零維鈣鈦礦發光材料之合成、鑑定與發光二極體應用

鈣鈦礦材料因其出色之光學性能於發光領域引起廣泛之關注，例如窄發射光譜、可調放光波長、高光致發光量子效率(photoluminescent quantum yield; PLQY)等。然而鈣鈦礦奈米晶體於熱、氧氣、水氣與光照輻射之低耐受性限制其進一步應用。近年來，因零維鈣鈦礦材料具更佳之穩定性且其發光機制備受爭議而成為研究熱點，故本研究著重零維鈣鈦礦材料之相關研究。本研究主要分為四步驟，分別為CsPbBr3/Cs4PbBr6鈣鈦礦材料之發光機制研究、電致發光二極體應用、連續式生產製程調控與延展零維鈣鈦礦研究至CsPbI3/Cs4PbI6晶體。為探解Cs4PbBr6零維鈣鈦礦晶體之發光機制，本研究分析CsPbBr3與Cs4PbBr6之變溫光譜特性推斷，內嵌於Cs4PbBr6基質之孤立CsPbBr3奈米顆粒為其強烈綠色發光之來源。該Cs4PbBr6晶體於低溫下未發現波長紅移之超螢光放射，故證實此些內嵌之CsPbBr3奈米顆粒非游離態之雜相。高解析穿透式電子顯微鏡(High-resolution transmission electron microscope; HRTEM)亦證實，Cs4PbBr6晶體具內嵌之CsPbBr3奈米粒子，其平均直徑約為3.8 nm且彼此分離未見團聚。故此材料應稱為CsPbBr3/Cs4PbBr6複和奈米晶體。為進一步探索CsPbBr3/Cs4PbBr6鈣鈦礦奈米晶體應用於新穎顯示器之可能性，本研究藉調控PbBr2前驅體之SnBr2取代比例，利用熱注射法成功合成平均粒徑13.9  0.2 奈米之CsPbBr3/Cs4PbBr6奈米晶體。將所獲之CsPbBr3/Cs4PbBr6 奈米晶體應用於量子點式有機發光二極體(quantum dot light emitting diodes; QLED)元件，其最大電流效率(current efficiency; CE)為4.89 cd/A，外部量子效率(external quantum efficiency; EQE)為1.74%，此為目前已發表之應用CsPbBr3/Cs4PbBr6奈米晶體封裝之最佳電致發光二極體。欲開展CsPbBr3/Cs4PbBr6零維鈣鈦礦材料之商業應用，連續式生產製程乃其中之關鍵，故本研究利用微流道合成系統調控製程以連續生產CsPbBr3/Cs4PbBr6晶體。將所得之CsPbBr3/Cs4PbBr6晶體與商用之K2SiF6:Mn4+紅色螢光粉混合，封裝於InGaN藍光晶片製成白光發光二極體(light emitting diodes; LED)元件。此白光發光二極體元件之放光光譜表現優異，於色度坐標展現119%之美國電視標準委員會標準色域面積(National television system committee; NTSC)，證實CsPbBr3/Cs4PbBr6 晶體適用於未來之廣色域背光顯示用發光二極體。基於上述研究成果，本研究亦成功藉微乳膠法合成Cs4PbI6晶體，將零維鈣鈦礦材料之研究擴展至近紅外(near-infrared; NIR)放光波段。根據變溫放光光譜與變壓放光光譜特性，發現其具由紅光至近紅外光之強發光特性，本研究推斷Cs4PbI6晶體之發光中心為內嵌之鈣鈦礦型α-CsPbI3奈米顆粒。經高解析穿透式電子顯微鏡確實觀測得此些內嵌之奈米顆粒，其直徑約5 nm，證實Cs4PbI6晶體之發光機制同Cs4PbBr6一致，此皆為內嵌CsPbX3奈米顆粒之“葡萄乾麵包”狀結構。此外，使用CsPbI3/Cs4PbI6晶體亦成功封裝得適用於生物醫學應用之近紅外次毫米發光二極體(mini-LED)。

關鍵字

鈣鈦礦；零維；發光機制；發光二極體；連續式合成

並列摘要

Perovskite materials attract significant attention in the luminescence field because of their excellent optical properties, such as narrow emission, tunable wavelength, and high photoluminescence quantum efficiency. However, the low stability of perovskite nanocrystals (NCs) against heat, oxygen, moisture, and light irradiation limits their further application. In this thesis, we focused on zero-dimensional perovskite materials, which stand out among the family of perovskite materials because of their high stability and interesting emission mechanism. This research could be divided into four major parts: emission-mechanism study, optical application, mass production of CsPbBr3/Cs4PbBr6 perovskite NCs, and the extension of study on CsPbI3/Cs4PbI6 NCs. For the luminescence mechanism of Cs4PbBr6, we showed that isolated CsPbBr3 nanoparticles embedded within a Cs4PbBr6 matrix give rise to a “normal” green luminescence, whereas superfluorescence at longer wavelengths was suppressed. High-resolution transmission electron microscopy showed that the embedded CsPbBr3 nanoparticles were around 3.8 nm in diameter and were well separated from one another. Thus, this kind of material should be presented as CsPbBr3/Cs4PbBr6. To further explore the possibility of CsPbBr3/Cs4PbBr6 for application in advanced displays, we successfully produced CsPbBr3/Cs4PbBr6 NCs around 13.9 ± 0.2 nm in size by using the hot-injection method with additional SnBr2 in the PbBr2 precursor. The as-synthesized CsPbBr3/Cs4PbBr6 NCs were used to fabricate quantum dot light-emitting diode (LED) devices with the highest current efficiency of 4.89 cd/A and external quantum efficiency of 1.74%. This performance is the best for the CsPbBr3/Cs4PbBr6-based electroluminescence emitters among recently published reports. The mass-production process is the key to commercial application. Thus, a microfluidic synthesis process was applied to continuously produce CsPbBr3/Cs4PbBr6 powder. To demonstrate the potential application of CsPbBr3/Cs4PbBr6 powder, the sample was fabricated with K2SiF6:Mn4+ red-emission phosphor onto InGaN blue chips as white LEDs (WLEDs). Our WLED device achieved a high National Television Standards Committee value of 119% for backlight display, indicating that the CsPbBr3/Cs4PbBr6 powder is a promising material for future applications. To extend the research on zero-dimensional perovskite to near-infrared (NIR) emission, Cs4PbI6 was successfully synthesized. Strong red to NIR emission properties were detected, and the optical emission centers of Cs4PbI6 were identified to be numerous embedded perovskite-type α-CsPbI3 nanoparticles (~5 nm in diameter) based on investigations of temperature- and pressure-dependent photoluminescent properties. High-resolution transmission electron microscopy was used to detect these hidden nanoparticles and confirmed a “raisin-bread” structure of the CsPbI3/Cs4PbI6 crystals. A NIR mini-LED for the biological application was successfully fabricated using the as-synthesized CsPbI3/Cs4PbI6 crystals.

並列關鍵字

Perovskite ； zero-dimensional ； luminescent mechanism ； light-emitting diodes ； continuous synthesis

參考文獻

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零維鈣鈦礦發光材料之合成、鑑定與發光二極體應用

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