Research On Quantum Efficiency Optimization Of PbS Quantum Dots Photodetector

Lead sulfide（PbS）colloidal quantum dots are an inorganic semiconductor nanocrystalline material that can be prepared by low-cost solution method,with a continuously tunable band gap in the range of 0.5e V～1.9e V and obvious quantum-limited effect.In addition,it also has the advantages of good stability,high absorption coefficient in the near-infrared band and the ability to produce multi-exciton effects,which is considered as a promising material for short-wave infrared detection.However,the photodetector devices based on PbS colloidal quantum dots still have a certain gap with commercial photodetectors in terms of quantum efficiency as well as noise,which is due to the fact that during the preparation process,the thin films composing the devices produce various defects that affect the transport of photogenerated carriers within the devices.Therefore,this thesis focuses on the defects in the light absorption and electron transport layers in photovoltaic-type quantum dot photodetectors,and achieves the optimization of the external quantum efficiency of PbS quantum dot photodetectors by improving the surface morphology of each layer,the internal defects,and the interfacial contact between the layers.The details of the study are as follows:Firstly,PbS colloidal quantum dots with the first exciton absorption peak around 1600 nm were synthesized at 170°C using the thermal injection method,and the dispersion and size of PbS quantum dots were characterized by transmission electron microscopy（TEM）.The results show that the quantum dots used in the experiments are uniformly distributed with an average of about 7 nm,which provides a good foundation for the preparation of subsequent PbS quantum dot films and PbS quantum dot photodetectors.Secondly,by regulating the concentration of PbS quantum dot dispersant,ligand exchanger,the problems of many cracks and holes and roughness on the surface of PbS quantum dot films were improved.PbS quantum dot photodetectors were prepared using PbS quantum dot films treated with ligand exchanger concentration of 0.2%vol（before optimization）and PbS quantum dot films treated with ligand exchanger concentration of 1.0%vol（after optimization）,respectively,and the EQE of the devices was increase from 6%to 27%around 400 nm and from 1.2%to 4.5%.The EQE of the optimized device at 1600 nm increased by 3.8 times compared with the previous one.Finally,the defects in the ZnO films were optimized by adjusting the concentration of the ZnO precursor solution.As the concentration of the ZnO precursor solution increased,the percentage of defective oxygen in the ZnO films gradually decreased,and combined with the recrystallization caused by subsequent annealing,the film grains kept increasing,the absorption caused by the band-tailed states gradually decreased,the film crystallization process was more adequate,and the defective states in the films gradually decreased.However,due to the increase of solute,the roughness of the film surface gradually increases,and under the combined influence of both factors,the photodetector devices prepared with the participation of ZnO films prepared using the solution with the concentration of 0.7M（mol/L）are able to obtain the most excellent performance,and the responsiveness and specific detectivity of the devices are enhanced to 0.32 A/W and 3.48×10¹¹Jones level with an EQE of 25%,and the response time of the device isτ_R=130μs andτ_F=20μs.