Luminous Stability Of Perovskite Quantum Dots And Fabrication Of High Purity Yellow Light-Emitting Diodes

Quantum dots are nanoscale particles composed of limited numbers of atoms where the motions of electrons are confined in all directions.One of the most outstanding properties of quantum dots is the quantum confinement effect,where their band gap would be altered along with the shrinking or expansion of particles.In addition,quantum dots have advantages of tunable emission wavelength,narrow bandwidth and high photoluminescence（PL）efficiency.The Inorganic cesium lead halide（CsPbX3）perovskite quantum dots attracted intense attention for their combined superior optical performance of both QDs and halide perovskite which exhibit great potential in the field of LEDs,lasers and solar cells.In this dissertation,beginning with the study synthesis method of CsbX₃ quantum dots,we studied the stability of CsPbBr₃ QDs and fabricated a QD-converted yellow LEDs.Main achievements are listed as followed:（1）The inorganic CsPbBr₃ perovskite QDs were prepared by a hot-injecting method use Cs₂CO₃ as Cs-precursor。The quantum efficiency of the perovskite CsPbBr₃ QDs solution was about 90%.The absorption peak was at 515 nm while the PL peak located at 520 nm.The CsPbBr₃ QDs had a high crystallinity and half-maximum（FWHM）was about only 20 nm,indicating high-purity green emission.We also used Cesium Stearate as Cs-precursor for Synthesis of various CsBrX₃（X=Cl、Br、I）quantum dots。When the molar ratio of Br/I is 0.55/0.45,The PL peak of CsPb(Br_0.55I_0.45)₃ QDs is 570 nm and full width at half maximum（FWHM）of the PL peak is 25 nm.CsBrX₃ demonstrate excellent optical performance.（2）We tried to study the optical stability of CsPbBr₃ QDs under different atmosphere condition.We prepared some CsPbBr₃ QDs films by spin-coating method.The PL spectra were measured in air and nitrogen.We found that luminous intensity of QDs decrease fast in oxygen and the intensity decrease is not reversible.In the nitrogen,we found that the luminous intensity of CsPbBr₃ QDs are much more stable than in air.We used atomic layer deposition（ALD）to grow an amorphous Al₂O₃ layer on the CsPbBr₃ QDs film.Trimethylaluminum（TMA）and O₂ plasma were used as the Al and O precursors for ALD,respectively.These CsPbBr₃ QD/AlO_x show an exceptional stability against exposure to air and water.（3）A novel heat insulation structure was designed for the QD-converted yellow LEDs.In this structure,a silicone layer was set on top of the GaN LED chip to prevent directly heating of the QDs by the LED chip.Then the CsPbBr_0.55I_0.45 QDs were filled in the bowl-shaped silicone layer after ultrasonic dispersion treatment.Finally,an Al₂O₃ passivation layer was grown on the QDs layer by Atomic Layer Disposition at 40℃.The highly pure yellow LEDs with an emission peak at⁵70nm and a full width at half maximum of 25 nm were achieved.The chromaticity coordinates of the QD-converted yellow LEDs（0.4920±0.0017,0.4988±0.0053）showed almost no variation under driving current from 5 mA to 150 mA.During an operation period of 60 minutes,the emission wavelength of the yellow LEDs showed no distinct shift.Moreover,the luminous efficiency of the QD-converted yellow LEDs achieved 13.51 lm/W at 6 mA.These results demonstrated that CsPbBr_0.55I_0.45 QDs and the heat insulation structure are promising candidate for high purity yellow LEDs.