| Summary: | 碩士 === 國立臺灣大學 === 化學研究所 === 106 === White light-emitting diodes (LEDs) is widely used as backlighting components in the modern liquid-crystal display (LCD). For high-quality backlight, color saturation and color gamut are the key indicators, which affect the color performance display devices. Perovskite CsPbBr3 quantum dots (QDs) are regarded as the most promising narrow-band green-emitting material for wide-color-gamut backlight displays because of their high photoluminescence quantum yield (PLQY) and the narrow-band emission with a full width at half maximum (FWHM) of ∼20 nm. Despite their growing popularity, CsPbBr3 QDs have several shortcomings such as the existence of surface trap states, poor thermal and aqueous stability, and the solution QDs are unsuitable for direct use in on-chip white LEDs. Here, the surface treatment of perovskite CsPbBr3 QDs with thiocyanate salts (SCN-) toward high brightness and stable narrow-band green emission was investigated. After the treatment, a high quantum yield and stable narrow-band perovskite CsPbX3-SCN was obtained. The product exhibited several advantages, including high absolute PLQY of 94%, enhaced photoluminescence intensity, and air stability.
Moreover, CsPbBr3-SCN perovskite QDs are potential emitters for QLED electroluminescent displays. However, balancing their performance and their environmentally friendly property is challenging. To achieve such balance, we demonstrated an easy hot-injection method to synthesize Cs(Pb1-xSnx)Br3 QDs by partially replacing the toxic Pb2+ with the highly stable Sn4+. Meanwhile, the absolute PLQY of Cs(Pb0.67Sn0.33)Br3 QDs increased from 45% to 83% compared with CsPbBr3. Based on a femtosecond transient absorption, time-resolved PL, and single-dot spectroscopies, we conclude that the PLQY enhancement is due to the reduction of trion formation in perovskite QDs with Sn4+ substitution.
Moreover, the CsPbBr3-SCN solution that surface treatment with thiocyanate salt increased the performance of QLED devices based on these highly luminescent cesium lead halide perovsike QDs, exhibiting a central emission wavelength of 516 nm, a current efficiency of 4.2 cd/A, and an external quantum efficiency of 1.4% which is the higher values among the CsPbBr3 perovskite QLED devices.
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