Lead Sulfide Quantum Dots Based Optoelectronic Materials And Devices

Quantum dots(QDs)are semiconductor nanocrystals in the diameter of 2~10 nm with quantum size effect.QDs are widely utilized in photovoltaic device,photodetector,light emitting diode,etc.During the development of QD-based solar cell,the optimization of QD synthesis process,improvement of surface passivation and device structure design have greatly promoted the performance of the device.Meanwhile,the combination of QDs with 2D,3D or bulk materials not only combines the advantages of these materials,but also produces new material properties.The main contents of this dissertation include three aspects: inverted structural lead sulfide(Pb S)QD solar cell,QD-in-perovskite nanowire composites and preparation of narrow bandgap QD-in-perovskite nanocomposite.The second chapter demonstrates the inverted structural Pb S QD solar cell.The highest efficiency of inverted structural Pb S QD solar cell was obtained through device structure design,optimization of fabrication process,device model simulation and analysis of experimental results.During the optimization of device fabrication process,power conversion efficiency is the main parameter to determine the proper preparation conditions.It is revealed that both device preparation process and device testing process need to be carried out in the air and the relative air humidity should be ~50%.Then sol-gel nickel oxide(Ni Ox),Pb S QDs capped with iodide and zinc oxide were selected as hole transporting layer,absorbing layer and electron transporting layer respectively.The performance of the best device are as open circuit voltage of 0.519 V,short circuit current density of 27.08 m A/cm~2,filling factor of 60.9%,and power conversion efficiency of 8.56%.Through the insertion of a buffer layer between Ni Ox and Pb S QDs,the interface recombination are effectively suppressed,resulting in the performance of the device as open circuit voltage of 0.532 V,short circuit current density of 27.68 m A/cm~2,filling factor of 65.7%,and the power conversion efficiency of 9.7%.Furthermore,mechanism of the improved device performance is revealed through the characterization of physical parameters and the device model simulation results.It is proved that the depletion region between Ni Ox and Pb S QDs promotes the carriers extraction.And the introduction of a buffer layer inhibits the interface recombination,leading to an improvement of open circuit voltage.The third chapter describes the design and fabrication of QD-in-perovskite nanowire composites.The photoconductive detector and solar cell with infrared response were made after optimizing the material preparation process and exploration of their application in photoelectric device.The influence of QD fraction,solvent concentration and growth time on nanowire growth was explored.And the structure information,material properties of the composites and proper fabrication process were obtained through analyzing the results of absorption spectra,fluorescence spectra,XRD,TEM and EDS.The photodetector was prepared with the composites prepared by scheme I.The performance of the device was demonstrated by current-voltage curve,time response curve,responsivity and near infrared response characteristic.The solar cell was fabricated with the composites prepared by scheme II.The nanowire solar cell used zinc oxide(Zn O)as electron transporting layer,QD-in-nanowire composites as light absorbing layer and spiro-Me OTAD as hole transporting layer,resulting in a dot-in-nanowire composites solar cell with near infrared photocurrent response characteristic.The fourth chapter is the preparation of narrow bandgap QD-in-perovskite nanocomposites.Firstly,the synthesis process of Pb S QDs was optimized and stable large-sized Pb S CQDs with exciton peaks in ~1300 nm and ~1500 nm was obtained.Secondly,the liquid phase ligand exchange process of large-sized QDs was explored to determine a suitable ligand exchange process.Thirdly,the Pb S QDs with exciton peak ~1300 nm were used in the preparation of QD-in-perovskite films.The fluorescence signal difference between different preparation conditions and the resonant fluorescence single photon source signal of the composite were explored.