Towards Hyperspectral Imaging:Study On Perovskite/PbS Quantum Dot Heterostructured Photodetectors

In recent years,hyperspectral imaging technology has attracted immerse attention in various fields including remote sensing detection,medical diagnosis and food and chem-ical monitoring due to its powerful capability to obtain target information.As one of the core elements of hyperspectral imaging system,a broadband photodetector that can re-spond to the wide ultraviolet-visible-near infrared(UV-vis-NIR)spectrum is of great re-search significance,considered as the research hotspot in the field of photoelectric detec-tion.As a new type of photosensitive material,organic-inorganic hybrid perovskites rep-resented by methylamino lead halide(CH3NH3PbX3)show significant advantages over traditional semiconductors and organic materials in the field of optoelectronics,and are expected to realize high-performance broadband photodetectors.However,the relatively large bandgap value limits its spectrum detection range,which further inhibits its appli-cations in broadband photodetectors.Aiming at the broadband photodetection applica-tions,the CH3NH3PbI3/PbS colloidal quantum dot(CQD)heterojunction was proposed and implemented.This heterojunction can both broaden absorption spectrum to infrared region and improve the photo-generated carrier separation,resulting in high-responsivity broadband photodetectors.Based on the CH3NH3PbI3/PbS CQD heterojunction,the lat-eral photoconductor-type and vertical photodiode-type broadband photodetectors have been implemented.Systematic optimizations of devices were carried out to explore suit-able device design for large-scale array integration,and their potential applications in hyperspectral imaging were further verified.(1)The perovskite/PbS CQD heterojunction integrated broadband photoconductor was firstly realized.Interfacial photocarriers generation,separation and transport mecha-nisms were explored,and then key aspects affecting the photodetection behaviors were obtained.Through optimization design of surface ligands of PbS CQDs,the SCN-anion was found to significantly improve the photoresponsivity of lateral CH3NH3PbI3/PbS CQD heterostructured photodetectors.The CH3NH3PbI3/PbS-SCN heterostructured pho-todetectors are sensitive to a broad wavelength range covering the UV-vis-NIR region(365-1550 nm),possessing an excellent responsivity of 255 AW-1 at 365 nm and 1.6 AW1-at 940 nm,remarkable high detectivity of 4.9×1013Jones at 365 nm and 3.0×1011 Jones at 940 nm.Furthermore,based on the lateral photoconductor,a 10×10 broadband imaging array is constructed,which can realize imaging display in the range of UV-vis-NIR.(2)In order to further improve the device quality factor such as response speed and operation voltage,CH3NH3PbI3/PbS CQD heterostructured photodiodes were construc-tured with a structure of "ITO/ZnO/PbS-EDT/CH3NH3PbI3/Spiro-OMeTAD/MoO3/Ag".The mechanisms of photocarriers generation,separation and transport were investigated in detail,and then key parameters with respect to the photodetection behaviors were ob-tained.Through optimization of PbS CQD layer number,perovskite film fabrication pro-cess and functional layers,broadband photodiodes with fast response speed(ton=14 ?s,toff=35 ?s)and low work voltage(even can work under zero bias voltage)were achieved.Under a-0.5 V work voltage,this device possesses a high responsivity of 416 mAW-1 at 365 nm and 39 mAW-1 at 940 nm,remarkable high detectivity of 1.44×1012 Jones at 365 nm and 1.36 × 1011 Jones at 940 nm.(3)Based on perovskite/PbS QDs heterostructured photodiode linear array,the over-all framework of board-level line scanning imaging system was designed.The resistor feedback amplifier circuit based on high precision resistive trans-impedance amplifier,16-bit sampling quantization precision circuit and microprocessor control circuit were designed and implemented to achieve the line scanning system circuits.A line array im-aging system based on perovskite/PbS QDs heterojunction photodiode was realized.The CH3NH3PbI3/PbS CQD heterostructured photodetectors that can realize UV-vis-NIR broadband photodetecton were proposed and implemented,the internal mechanism and realization method of the high performance broadband photodetection were obtained,providing a feasible way for future implementation of high-performance and low-cost broadband imaging chip in hyperspectral imaging system.At the same time,the line array scanning imaging system designed to match the device can provide a general technical scheme reference for the imaging applications of novel photodetectors based on organic and QDs sensitive materials.