Research On Near Infrared Light Emitting Diodes Based On Lead Sulfide Quantum Dots

Near-infrared light-emitting diodes have been widely used.However,to meet the needs of future large-area,flexible,multi-spectral tuning and low-cost near-infrared light sources,new near-infrared luminescent materials and devices are required.Quantum dots are a new class of semiconductors can control the wavelength of light emission by regulating the particle size due to the quantum confinement effect.Besides,the cost is low because of its solution method synthesis.Lead sulfide quantum dots have become one of the ideal new near-infrared light-emitting diode materials thanks to their near-infrared luminescence,high quantum yield,uniform particle size distribution and stability in air.The main research content of this paper focus on near-infrared light-emitting diode based on lead sulfide quantum dots.The surface engineering of lead sulfide quantum dots,the film formation quality in the ligand exchange process and its influence on device performance were explored.The device physics based on ligand exchange process was studied to improve the carrier injection balance,enhance the probability of radiative recombination,and then improve device performance.The achievements were shown below:1.In terms of surface engineering,the lead sulfide quantum dots are surface-modified with short-chain organic ligand 3-mercaptopropionic acid?3 methylene groups?and 8-mercaptooctanoic acid?8 methylene groups?to improve mobility.But the problem of film cracking caused by long chain shortening chain followed,to solve this,we optimized the cleaning method to improve the quality of 3-mercaptopropionic acid ligand film;while the length of 8-mercaptooctanoic acid ligand is longer,the film crack disappears after improvement.A near-infrared light-emitting diode with an external quantum efficiency peak of 0.2%and a peak radiance of 3 W Sr^-1 m^-2 was obtained,the device structure was ITO/PEDOT:PSS/QDs/ZnO/Al.2.In terms of charge balance,the probability of radiative recombination and carrier injection balance is enhanced by improving hole transport and injection,and blocking the transmission of excess electrons.We chose CBP as hole transport layer,because of CBP with higher hole mobility(¹0^-3 cm² V^-1 S^-1)than PEDOT:PSS(2.64×10^-4 cm² V^-1 S^-1),which is much lower than electron mobility of ZnO(¹0^-3cm² V^-1 S^-1),and CBP can be used as the electron blocking layer effectively blocks the transmission of electrons to enhance the probability of radiative recombination due to the LUMO level of CBP is 2.8 eV.In addition,we chose MoO₃ as the buffer layer and the energy level adjustment layer thanks to the HOMO level of CBP?6 eV?is too bigger than the work function of Al?4.3 eV?,the energy level of MoO₃/Al reaches 5.8 eV.The external quantum efficiency peak of the device is increased to0.3%,and the peak radiance is increased to 5.2 W Sr^-1 m^-2.3.The injection of holes is further improved by added a modification layer HAT-CN between the Al electrode and MoO₃.Because of the LUMO level of HAT-CN and MoO₃ are very deep,increasing the hole concentration of the CBP layer,significantly concentrate the electrons of the adjacent hole transport layer?CBP?,providing a larger hole current,further improving the load.The flow is injected into the balance.The external quantum efficiency of the device is increased to 0.8%,and the peak radiance is increased to 5.5 W Sr^-1 m^-2.In this thesis,the surface engineering of lead sulfide quantum dots is studied.The optimization of quantum dot film quality is improved,the carrier injection balance is improved,and the external quantum efficiency and radiance of quantum dot near-infrared light-emitting diodes are effectively improved.