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  • 學位論文

應用於發光二極體之全無機鈣鈦礦量子點

All-Inorganic Perovskite Quantum Dots for Light-Emitting Diodes

指導教授 : 劉如熹

摘要


白光發光二極體應用於液晶顯示器之背光源為當代趨勢,而色純度與色域面積為高品質背光源之重點指標,其影響顯示器之色彩表現。綠色CsPbBr3鈣鈦礦量子點,因其具半高寬約20 nm之窄譜帶與高量子效率之優勢,而被視為應用於廣色域背光顯示最具希望之窄譜帶綠色螢光材料。然因量子點存在表面缺陷、熱穩定性差與液態不易封裝之缺點,使其於白光發光二極體之應用受限。本研究乃提出三步驟合成鈣鈦礦量子點之複合材料以獲得高量子效率且穩定之窄譜帶綠色螢光材料。所得聚合物包覆之多孔性鈣鈦礦量子點粉末具高達63%之絕對量子效率、較佳之熱穩定性與耐水性,且其由溶液態轉變為如同螢光粉之固體粉末,其可應用於背光顯示之晶片型白光發光二極體,色座標為(0.271,0.232),此白光發光二極體通過彩色濾光片後,色域面積約為NTSC標準之102%。 此外,量子點式有機發光二極體因具更廣之色域面積而獲得更佳之顯示品質,近年亦愈來愈受重視,其可應用於液晶顯示器之背光源,或具有機發光二極體之主動發光顯示原理之顯示器,後者被視為下一世代之顯示器。CsPbBr3鈣鈦礦量子點亦具應用於此電致發光元件之潛力,然難以兼顧元件表現與環境保護。為達此平衡,本研究亦以簡單之熱注射方式合成Cs(Pb1-xSnx)Br3,以較穩定之Sn4+部分取代有毒之Pb2+。其中Cs(Pb0.67Sn0.33)Br3樣品之絕對量子效率從CsPbBr3樣品之45%提高至83%。並由飛秒瞬態吸收、時間解析螢光光譜與單粒子光譜之分析鑑定,獲得量子效率提升之原因為Sn4+之取代使鈣鈦礦量子點中帶電激子(trion)之形成減少。此高量子效率之Cs(Pb0.67Sn0.33)Br3製成之量子點式有機發光二極體之元件表現明顯提升,此元件放光波長為517 nm,電流效率為11.63 cd/A,外部量子效率為4.13%,此元件表現為目前含錫鈣鈦礦量子點式有機發光二極體中表現最優異者。

關鍵字

發光二極體 鈣鈦礦 量子點

並列摘要


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, a three-step treatment of perovskite CsPbBr3 QDs toward high brightness and stable narrow-band green emission was investigated. After the treatment, a robust and stable narrow-band perovskite mesoporous-CsPbBr3/SDDA@ PMMA powder was obtained. The powder exhibited several advantages, including high absolute PLQY of 63%, improved thermal stability, and water resistance. A white LED used in backlight display was successfully fabricated with color coordinates of (0.271, 0.232) that passed through RGB color filters with an NTSC value of 102%. Moreover, CsPbBr3 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. This trion-formation suppression by Sn4+ substitution consequently increased the performance of QLED devices based on these highly luminescent Cs(Pb0.67Sn0.33)Br3 QDs, exhibiting a central emission wavelength of 517 nm, a current efficiency of 11.63 cd/A, and an external quantum efficiency of 4.13%, which to date are the highest values among the reported Sn-based perovskite QLED devices.

參考文獻


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