Field Effect Transistors Based on Van-der-Waals. Grown and Dry Transferred All-Inorganic

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1 Supporting Information for Field Effect Transistors Based on Van-der-Waals Grown and Dry Transferred All-Inorganic Perovskites Ultrathin Platelets Chengxue Huo #, Xuhai Liu #, Xiufeng Song, Ziming Wang, and Haibo Zeng* MIIT Key Laboratory of Advanced Display Materials and Devices Institute of Optoelectronics & Nanomaterials, College of Material Science and Engineering, Nanjing University of Science and Technology, Nanjing , China # These authors contribute equally to this work. *Authors to whom correspondence should be addressed, zeng.haibo@njust.edu.cn S1

2 Methods Fabrication of CsPbBr 3 ultrathin platelets and characterization: CsPbBr 3 ultrathin platelets were prepared by van-der-waals epitaxy. The substrate mica was sliced into several ultrathin pieces along its c-axis, and subsequently placed inside the downstream of quartz tube in a single zone furnace. The source was mixed powder of PbBr 2 and CsBr with molar ratio 1:1. The quartz tube was pumped down to 10 Pa after the substrates and source were placed inside. Afterwards, high purity Ar (99.99%) was passing through the tube until the atmospheric pressure was achieved. This was followed by a 35 sccm flow of high purity Ar and the reaction was carried out under atmospheric pressure. Within 20 min., the reaction temperature was increased from room temperature to 575 C and then hold for 15 min. XRD patterns were recorded on a Bruker D8 multipurpose system. UV/Vis absorption spectra were obtained on a Shimadzu 3600 spectrophotometer. PL spectra were obtained with the excitation wavelength of 365 nm by Aramis from HORIBA JOBIN YVON. Optical images were captured by Olympus BX51. SEM and AFM images were taken by FEI Quanta 250FEG and a Bruker Multimode 8 AFM system, respectively. In-situ XRD was carried out by Smartlab 9 kw of RIGAKU. Transfer of ultrathin platelets and characterization of of FETs: PVA aqueous solution with 8 wt% was dropped on a CD disk to form a thin film and heated at 70 C. Afterwards, a piece of the PVA film was placed on perovskite ultrathin platelets grown on mica. The PVA film bonded the ultrathin platelets after being heated for 5 minutes at 80 C. Then, the PVA film with ultrathin platelets were transferred onto prepatterned Au electrodes on the SiO 2 /Si substrate under microscope. The channel length is 20 µm and channel width ranging from µm. The output and transfer characteristics together with the temporal electrical responses were measured S2

3 by a Keysight B1500A semiconductor analyser. The low temperature electrical measurements were carried out using a Helium Cryogenic Equipment System with a Model 32 temperature controller. Figure S1. Schematic diagram of preparation of CsPbX 3 ultrathin platelets. S3

4 Figure S2. Optical images of (a) CsPbCl 3, (b) CsPbBr 3, and (c) CsPbI 3. S4

5 Figure S3. Optical images of CsPbBr3 ultrathin platelets on different substrates (a) SiO2/Si, (b) GaN, (c) FTO glass, (d) graphene. Figure S4. (a) Optical image of a CsPbBr3 nanoplatelet, the lateral size is about 320 µm. (b) Corresponding AFM image, the thickness of this ultrathin platelet is about 300 nm. S5

6 Figure S5. SEM image of CsPbBr 3 ultrathin platelets, exhibiting no grain boundary in the platelet. Figure S6. AFM image of CsPbBr 3, the surface roughness of the ultrathin platelets is 0.43 nm. S6

Dark field optical image of FETs corresponding to Figure 2b.

7 Figure S7. (a) SEM-EDS spectrum of CsPbBr 3 ultrathin platelets. (b) EDS-Mapping of CsPbBr 3 ultrathin platelets. Figure S8. Dark field optical image of FETs corresponding to Figure 2b. The bright green can be observed by naked eyes from the samples under the microscope, which suggests the excellent crystal quality of platelets. S7

8 Figure S9. Transfer characteristics of CsPbBr 3 FET under forward and back bias voltage at room temperature. Figure S10. Fitting results for calculation mobility at room temperature (a) and 237 K (b). S8

Figure S11. Histograms (obtained from 20 samples) of mobilites at room temperature (a), and 237 K (b). Figure S12. FET characteristics of CsPbBr3 thin film transistor.

9 Figure S11. Histograms (obtained from 20 samples) of mobilites at room temperature (a), and 237 K (b). Figure S12. FET characteristics of CsPbBr3 thin film transistor. (a) SEM image of CsPbBr3 thin film. (b) Output characteristics of the thin film transistor at room temperature. (c) Transfer characteristics of the thin film transistor at room temperature. (d) Transfer characteristics of the thin film transistor at 237 K. S9

10 Figure S13. Temperature dependence of the transistor mobility of five different devices. Figure S14. (a) In-situ XRD spectra of CsPbBr3 ultrathin platelets grown on mica at different temperature from 297 K to 77 K. (b) Partial enlarged details of (a). S10

11 Figure S15. Stability investigation of the transfer characteristics of a CsPbBr 3 ultrathin platelet transistor. S11

12 Table S1. Comparison of the room temperature FET performance of this work with previous work in literature. Material Material structure µ e (cm 2 V - 1 s -1 ) µ h (cm 2 V - 1 s -1 ) On-Off ratio Ref. PEASnI 4 Thin film [9] PEASnI 4 Thin film [10] PEASnI 4 Thin film [11] MAPbI 3 Thin film [12] MAPbI 3 Thin film [13] MAPbI 3 Thin film [14] Cs x (MA 0.17 FA 0.83 ) 1-x Pb(Br 0.17 I 0.83 ) 3 Thin film [15] CsPbBr 3 Ultrathin platelets Our work S12

350 C for 8 hours in argon atmosphere. Supplementary Figures. Supplementary Figure 1 High-temperature annealing of BP flakes on SiO 2.

350 C for 8 hours in argon atmosphere. Supplementary Figures. Supplementary Figure 1 High-temperature annealing of BP flakes on SiO 2. Supplementary Figures Supplementary Figure 1 High-temperature annealing of BP flakes on SiO 2. (a-d) The optical images of three BP flakes on a SiO 2 substrate before (a,b) and after annealing (c,d) at