| Semiconductor quantum dots (QDs) with size-tunable emission properties have been widely applied inlight-emitting devices (LEDs), photovoltaic cells, and biological labels. After two decades of research anddevelopment, many high quality QDs have been synthesized successfully. Lead sulfide (PbS) is a veryimportant semiconductor material, whose bandgap is about0.41eV at room temperature, and therefore hasa good light absorption in the visible range. In recent years, with the development of nanotechnologyresearches, PbS nanoparticles have been researched extensively due to its excellent optical and electricalproperties. In addition, QD-based light emitting devices (QD-LEDs) possess the potential to be the nextgeneration solid state lighting source for display and illumination due to the size-tunable emission, narrowemission full width at half maximum (FWHM), high PL QY and thermal stability of QDs. The core-shellstructured CdSe/ZnS quantum dots, due to its high stability and quantum yield, have been widely used asthe light-emitting material for QD-LEDs. However, only a few reports in the field of light-emitting devicesdealt with water-soluble CdSe/ZnS quantum dots. In this thesis, the voltage-current characteristics of thePbS quantum dot solar cells, as well as the electro-optical properties of quantum dot-based light emittingdevices which using water-soluble CdSe/ZnS QDs were studied in detail. And the thesis contains thefollowing two parts:(1) Water-soluble CdSe/ZnS quantum dot light emitting devices: In this part, the relationship betweenthe thickness of light-emitting layer, which is fabricated with a spin-coating method, and the emissionbehavior of devices were first examined. And a configuration with3-bilayer structure was found to be theoptimal thickness for emission layer with peak luminances of about400cd/m2. Stability testing indicatesthat a severe attenuation of brightness occurred within only a few hours. Then, other factors that mightinfluence the performance devices were also analyzed, such as the introduction of inorganic ZnOnanocrystal as electron transport material, the adoption of Poly-TPD as hole transport material, and the wayused for annealing processes, but no obvious improvement could be obtained. As an effective way toprecisely control the film thickness, the layer-by-layer assembly method were introduced to fabricateQD-LEDs utilizing water soluble CdSe/ZnS QDs. By comparing the performances of devices with QD/PDDA bilayers varying from1to10, the relationship between the thickness of light-emitting materialand the electoluminescent behavior were discussed in detail. Devices with8QD/PDDA bilayersdemonstrate the highest brightness of about1000cd/m2. Stability test was also carried out, and nosignificant attenuation was observed within two weeks. ZnO, Poly-TPD, different heat treatment processes,and other factors that might impact the emission behavior of QD-LEDs, are also analyzed with a optimaldevice structure of8QD/PDDA bilayers. Through the comparison of performance of devices fabricatedusing spin-coating and layer-by-layer assembly, it seems that the layer-by-layer assembly method is moresuitable for the fabrication of high performance QD-LEDs with water-soluble QDs as emission medium.(2) PbS quantum dot solar cell: the influence of QD morphology, such as dot-, cube-and flower-likeshapes on the voltage-current characteristic was extensively investigated. Taking the cubic PbS as anexample, other factors such as concentration, particle size, and heat treatment processes were alsoinvestigated. And the results indicated that the devices fabricated under inert ambient and annealed at200℃demonstrated the best electrical properties. Subsequently, light response and conversion efficiencywere tested, and the influencing factors of cell performance were discussed. |
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