Synthesis Of High-Quality Colloidal Quantum Dots For Efficient Photovoltaic Applications

Colloidal quantum dots have attracted tremendous attention in the community of optoelectronic devices,due to their unique properties.Despite the rapid development of QDs photovoltaic technology,there are still many problems to be solved.For instance,the low synthetic yield of lead sulfide quantum dots(PbS QDs)is one of the major bottlenecks that hampers the commercialization progress.And all previous efforts are only focused on QDs yield,while the quality of the nanocrystals from scale-up synthesis and their resultant device applications have rarely been investigated.As new emerging QDs developed rapidly in recent years,perovskite QDs have shown huge application potential in the field of photovoltaic devices and light-emitting diodes.But their poor device efficiency and stability still need to be improved.Solving the above problems will accelerate the development of emerging QDs PV technology.Hence in this work,starting from the synthesis of QDs,we increased the yield of PbS QDs by optimizing the reaction conditions without affecting the material properties.In addition,we introduced passivation agents to improve the stability of the perovskite QDs and the device performance.The specific research content can be divided into the following four parts:Chapter 1:The introduction of basic properties of quantum dots,the research progress of PbS and perovskite quantum dot solar cells.Chapter 2:Based on the classical hot injection method,we significantly improved the reaction yield of PbS QDs by increasing the precursor concentration.Moreover,we systematically studied the effect of the reaction concentration on the quality of the PbS QDs and the performance of solar cells.We demonstrated that increasing the precursor concentration to 15.8 M(200-fold)can effectively increase the yield,at the same time without significantly affecting the particle size,size distribution,optical properties,crystal structure and surface composition of PbS QDs.In addition,the solar cells based on these PbS QDs show excellent perfonnance with stable efficiency in the range from 10%to 10.5%.We also proved that the highly concentrated synthesis can be a general approach to apply to different lead precursors.Our approach can provide high-quality PbS QDs in large quantities,paving the way to the future large-scale manufacturing of QDs solar cells.Chapter 3:We used the conventional hot-injection method to synthesize CsPbI3 and FAPbI3 QDs.The optical properties and morphology of CsPbI3 and FAPbI3 QDs were systematically characterized by UV-vis absorption spectrum,fluorescence spectrum and transmission electron microscope.Futher,the solar cells based on CsPbI3 QDs and FAPbI3 QDs show excellent performance with efficiencies of 12.55%and 9.93%,respectively.Chapter 4:We synthesized lead-free CsSnI3 QDs by conventional hot-injection method.By optimizing the QDs purification method,we obtained high quality CsSnI3 perovskite QDs.Further,we modified the synthesis method to enhance the air stability of the prepared CsSnI3 QDs by introducing a surface passivation agent.Finally,we systematically studied the effects of different passivation methods on the performance of the CsSnI3 perovskite QDs solar cell.In summary,taking the classical PbS QDs as an example,we studied the effects of scale-up synthesis on the quality of QDs and their photovoltaic performance,which will benefit the application of QDs in optoelectronic devices in the future.At the same time,we have improved the properties of perovskite QDs and the performance of photovoltaic devices through the regulation of synthetic methods,and it can further promote the application of such materials in solar cells.