機械可調自旋金屬有機框架LED

Abstract

本研究提出一種新穎策略，成功以手性金屬有機框架（Chiral Metal-Organic Frameworks, chiral-MOFs）作為自旋選擇性載子注入層，實現無需外加磁場與鐵磁接觸之下的室溫自旋極化圓偏振發光元件。相較於傳統自旋元件仰賴磁性材料進行載子極化的方式，本研究運用 MOF 材料內在的手性結構，透過「手性誘導自旋選擇性（Chiral-Induced Spin Selectivity, CISS）」效應，選擇性的傳輸特定自旋態的電洞，進一步促使量子點層產生顯著的圓偏振電致發光（Circularly Polarized Electroluminescence, CP-EL）。 我們透過水熱法合成對掌結構明確的 D-/L-Eu(Tar)MOFs，並藉由 CD 與 CPL 光譜證實其鏡像手性與優異的圓偏振發光能力（glum ≈ 0.41）。隨後，將其整合於全柔性元件架構中：FITO/SAM (P3HT-COOH)/D- or L-MOF/CdSe QDs/ZnO/Ag，其中自組裝單分子層（SAM）有效提升載子注入效率與介面穩定性，CdSe/ZnS 量子點則提供窄頻寬（FWHM = 27 nm）、高效率的紅光發射。 實驗結果顯示，導入 chiral-MOF 後的元件在 632 nm 發光波長處展現極高的圓偏振度，其圓偏振發光偏極度（PCP-EL）最高可達 ±21.86%，遠優於過去文獻中以有機或無機手性材料構成之 spin-LED 裝置。此外，對照組（未加入 MOF 層）之元件無法產生明顯的圓偏振光，進一步證實 CISS 效應為造成 CPL 發光的關鍵機制。 更進一步地，我們系統性研究了元件在不同彎折曲率下的發光特性變化。隨著曲率半徑由 降低，偏極度由 21.86% 漸降至 13.54%，且該變化為可逆，顯示元件具備優異的力學可調性與穩定性。配合拉曼光譜測量發現，MOF 結構在彎曲時 C–H 鍵振動峰產生藍移，證實其內部結構因機械應力產生局部微調，進一步影響 CISS 效應的強度與發光極化表現。 本研究成功展示以 MOF 為核心的手性自旋選擇材料不僅能實現高效率的自旋注入，亦能在無磁場條件下產生穩定的圓偏振發光。更重要的是，其柔性結構具備機械可調特性，提供一全新自由度以操控發光偏極行為，為可撓式自旋光電子元件、量子資訊傳輸與未來穿戴型光電技術之開發，奠定關鍵基礎。

In this study, we propose a novel strategy to successfully use chiral metal–organic frameworks (chiral-MOFs) as spin-selective carrier injection layers to realize room-temperature spin-polarized circularly polarized light-emitting diode (spin-CP-LED) devices without the need for an applied magnetic field or ferromagnetic contacts. In contrast to conventional spintronic devices that rely on magnetic materials to induce spin polarization, the present study utilizes the intrinsic chirality of MOFs to selectively transport holes in specific spin states through the chiral-induced spin selectivity (CISS) effect, thereby enabling the quantum dot (QD) layer to emit significant circularly polarized electroluminescence (CP-EL). We synthesized D-/L-Eu(Tar) MOFs with well-defined enantiomeric structures via a hydrothermal method, and confirmed their mirror-image chirality and excellent circularly polarized emission capability (glum ≈ 0.41) using circular dichroism (CD) and circularly polarized luminescence (CPL) spectroscopy. These chiral MOFs were subsequently integrated into a fully flexible device architecture: flexible ITO (FITO)/self-assembled monolayer (SAM, P3HT-COOH)/D- or L-MOF/CdSe QDs/ZnO/Ag, where the SAM layer significantly improves carrier injection efficiency and interfacial stability, while the CdSe/ZnS quantum dots provide narrow emission bandwidth (FWHM = 27 nm) and high-efficiency red emission. Experimental results show that the chiral-MOF-integrated device exhibits a remarkably high degree of polarization (PCP-EL) at an emission wavelength of 632 nm, reaching ±21.86%, which is significantly higher than the PCP-EL values reported for spin-LEDs based on organic or inorganic chiral materials. In contrast, the control devices without the MOF layer fail to generate measurable circularly polarized light, further confirming that the CISS mechanism is the primary origin of the observed CP-EL. Furthermore, we systematically investigated the luminescence behavior of the devices under various bending radii. As the curvature radius decreased, the degree of polarization decreased from 21.86% to 13.54%, with the change being fully reversible, indicating excellent mechanical tunability and structural robustness. Raman spectroscopy revealed a blue shift in the C–H vibrational modes of the MOF structure under bending, confirming that localized structural modulation occurs due to mechanical stress, which in turn affects the strength of the CISS effect and the resulting polarization characteristics. In conclusion, this study successfully demonstrates that MOF-based chiral spin-selective materials not only enable efficient spin injection but also allow for stable circularly polarized light emission under ambient, non-magnetic conditions. More importantly, the mechanical tunability of the flexible architecture provides a new degree of freedom for controlling polarization behavior, establishing a solid foundation for the future development of flexible spintronic devices, quantum information technologies, and next-generation wearable optoelectronics.