不同維度鈣鈦礦材料於發光二極體之應用

Abstract

金屬鹵化物鈣鈦礦發光二極體（Perovskite light-emitting diodes, PeLEDs）因具備高螢光量子產率（photoluminescence quantum yield, PLQY）、窄半高寬（FWHM）發光、能階可調控性，以及可利用低溫溶液製程等優勢，成為次世代高效率顯示與照明應用的重要候選材料。不同維度的鈣鈦礦材料在光電特性與結構穩定性上展現出顯著差異，進一步決定其在元件應用中的潛力與挑戰。本論文針對三維（3D）、準二維（quasi-2D）以及二維錫基（2D Sn-based）無鉛鈣鈦礦等三種系統，分別發展出具針對性的材料設計與元件工程策略，期以提升PeLEDs在效率、穩定性與實用性上的綜合表現。 在3D全無機PeLED方面，因其具備高載流子遷移率與優異的載子傳輸特性，曾為早期研究之重點，但卻易受濕氣與熱的影響而導致結構崩解與效率衰退。本研究導入具共軛主鏈與極性橋接官能基的高分子中間層，應用於PEDOT:PSS與CsPbBr₃之間，以改善能階對齊、提升界面浸潤性並優化鈣鈦礦薄膜之結晶品質。實驗結果顯示，在最佳化條件下，此設計可將元件之最高亮度提升六倍，外部量子效率（external quantum efficiency, EQE）亦提高至原始裝置的3.6倍，證實高分子中間層於界面修飾之成效。 進一步也針對準二維鈣鈦礦之挑戰來提出解決方法，本研究聚焦於其相位分佈控制與電子注入界面之工程優化。quasi-2D材料內部同時存在多個不同n值的相（n = 1至∞），彼此間之能量傳遞與載子注入效率對元件性能影響深遠。透過引入天然環狀分子添加劑α-與β-環糊精（cyclodextrin）成功調控不同n相之相對含量，其中α-CD可抑制低n相形成、而β-CD有助於穩定中n相並促進能量傳遞效率。此外，利用具有籠狀結構的cryptand分子進一步強化配位能力與晶體均勻性，有效壓抑非輻射複合路徑。配合具導電性且具缺陷鈍化能力之磷氧化物（PPT與PPF）界面層設計，本研究成功製備出亮度達73,897 cd/m²、EQE超過10%的quasi-2D PeLED元件，並顯著抑制高電流密度下的效率衰退（efficiency roll-off），展現跨尺度相位與界面工程之協同優勢。 而在面對鉛毒性所帶來之環境與健康疑慮，無鉛鈣鈦礦材料逐漸受到重視，其中以錫（Sn）為B位金屬的二維鈣鈦礦材料具備可比擬鉛材料之能帶結構與載流子特性。然而，Sn²⁺易氧化為Sn⁴⁺且晶化速率過快，導致薄膜缺陷密度高、元件穩定性差。為克服此一挑戰，本研究提出結合天然抗氧化劑維生素C（ascorbic acid, VitC）與螯合劑18-Crown-6之雙添加劑策略，兩者可分別抑制氧化反應與捕捉過量離子，有效降低缺陷密度與提升薄膜緻密性與均勻性。實驗結果顯示，優化後元件之EQE由原始的0.21%提升至1.87%，亮度提升近四倍，並展現良好之操作穩定性，證明此策略於無鉛紅光PeLED具高度潛力。 綜合以上，本研究針對不同維度鈣鈦礦材料發展出具系統性與針對性的設計策略，涵蓋高分子界面修飾、環狀分子相位調控、無鉛系統穩定化與多功能界面層應用，成功實現具高效率與高穩定性之PeLED元件，為推動鈣鈦礦光電材料實用化與環境友善化之重要里程碑。

Metal halide perovskite light-emitting diodes (PeLEDs) have emerged as promising candidates for next-generation display and lighting applications due to their high photoluminescence quantum yield (PLQY), narrow emission bandwidths, and low-temperature solution processability. However, PeLEDs based on different perovskite dimensionalities—three-dimensional (3D), quasi-two-dimensional (quasi-2D), and two-dimensional (2D) lead-free tin-based systems—each face distinct challenges related to efficiency, stability, and material control. This dissertation presents a series of dimension-specific material and device engineering strategies aimed at overcoming these bottlenecks and improving the performance of PeLEDs. In the 3D PeLED system, we introduce conjugated polymeric interlayers bearing polar-bridged side groups to tailor the energy-level alignment and crystallization behavior between PEDOT:PSS and CsPbBr₃. This interfacial modification significantly enhances hole injection and film morphology, yielding a sixfold increase in luminance and a 3.6-fold improvement in external quantum efficiency (EQE) compared to the control device. For quasi-2D perovskites, phase control and interfacial optimization are crucial. We employed cyclic molecular additives such as α-/β-cyclodextrins and cryptands to regulate the distribution of different n-phases, enhance energy transfer, and suppress nonradiative losses. Furthermore, we introduced multifunctional phosphine oxide additives (PPT and PPF) at the electron transport interface to facilitate electron injection and defect passivation. This comprehensive approach enabled quasi-2D PeLEDs to achieve an EQE exceeding 10% and luminance over 73,000 cd/m², while effectively mitigating efficiency roll-off under high bias conditions. To address lead toxicity, we explored 2D Sn-based PeLEDs as an alternative. A dual-additive strategy combining ascorbic acid (Vitamin C) and 18-crown-6 was developed to prevent Sn²⁺ oxidation and trap formation, thereby improving film quality and device stability. The resulting devices exhibited an enhanced EQE from 0.21% to 1.87%, along with improved operational stability, validating this approach for efficient red-emitting, lead-free PeLEDs. In summary, this study provides a comprehensive framework for dimension-dependent optimization of perovskite optoelectronic materials, integrating additive engineering, phase control, and interfacial design. The results demonstrate significant advances in efficiency, stability, and structural tunability, paving the way toward practical and environmentally friendly PeLED technologies. Overall, this work presents a unified framework for optimizing perovskite LEDs across varying structural dimensionalities, offering practical solutions to enhance efficiency, phase purity, and operational robustness for future commercial applications.