Preparation Of Monolayer WS₂/CsSnBr₃ Heterostructure And Their Exciton Dynamics And Photoresponse

Two-dimensional transition metal dichalcogenides(TMDCs)have been widely studied due to their unique structure and optoelectronic properties.Monolayer WS2,in particular,has the advantage of high mobility for the application in optoelectronic devices.However,the application of monolayer WS2 typically depends on growth techniques and transfer processes,and the material itself has poor capability of light absorbance,making it difficult to fully utilize its excellent optoelectronic properties.In this study,large-area monolayer WS2 was obtained directly on Si/SiO2 substrate by chemical vapor deposition(CVD),and a heterojunction was formed by vacuum deposition of CsSnBr3 perovskite on it.The influence of CsSnBr3 thickness on the surface morphology,structure,and photoluminescence(PL)of the heterojunction was investigated.The results show that at lower thicknesses,CsSnBr3 grows selectively on WS2 nanosheets,and the WS2 nanosheets significantly enhance the crystallization of the perovskite.It was also found that there was strong PL quenching of both materials in the heterojunction,indicating strong interlayer coupling between WS2 and CsSnBr3 at the interface.UV-visible absorption spectroscopy and X-ray photoelectron spectroscopy(XPS)results confirmed the formation of a Type Ⅱ heterojunction at the interface,which is capable to separate photo-generated charge carriers and transfer a large number of holes from the CsSnBr3 perovskite to WS2,resulting in PL quenching.Subsequently,it was demonstrated by time-resolved photoluminescence spectroscopy(TRPL)that the increased exciton lifetime at the wavelength of 638nm in the heterojunction was due to the transfer of a large number of holes from the CsSnBr3 perovskite to WS2,and there was no energy transfer between CsSnBr3 and WS2.Finally,it was found that the photodetector fabricated by depositing a 50nm-thick CsSnBr3 layer to form a heterojunction with the beneath monolayer WS2,greatly separated photo-generated charge carriers,transported a large number of holes,and significantly increased the field-effect hole mobility of the WS2/CsSnBr3 photodetector.At the optimal response wavelength of 330nm,the field-effect hole mobility increased from 1040.15 at dark condition to 1675.08 cm2V-1S-1 at illumination,and a photocurrent of 1.6A/W was achieved at a bias voltage of 5V,which was 50 and 20 times higher than those of the isolated 50nm CsSnBr3 and monolayer WS2 devices,respectively.The study not only demonstrated that the built-in electric field of the WS2/CsSnBr3 heterojunction is capable to greatly promote the separation of photo-generated charge carriers,but also prove that tin-based perovskite can be used as a light-absorbing and charge carrier transporting layer to construct a photodetector with WS2.