The Synthesis Of Semiconductor Nanocrystals And Their Application In Optoelectronic Devices

Colloidal semiconductor nanocrystals?abbreviated as NCs?are solution-processed inorganic functional materials.As-synthesized NCs are usually capped with surfactants,which endow them with good dispersity and capacity for large area processing.NCs possess many kinds of unique optoelectronic properties,showing great potential for application in biological imaging,light-emitting diodes?LED?,laser and solar cells.Although,the properties and application of NCs have been investigated for more than 20 years with a lot of achievements,we need to further understand the effects of NCs surface states,morphology and crystal structure et al.on their properties and device performance for realizing commercialization.In this dissertation,we investigated the effect of synthesis conditions on the basic properties of NCs and corresponding device performances for solar cells and pulse lasers,demonstrating the significant impact of NCs design and modification on device performance.The specific research results are listed as follows:Chapter 1: The basic properties of NCs.The progress of pure NCs solar cells and polymer/NCs hybrid solar cells,the basic properties and application of self-doped plasmonic semiconductor NCs are discussed.Chapter 2: The mechanism study of the decomposition and transformation of CsPbBr₃ NCs to uniform Cs₄PbBr₆ NCs.We found that CsPbBr₃ nanocubes can be decomposed to layer structured X²⁺[PbBr₄]₂-within tens of seconds,which then further growth to uniform Cs₄PbBr₆ rhombus within about 200 s.These processes can be performed under air condition at room temperature.The research of this decomposition process would help to understand the instability of CsPbBr₃ NCs and thus to improve the stability of this kind of perovskite NCs.Chapter 3: High-efficiency hybrid solar cells based on polymer/PbS_xSe_1-x nanocrystals.A record-high PCE of 5.50% and FF of 67% were achieved in our hybrid solar cells.The remarkable device efficiency can partially be attributed to the excellent photovoltaic properties of the PbS_xSe_1-x NCs,which show improved performance than either the conventional PbS or PbSe NCs.Furthermore,we thoroughly investigated the evolution of the three-dimensional morphology with the polymer/NCs blend ratio and confirmed the forming of vertical phase segregation.After depositing one more layer of NCs on top of the blend film,a desired device architecture with the vertical D-D:A-A structure was obtained,which facilitates charge separation and transport,leading to greatly improved device performance.Chapter 4: Pulsed lasers employing solution-processed plasmonic Cu_3-xP colloidal nanocrystals.Colloidal Cu_3-xP NCs with accurately controlled sizes were successfully synthesized.These plasmonic Cu_3-xP NCs show tunable localized surface plasmon resonance?LSPR?absorption from 1390 nm to 1710 nm,which covers all the telecommunication C to L bands.In addition,we discovered a facile approach to modify the NCs surface condition by thermal treatment,resulting in easy modulation of the NCs' LSPR amplitude,nonlinear optical absorption and transient dynamical response.After systematical investigation,we demonstrated for the first time that self-doped plasmonic Cu_3-xP NCs could be used as simple and effective nonlinear absorbers in a 1.5 ?m high-energy Q-switched laser.Compared with other Q-switchers,Cu_3-xP NCs exhibit comparable nonlinear optical properties and device performance as well as better compatibility to optical components.Our work suggests that heavily doped plasmonic NCs can work as low-cost,solution-processed new generation nonlinear optical materials for applications in signal processing and optical communications.In summary,starting from basic material synthesis,we focus on the methods for adjusting the properties of three kinds of NCs materials and their effects on related device performance.We have revealed some correlations between NCs synthesis and the final device performance,which will promote the fundamental and applied research in corresponding nano-science.