| Flexible optoelectronic devices are set to play a crucial role in future smart and wearable technologies.Low-dimensional materials,which possess exceptional properties such as quantum confinement effect,flexibility,and high surface atomic ratio,have captured significant attention in the field of flexible optoelectronics.These properties set them apart from bulk materials,making them ideal for such applications.To achieve high-performance flexible optoelectronics,it is crucial to develop suitable low-dimensional materials.Recently,monoelemental two-dimensional(2D)materials,named Xenes,have emerged as a rising star in this field.Xenes have a unique crystal structure that provides them with ultra-high mobility and an adjustable band gap,allowing them to detect light across a wide range of the electromagnetic spectrum,from ultraviolet to near-infrared spectral regions.These properties make Xenes the most promising 2D materials for photodetectors.Additionally,one-dimensional carbon nanotubes(CNTs)exhibit diameter-dependent band gaps,making them highly suitable for flexible optoelectronics.However,the successful application of these materials depends on large-scale preparation.Unlike traditional 2D materials such as graphene,Xenes have narrower interlayer spacing and stronger binding energy,which makes their large-scale exfoliation challenging.Similarly,controlling the high coverage and diameters of CNTs seems impossible.This dissertation addresses these challenges by developing new methods such as polymer ionic liquids(PILs)assisted liquid phase exfoliation and cathode intercalation exfoliation methods to efficiently prepare 2D Xenes.Moreover,the dissertation demonstrates that CNTs with narrow diameter distribution and full coverage can be grown in situ on the inner wall of optical fibers,forming CNT-PCFs.The optical,nonlinear optical,and electrical properties of these materials are investigated,and flexible devices are prepared.The responsivity and specific detectivity of Xenes-based flexible photodetectors are improved by modifying PILs or constructing heterojunctions.Finally,the dissertation demonstrates the successful fabrication of fiber lasers based on CNT-PCFs.Overall,this dissertation provides new strategies for the large-scale preparation of low-dimensional materials,paving the way for their use in flexible photodetectors,and even smart and wearable devices.The main contents are listed below:Chapter one: Reviewing the basic parameters and special requirements of flexible devices and discussing the reason for choosing Xenes and SWNTs.The structure details and properties of Xenes and SWNTs are elaborated,along with the preparation method of Xenes.Additionally,the progress of Xenes based photodetectors is summarized and classified by photodetection mechanisms,leading to the motivation for the dissertation.Chapter two: A novel cathode intercalation exfoliation method was developed to efficiently prepare tellurium nanostructures with different dimensions,which showed dimensional dependent nonlinear optical properties.It is demonstrated that zero-dimensional(0D)Te nanoparticles exhibit superior optical nonlinearity to graphene.Moreover,one-dimensional(1D)Te nanowires and quasi-1D Te nanorods exhibit even higher saturable absorption than 0D Te,indicating promising applications in ultrafast laser.The chapter concludes by showing that 2D Te is a high-performance optical limiting material,broadening its applications to laser protection and related fields.Chapter three: Fabricating self-powered flexible photodetectors based on tellurium nanostructures.It is shown that flexible photodetectors based on Te NRs have an excellent responsivity of 6.1 A W-1,and the detectivity achieves 1.2 × 1011 Jones,which is the highest among Te-based photodetectors.Self-powered photodetectors based on Te NRs/Te NDs are also successfully fabricated,which exhibits a responsivity of 3 μA W-1.Due to the absence of bias voltage,the dark current is nearly zero,showing ultra-sensitive responses to weak light.This chapter paves the way for the applications of Te nanomaterials in self-powered flexible optoelectronics.Chapter four: Antimonene based flexible photodetectors were fabricated.PILs assisted liquid-phase exfoliation method is developed to prepare few-layered antimonene with the highest yield above 20%.The energy band of antimonene is modified by oxidation introduced during exfoliation,and as-prepared antimonene nanosheets are further hybridized with Cd S quantum dots to improve the light absorbance of the composite material.For the first time,flexible photodetectors based on antimonene are successfully fabricated,which show a good responsivity of 10 μA W-1 and on/off ratio of 26.8.This chapter demonstrates an efficient method to prepare antimonene and enables the applications of antimonene in optoelectronics.Chapter five: Utilizing the topological insulating properties of 2D bismuth by exfoliation method for ultra-sensitive acoustic detection.large-scale Bi(110)nanosheets are successfully fabricated by a novel electrochemical intercalation method,using Intercalators with suitable radius to the interlayer spacing of Bi(110)such as K+.For the first time,acoustic detector is demonstrated based on 2D Bi porous films,which can even detect the sound of 45 d B.The flexible sensors were used for acoustic-toelectric energy conversion,information transfer such as “LZU” and “SOS”,and even as a “danger” detector in a “hide-and-seek” game.This chapter provides a promising approach for scalable fabrication of ultrathin Bi(110)nanosheets and paves the way for its application in acoustic detection and smart devices.Chapter six: Optical fibres embedded with as-grown CNTs for ultrahigh nonlinear optical responses.We report the direct growth of CNTs on the inner wall of a PCF by chemical vapor deposition method,fabricating a new functional fibre,CNTPCF.A two-step growth method was developed to control the full-coverage and narrow diameter distribution of CNTs to ensure desirable optical transitions.In the asfabricated 3-cm-long fibre,third-harmonic generation has been enhanced by ~15 times compared with flat CNT film on fused silica.We further demonstrated a dualwavelength all-fibre mode-locked ultrafast laser(1550 nm and 1064 nm)by integrating the 1.36±0.15 nm-diameter CNTs into two kinds of photonic bandgap PCF(HC-1550 and HC-1064)as saturable absorbers,using its S11(~ 0.7 e V)and S22(~ 1.2 e V)interband transition respectively.The fibre laser shows stable output of ~10 m W,~800fs pulse width and ~71.4 MHz repetition rate in the 1550 nm wavelength.Our results can enable the large-scale applications of CNTs in the PCF-based optical devices. |
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