【Adv.Funct.Mater.】苏州大学张秀娟|突破极限！首创微腔结构让红光高偏振发光比率飙升至228.1#

Design principles and theoretical simulation of BMeOPhFO. (a,b) Design strategies of highly intrinsically polarized emission OSSCs vs. conventional emissive OSSCs. The arrows denote the orientations of TDMs. (c) Chemical structure of the BMeOPhFO molecule, which adopts a D-A-D skeleton. (d) Contour plots of the X, Y, and Z components of the TDM density within a single unit cell. (e) Computed electron–hole distributions for the LE and CT states in a BMeOPhFO hexamer, along with the intermolecular transfer integrals for the HOMO (_t_H) and LUMO (_t_L) between adjacent molecules. (f) Energetic landscape and electronic couplings among diabatic states for the BMeOPhFO hexamer.#

Structural and crystallinity characterization of BMeOPhFO SCs. (a) Schematic illustration of the antisolvent vapor-assisted method used for SCs growth. (b) Fluorescence microscopy image of a SC under 365 nm light excitation. (c) High-resolution AFM image of the crystal surface. Inset: corresponding FFT pattern. (d) SAED pattern of a SC. Inset: corresponding TEM image. (e) XRD pattern of a SC. (f) In-plane φ-scan of the (020) reflection. (g) ADPL intensity of p-polarized emission from the SCs.#

在材料制备与表征方面，如图2所示，研究团队利用反溶剂蒸汽辅助法成功生长出了表面极度平整、形态高度规整的二维菱形BMeOPhFO单晶。在紫外光激发下，该单晶展现出极其均匀且强烈的光致红光发射。通过交叉偏振光学显微镜和透射电镜下的选区电子衍射分析，明确了其单晶的各向异性本征，并精确确定了菱形晶体的长对称轴对应于晶体的c轴，短对称轴对应于b轴。此外，变角光致发光测试证实该晶体具有高达91%的水平偶极子比率，这不仅从根本上强化了表面出光的固有偏振度，还大幅提升了晶体的光耦合输出效率。

Intrinsic polarization characteristics of BMeOPhFO SCs. (a) Optical microscopy image of a representative BMeOPhFO SC, showing the defined 0° reference axis (white dashed line) and the crystallographic c- and _b-_axes, which correspond to the directions of maximum and minimum polarized emission, respectively. Polar plots of the Raman intensity at 1599 cm−1 as a function of polarization angle in the (b) parallel and (c) cross polarization configurations. (d) Angle-resolved absorbance of BMeOPhFO SC at an incident wavelength of 540 nm. (e) PL spectra of a BMeOPhFO SC measured with linear polarization aligned the c-axis (maximum) and b-axis (minimum) directions. (f) Comparison of the intrinsic PR values and PL peak wavelengths of BMeOPhFO SCs with those of previously reported OSSC polarized emitters. (g) Contour plot of the normalized polarization-dependent PL intensity as a function of emission wavelength and polarization angle. The 0° reference direction is identical to that defined in panel (a). (h) Polar coordinate plot of the PL peak intensity recorded at varying polarization angles. (i) Spatial map of the PR extracted from measurements performed over a 50 µm × 50 µm area within a single BMeOPhFO SC.#

为了进一步揭示宏观光学各向异性与微观晶体结构的内在联系，如图3所示，团队对该单晶进行了角度分辨偏振拉曼光谱和偏振吸收光谱测试。实验以特定角度为参考，随着样品在入射光轴下的旋转，拉曼峰强呈现出完美的周期性三角函数调制，深刻反映了晶格内部强烈的各向异性分子振动。偏振吸收光谱和偏振发光光谱表现出高度的一致性，其发光强度在c轴方向达到极大值，在b轴方向降至极小。得益于极高的取向规整度，BMeOPhFO单晶取得了高达97.4的光致发光偏振比，远远超越了此前报道的所有同类有机单晶材料。值得注意的是，实验中还捕捉到了另一种表现为针状形貌的橙光多晶型相，由于其内部存在强烈的 intermolecular 电子耦合，导致其偏振比骤降了约36倍，这一对比有力地证明了弱的超分子电子耦合对维持高偏振发射的决定性作用。

EL characteristics of BMeOPhFO SC-based LP-LED. (a) Schematic illustration of the device fabrication process. (b) Cross-sectional SEM image of a representative device. (c) EL spectra recorded at varying applied voltages. Inset: Optical image of the operating device. (d) EQE as a function of applied voltage. (e) CIE color coordinates of the device, confirming pure red emission. (f) Contour plot of normalized polarization-dependent EL intensity as a function of wavelength and polarization angle. (g) Polarization-resolved EL spectra measured parallel to the crystallographic c-axis (maximum intensity) and b-axis (minimum intensity).#

为了探索该高偏振红光单晶在实际器件中的应用潜力，如图4所示，研究团队巧妙利用自主研发的液体绝缘层桥接技术成功构筑了基于BMeOPhFO单晶的线偏振发光二极管（LP-LED）。该结构有效地防止了因单晶边缘厚度剧烈起伏而导致的短路或开路失效。器件表现出极佳的电致发光光谱稳定性，在25至40伏的宽电压工作区间内，始终保持稳定的纯红光发射，最大亮度达到每平方米244坎德拉。更令人振奋的是，由于单晶极高的固有各向异性，该器件在没有任何外部偏振过滤器的协助下，直接输出了高纯度的线偏振红光，其电致发光偏振比达到了62.7，达到了目前红光电致发光器件的领先水平。

Spectral narrowing and enhanced polarized emission in BMeOPhFO SC-based microcavity device. (a) Schematic illustration of the PL measurement configuration, with the BMeOPhFO SC opaque (bottom) and semitransparent (top) Ag mirrors forming a Fabry-Pérot cavity. (b) PL spectrum of the BMeOPhFO SC, showing microcavity-induced spectral narrowing from broadband spontaneous emission to a sharp resonant peak. (c) Polarization-resolved PL spectra measured along the crystallographic c-axis (maximum intensity) and b-axis (minimum intensity). (d) Device architecture of the LP-LED based on BMeOPhFO SC with a microcavity architecture. (e) EL spectrum of the microcavity device under operation at 38 V. (f) Polarization-resolved EL spectra recorded along the c-axis (maximum) and b-axis (minimum) directions. (g) Benchmark comparison of PR and emission FWHM with previously reported polarized emitters, encompassing single crystal (SC) and oriented thin-film (TF) systems across organic (blue), inorganic (green), and organic-inorganic hybrid (grey) materials, for both PL and EL performance.#

最后，为进一步榨干该体系的偏振潜力并克服发光带宽较宽的固有缺陷，如图5所示，研究团队在器件中精细集成了由全反射底电极和半透明顶电极构筑的法布里-珀罗光学微腔结构。利用微腔独特的光学反馈与共振模式选择效应，器件优先放大并增强了沿主偏振轴方向的辐射。这一设计带来了惊人的双重提升：一方面，光致发光和电致发光的偏振比分别被戏剧性地泵升至228.1和187.0的创纪录高度；另一方面，原本较宽的自发辐射光谱被强烈压缩，其发光半峰全宽分别骤降至7.8纳米和11.7纳米。这一杰出的性能指标打破了目前各向异性偏振发光材料的极限纪录，兼顾了极致的偏振纯度与光谱色纯度。