxygen concentration. The Fermi level is referenced to the valence band maximum of the pristine monolayer MoS 2. The vacuum energy level is taken as the reference level for band alignment. S7. Topography images of MoS 2 monolayer before and after O 2 plasma We checked the topography of vacancy-engineered MoS 2 monolayer by Atomic Force Microscopy (AFM). By comparing with corresponding pristine MoS 2 monolayer that has not been treated with O 2 plasma, it is found that the topography are almost indistinguishable, which indicating that the mild O 2 plasma conditions we applied have little effect on the topography. The bright area is due to the wrinkle formed during transfer from flexible PDMS to Au substrate. a b 5.00 nm 0.00 nm Figure S7. (a) The AFM images of pristine MoS 2 monolayer. (b) the corresponding vacancyengineered MoS 2 monolayer (VM 4 in Figure 3). The scale bar is all 2 μm. 10

11 Energy (ev) S8. Ultrafast hole transfer between vacancy-engineered MoS 2 monolayer and CH 3 NH 3 PbI 3 upon excitation at 2.48 ev MoS MoS 2 2 CH 3 NH 3 PbI 3 Vacancy Engineered - Pump Pump WF: 4.4 WF: 4.7 WF t CT - t Relax Probe WF: Work Function Figure S8. A schematic of the hole transfer from CH 3 NH 3 PbI 3 to vacancy-engineered MoS 2 in the heterostructure with 2.48 ev excitation. S9. Experimental parameters of mild O 2 plasma treatment on MoS 2 monolayer. Samples VM 1 VM 2 VM 3 VM 4 VM 5 (Figure 5b) Power (w) Time (s) O 2 (sccm)

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