Studies On The Performance Of White LEDs Based On Alloy Core/shell Structure Quantum Dots

In recent decades,the application of quantum dots(QDs)in Light-Emitting Diode(LED)has attracted much attention.There are two main ways to apply QDs in LED: they can be used as light converters to prepare photoluminescent devices,or active materials for the preparation of electroluminescent devices.In this thesis,the effects of CdZnS/ZnS and CdZnS/ZnSe core/shell alloy QDs on the performance of quantum dot-based photoluminescence white LEDs were studied,as well as those of anodic ITO interface modification on quantum dot-based Electroluminescent LEDs.Quantum dot-based LEDs(QLEDs)with bright white light can be manufactured by integrating the mixture of red,yellow and green CdZnS/ZnSe QDs with blue lightemitting GaN LED chips.Changing the amount of green QDs gradually,their effects on the performance of white LEDs were studied,and the ratio of QDs with different emission wavelengths was identified.The resulted white LED show high luminescence,and satisfied visual properties with a color rendering index(CRI)of85.2,a correlated color temperature(CCT)of 4072 K,a luminous efficacy of optical radiation(LER)of 234.67 lm/W,a color coordinate of(0.35,0.29)when the proportion of red,yellow and green CdZnS/ZnSe QDs is 9 :6 :24,and under a forward bias current of 10 mA.The combination of CdZnS/ZnS and CdZnS/ZnSe QDs were also used to prepare white LEDs.Two-band WLEDs based on blue and yellow QDs and four-band WLEDs based on blue,green,yellow,and red quantum dots were prepared.Both theoretical calculations and experimental results show four-band WLED presented better e luminous performance and visual characteristics than the two-band one.The prepared four-band WLEDs exhibits a scotopic/photopic ratio(S/P)o up to 2.52 at a forward bias current of 60 mA,a CRI of 90.3,a LER of 460.78 lm,and a CCT of5454 K.These results show that CdZnS/ZnS and CdZnS/ZnSe QDs have great application prospects in the preparation of the next generation of high performance and visually friendly white light sources.On the other hand,modifying the electrodes can effectively improve the performance of QLEDs.The anodic ITO interface was modified by the means of solution-immersion,UV illumination and UV illumination solution.The effect of the electrode modification on the reduction of the injection barrier and the injectionefficiency of the hole carriers was investigated.We concluded that the UV illumination solution method can regulate the charge injection barrier more effectively than the methods of solution-immersion and UV illumination,improve the balance of electron-hole injection and has great potential application in improving the performance of the QLEDs.