Design,Construction And Optoelectronic Performance Investigation On The Perovskite Based Mixed-Dimensional Van Der Waals Heterostructure Photodetector

Heterostructures are extremely important as a fundamental structure in various semiconductor devices.With the rapid development of two-dimensional(2D)materials and heterostructures.0D-2D mixed-dimensional van der Waals heterostructures(MvdWHs)emerged.,combining remarkable optical properties of various OD quantum dots(QDs)and intriguing physical properties of 2D layered materials.Overcoming the strong interlayer coupling,weak total optical absorption.limited modulation of interfacial charge behavior and etc.in stacked 2D/2D vd WHs,0D-2D MvdWHs have attracted tremendous attention.Devices based on OD QDs-2D TMDs MvdWHs have been demonstrated to be an ideal platform for ultrasensitive and broadband detection with high efficiency and photogain effect.In spite of their promising prospects.some problems remained in term of this novel MvdWHs and their optoelectronic devices.For one thing,considering the contact difference of the two neighboring crystal,i.e.from entire face-face contact to point-face contact,the interface of MvdWHs is more complex compared with conventional heterostructures.Hence,both interfacial concepts and modulation protocols need to be reconsidered for MvdWHs.For another,the potential working mechanism responsible for ultrasensitive photodetection based on this novel MvdWHs is not well understood.Furthermore,the negative effects on the interfacial charge transfer efficiency originated from the residue ligands that inevitably introduced by the QDs is still prominently remained.From these perspectives,in answer to the proposed question,we first taking energy band engineering as a typical example to systematically investigate its effectiveness in 0D-2D MvdWHs system for the first time.Taking advantage of tunable bandgap for perovskite QDs,we realized a series band alignment of perovskite QDs/MoS2 monolayer 0D-2D MvdWHs via tuning the electronic structure of the perovskite crystal.The interfacial charge behavior were clearly verified to be influenced by varied band alignment in 0D-2D MvdWHs via sufficient comparison of a series optical characterization results,the corresponding phototransistors'performance based on precisely designed type ? and type ? band alignment and the photocurrent generation mechanism.Benefiting from the intrinsic superiority of perovskite materials,all-inorganic cesium lead halides perovskite quantum dots were integrated with monolayer MoS2 to realize an ultrasensitive 0D-2D mixed-dimensional photodetector.Owing to the synergistic effect of photogating mechanism and Schottky barriers modulation,the phototransistor exhibited an ultrahigh photoresponsivity of 7.7×104 A/W,a specific detectivity of?5.6×1011 Jones,and an external quantum efficiency exceeding 107%.Due to the low-temperature solution-processability and wide range bandgap-tunability of perovskite QDs.,such 0D-2D mixed-dimensional system would open up a wide realm of opportunities for designing low-cost,flexible and high-performance optoelectronics.To address the negative effects caused by surface capping ligands,we demonstrated a ligand engineering to balance the QDs surface passivation and the interfacial charge carrier transfer efficiency inside 0D-2D MvdWH interface for the first time.The accurately adjustment of ligand density outside QDs enabled the subsequent improved interfacial charge carrier transfer efficiency from aspect of electronic and optoelectronic properties.Furthermore,such kind of ligand engineering towards MvdWH based phototransistor with an order of magnitude higher photoresponsivity of 1.13 × 105A W-1.These results may push forward the evolution of 0D-2D mixed-dimensional van der Waals optoelectronics.In this thesis,towards design and construction of high performance 0D-2D mixed-dimensional van der Waals optoelectronic devices,from the energy band engineering,interface engineering and ligand engineering etc.perspectives,clarified the effectiveness of traditional energy band engineering inside 0D-2D MvdWH interface,realized an ultrasensitive 0D-2D mixed-dimensional photodetector and elaborated the underlying mechanism,proposed a new strategy to improve carrier transfer efficiency in 0D-2D mixed-dimensional system and further optimized the optoelectronic performance of the device,which may give impetus to effectively promote the 0D-2D mixed-dimensional van der Waals optoelectronics evolution.