Study On The Stability Of Perovskite Quantum Dots And Its Electroluminescent Diodes

Due to large absorption cross section,narrow emission,high purity colour excellent photoelectric property,quantum dots?QDs?have regarded as superexcelllence materials.The power conversion efficiency of perovskite solar cells have exceeded 20%and been broken new regards in recently.Combining the merities between QDs and perovskite,lead halide perovskite nanocrystals have attracted widespread attention by researchers domestic and oversea.However,the stability of the perovskite material emergied extremely poor,whether bulk material,two-dimensional nanosheet and a nanowire,or a zero-dimensional quantum dot.This crystal structure is inherently sensitive to polar solvents and oxygen in ambient,which will seriously affect the photoeletricty device with perovskite quantum dot.This article explores mainly how to improve the stability of perovskite quantum dots and the performance of their electroluminescent diodes from Chapters 3 to 5.In Chapter 3,we compare the solvent of acetonitrile and toluene with the popular DMF and toluene solvents used for the room temperature synthesis of perovskite nanocrystals.We found that the perovskite quantum dots synthesized using acetonitrile and toluene can maintain their stability and excellent optical properties for several more months.This new synthesis strategy has ability to prepare the full-spectrum FAPbX₃?X=Cl,Br,I,mixed Cl and Br or mixed Br and I?,employing FAPbBr₃ nanocrystals whose quantum yield achieve 88%as a light-emitting layer.The highest external quantum efficiency of this electroluminescent diode was 2.8%,and the maximum fluorescence was 403 cd/m².In order to obtain good crystallinity and monodisperse QDs,thermal injection method is employed to synthesize FAPb Br₃ quantum dots in Chapter 4.However,the use of the traditional room temperature liquid state ligands oleic acid?OA?and oleylamine?OAm?makes it possible for the ligands on the surface of quantum dots and free ligands to undergo a dynamic exchange process.This dynamic exchange easily leads to dynamic equilibrium shifts as the environment changes,resulting in the shedding of a large number of ligands on the surface of the quantum dots,and finally agglomeration and precipitation.Depending on the phenomenon,we used relatively high melting point ligands octadecylamine?ODA?and stearic acid?SA?as ligands,and the synthesized perovskite quantum dots were solidified,which prevents the dynamic exchange of ligands on the surface of the quantum dots and free ligands in the solvent.This initial product can maintain the crystal stability and optical properties in the following months.The use of high melting point ligands for the synthesis of high crystalline,monodisperse perovskite QDs provides a new idea for storage.At the same time,we prepared high-performance electroluminescent diodes using purified perovskite quantum dots.Furthermore,the performances of PVK and TFB hole transport layers in perovskite quantum dot electroluminescent diodes were compared.The external quantum efficiency of TFB as the hole transport layer is3.02%,the luminous intensity is 3124 cd/m2,the external quantum efficiency of PVK as the hole transport layer is 4.08%,and the luminous intensity is 4752 cd/m2.Such external quantum efficiency and luminous intensity exceed most of the literature reports.In Chapter 5,we developed a strong coordination organic phosphine?TBP?as a ligand to synthesize iodine-containing perovskite quantum dots.Because the fluorescence emission wavelength of the FAPb I₃ nanocrystals reaches the near-infrared range,it may not be suitable as a light emitting diode.In this study,we used CsPbI₃,a fluorescent red emitting light,as a research object to investigate the solution optical properties and stability of TBP-CsPbI₃ quantum dots synthesized by TBP as ligands,and the stability of quantum dot films.The data demonstrates that the iodine-containing perovskite nanocrystals can maintain a stable performance for at least 30 days using a strong coordination organophosphorus ligand.The performances of the PQLEDs with the traditional ligand synthesized perovskite quantum dots OAM-CsPbI₃ and TBP-CsPbI₃ as light-emitting layers were compared.The external quantum efficiency of the PQLED with TBP-CsPb I₃?2.000%?as a light-emitting layer is much greater than that of the PQLED with OAM-CsPbI3?0.198%?as the light-emitting layer.