Controllable Synthesis Of CdZnS(Se) Alloyed Core-shell Quantum Dots And Its Application In Photoelectric Devices

Colloidal quantum dots?QDs?have been regarded as most promising candidate semiconductors due to their unique properties,including high quantum efficiency,high color purity,low-cost solution processability,as well as an easily tunable emission wavelength.They are considered to be alternative emissive materials for next-generation light-emitting diodes?LEDs?in lighting and display applications.However,there are several factors that limit the performance of QLEDs,such as nonradiative recombination,energy transfer,and field-induced quenching.This thesis focuses on the controllable synthesis of novel CdZnS?Se?alloyed core-shell quantum dots and the development of their optoelectronic devices.The composition and structure of alloy quantum dots were carefully designed by using various synthesis methods to reduce the lattice mismatch.We constructed an alloyed core-shell quantum dot system with high quantum yield,adjustable luminescence spectrum,controllable energy level structure and interface matching.The interaction mechanism,the relationship between the microscopic composition of quantum dots and the macroscopic properties of quantum dots were revealed by inducting and analyzing a large number of experimental data.?1?A simple one-step method for synthesizing thick-shell blue CdZnS/ZnS core-shell quantum dots was developed.Through the rapid injection of zinc oleate power/S TBP solution,a ZnS shell layer was coated on the core layer without the need for a purification process,and finally a core-shell quantum dot is formed.The thickness of the shell was adjusted by changing the injection amount of zinc oleate/S TBP solution.Thanks to the thick shell layer,which can effectively suppress non-radiative recombination for the quantum dot system,the core-shell quantum dots with 10 ZnS shell layers exhibited pure blue light emission performance?⁴55 nm?and narrow emission lines?full width at half maximum of emission peak 17.2 nm?,with high quantum yield?92%?after optimization of the synthesis process.?2?We proposed a cation-assisted method to prepare a new type of CdZnSe alloyed luminous core starting from CdSe core,and finally form a ZnCdSe/ZnSe core-shell quantum dot.Studies showed that the quantum dot system exhibited pure red light emission performance?⁶30 nm?and narrow emission lines?full width at half maximum of emission peak 17.1 nm?,with high quantum yield?99%?after optimization of the synthesis process.We attributed the improved monodispersity of the QDs to the higher growth rate of smaller CdSe cores than larger ones with alloying process for new emitting alloy CdZnSe cores.We expect that our study on cation exchange assisted synthesis for controlling the emission line widths of the QDs could be extended to the high-quality green and blue ones beyond currently achieved.?3?We treated the CdZnSe/ZnSe core-shell quantum dot system with an anionic passivator TBP to remove excess Se on the surface of the quantum dots,thereby significantly improving the quantum yield of the quantum dots.In addition,the study also found that with the introducing TBP,the CdZnSe/ZnSe quantum dot system did not undergo significant fluorescence quenching even at high temperatures?310 ^oC?.The quantum dot-based light-emitting diode device exhibits good optoelectronic performance with a current density maximum of 1679.6 mA/cm²,an EQE maximum of 15%and a current efficiency of 14.9 cd/A.?4?A new type-II Cd_0.1Zn_0.9S/ZnSe core-shell quantum dot system was develpoed.By adjusting the energy-level structure of the core-shell quantum dots so that the wave functions overlap between electrons and holes was reduced,leading to a significant increase in the fluorescence lifetime.The as-prepared core-shell quantum dots delivered a quantum yield of 75.4%?as far as we know,this performance is the highest yield of type-II quantum dot systems?.In particular,through in-depth research,we found the intrinsic relationship between the adjustable range of the emission peak of the core-shell quantum dots and the arrangement of energy levels.At the same time,we explored their applications to quantum dot light emitting diodes and quantum dot solar cell devices.As an important research part in the field of quantum dots,alloy quantum dots are in the initial stage of development,and there are also some problems that need to be solved.However,a large number of efficient quantum dot optoelectronic devices are bound to emerge in future with the development of nano-synthesis technology,the improvement of quantum dot synthesis methods,the deep understanding of quantum dot performance and the advancement of device technology.