The Investigation Of Perovskite Quantum Dots And Related Light Emitting Diodes Via Surface Modification

Due to their outstanding optoelectronic properties,metal halide perovskite has attracted great attention from researchers and is a candidate for the next-generation semiconductor materials,especially applied in those areas like solar cells,low-threshold lasers,photodetectors and light-emitting diodes?LEDs?,etc.Furthermore,people find that the quantum dots?QDs?of metal halide perovskite materials have even more extraordinary characteristics.Since it was synthesized firstly in 2012,the emission performance and the stability of perovskite QDs have been greatly improved,indicating unexpected potential of perovskite QDs in optoelectronic applications.Meanwhile,devices based on perovskite QDs have been developed at a rapid pace.Electroluminescent LEDs based on perovskite QDs have much better performance with higher external quantum efficiency of 21.3%now than that of 0.1%in 2014.Although people have spared no effort to boost the perovskite performance and already obtained great achievements,there are still many problems left unsolved,one of which is that people still lack the ability to modify the surface of perovskite QDs.Owing to the ionic nature of metal halide perovskite,it has much complicated and dynamic surface states.Therefore,in this work,we took further analysis and sufficient experimental testaments.And finally,we succeeded in acquiring high-quality perovskite QDs via surface modification with ideal optical and electrical properties.Here is the main work:1.The Investigation of Perovskite QDs'Properties via Surface ModificationFirst of all,our work found out that inorganic salts had very interesting interaction with CsPbCl_xBr_3-x perovskite QDs.To have a further understanding of such mechanism,various characterizations were used.With the help of X-ray photoelectron spectra,X-ray diffraction patterns and high-resolution transmission electronic microscopic images,etc.,we excluded the possibility of dopant like metal element.Moreover,Fourier infrared spectra reveals the unchanged surface ligands which denied the ligand exchange process.And finally,the observation of absorption and emission spectra and X-ray photoelectron spectra demonstrated the peeling process caused by nitration salts to unexpected surface defects and vacancies,like lead atoms,uncoordinated lead ions and excess cesium ions,etc.After treatment,the quantum yield of blue perovskite QDs reached 85%.And the analysis of recombination dynamics shows the increase of recombination rates and the decrease of non-recombination rates.The method and design of our work is able to enlighten new ideas and approaches for the improvement of future blue perovskite LEDs.2.The Investigation of Perovskite QD Light Emitting Diodes via Surface ModificationIn this work,according to the surface configuration of perovskite QDs,we designed a method to modify the ligand density on the surface,which managed to control the interdot distance between QDs.Such variation can not only improve the carrier mobilities in QD film,especially hole mobility,but also balance those mobilities.Based on our experimental results and theoretical analysis,the relationship between QD interdot distance and carrier mobility was convincing.Finally,our device had the max external quantum efficiency of 12.7%and 11%efficiency roll-off.Moreover,our simulation pointed out that it is the uniform carrier distribution caused by balanced mobilities that lowers lower the ratio of Auger recombination.So,our work provided a simple approach to suppress the roll-off issue for perovskite QD LEDs,which is also a perspective for material and device design in the future.Our results paved the way for perovskite QDs to real applications in display and lightning,etc.