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Advanced functional materials: fabrication of green thick shell blue InP quantum dot devices

wallpapers News 2020-08-29

qled is a device using quantum dots as light-emitting materials which has the characteristics of wide color gamut high luminous efficiency low power consumption ink-jet printing flexibility so on. As the representative of III - V semiconductor materials InP quantum dots have large exciton Bohr radius strong quantum confinement effect no heavy metals such as mercury cadmium lead excellent stability so they have a wide range of application prospects. Qled display uses QD to emit red green blue colors independently to form a pixel produces color pixels by adjusting the proportion of the three colors. Red green blue light source is very important to display. At present there is a big gap between the performance of blue light qled red light green light which has become one of the main bottlenecks restricting the development of full-color InP qled. At present the mainstream InP synthesis route uses tris (trimethylsilyl) phosphine [(TMS) 3P] as P source. The price of (TMS) 3P is expensive it will produce highly toxic phosphine gas after contacting with air which is not conducive to industrial synthesis.

for this reason Professor Sun Xiaowei of South University of science technology his collaborators used cheap (1 / 80 times) stable tris (dimethylamino) phosphine [(DMA) 3P] as P source to prepare pure blue InP / ZnS quantum dots with an emission peak of 468 nm. By effectively removing zinc stearate residue high efficiency InP blue light qled device was prepared. When

are used to prepare InP / ZnS quantum dots zinc stearate microspheres will be formed after the reaction due to the excessive zinc stearate added in the cladding process. It is difficult to completely remove zinc stearate impurities by centrifugation. Although zinc stearate can be purified with chloroform as solvent the lig on the surface of quantum dots is easy to fall off due to the strong polarity of chloroform which leads to the decrease of QY of quantum dots. In order to completely remove zinc stearate reduce the introduction of surface defects. The team reacted with zinc stearate by adding s-top. Excessive s-top would react with residual zinc stearate to form ZnS monomer. At the same time the ZnS monomer can be coated on the surface of InP / ZnS quantum dots to increase the thickness of InP / ZnS shell. When the thickness of the shell increases the stability of QDs is also improved. After 10 hours irradiation with 365 nm UV lamp (8 MW / cm2) the QY of InP / ZnS / ZnS quantum dots decreased to 50% while the QD of InP / ZnS quantum dots decreased to 23%.

Fig. 1 Schematic diagram stability test of thick shell InP / ZnS / ZnS quantum dots. Compared with InP / zns-qled the maximum current efficiency of

InP / ZnS / zns-qled increases from 1.3 CD / A to 3.6 CD / A EQE increases from 0.6% to 1.7% the brightness increases from 25 CD / m2 to 140 CD / m2 at 6 v. The current density increases from 32 MA / cm2 to 125 MA / cm2 at 8 v. At the same time due to the improvement of carrier injection efficiency the turn-on voltage decreases from 4.2 ev to 3.1 ev. There are two main reasons for the improvement of device performance. Firstly the increase of the thickness of the QD shell can reduce the energy transfer in the QD. Secondly the residual zinc stearate was reacted with s-top to improve the hole injection efficiency. This research has greatly promoted the progress of blue InP qled in the field of light-emitting display.

Figure 2 (a) energy level diagram of qled; (b) PL El spectra of InP / ZnS / ZnS QDs; device characteristics of InP / ZnS InP / ZnS / ZnS; (c) current efficiency current density curve; (d) EQE current density curve; (E) current density voltage curve; (f) brightness voltage curve

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