聚苯撑苯并双噁唑的电致发光

Electroluminescence from Conjugated Polyphenylenebenzobisoxazole

通过光谱技术、电化学特性等对聚苯撑苯并双噁唑(PBO)的性能进行了系统研究。通过电化学分析获得该聚合物最高占有分子轨道能级(HOMO)大约为EHOMO=5.69eV,通过光谱分析计算得到最低空轨道能级(LUMO)大约为ELUMO=2.99eV。PBO的溶液光致发光在430～500nm范围,呈现明显的浓度效应;其薄膜的光致发光峰大约位于500nm。研究制作了以PBO为发光层的单层电致发光器件ITO/PBO(60nm)/Al和双层电致发光器件ITO/CuPc(25nm)/PBO(60nm)/Al,其电致发光峰位具有聚集态发光的特征。器件的发光亮度和稳定性在双层器件中获得提高,器件的发光峰位随驱动电压大小在520～555nm范围变化。

Photophysical, electrochemical and optoelectronic properties of a conjugated polymer, poly （p- phenylene benzobisoxazole） （PBO） were investigated. Due to its delocalized π electrons in chemical structure, the material is low in solubility, excellent in thermo-oxidative stabilities and mechanical properties; it becomes increasingly important in many applications. This work focused on the photophysical properties, in particular the luminescence property of PBO and its preliminary light emitting device fabrication. The properties of the material were investigated using absorption, and luminescence spectrometries, cyclic voltammetry. Photoluminescence from PBO solution were in the range of 430 - 500 nm. Concentration dependence was observed. Photoluminescence of the film peaked at 500 nm. It was indicated that the emission shift from solutions is due to the intermolecular interaction. Through electrochemical analysis of the polymer the highest-level occupied molecular orbital （HOMO） is about EHOMO = 5.69 eV, through spectral analysis the lowest unoccupied molecular orbital energy （LUMO） is about ELUMO = 2.99 eV. Single-layer and double-layer light emitting devices were prepared, which have structures as follows ： （a） ITO/PBO（60 nm）/Al for the single-layer device, and （b）ITO/CuPc（25 nm）/PBO（60 nm）/Al double-layer device. Their current-voltage characteristics were analyzed and compared. Although CuPc absorbed in visible, it showed a transmitted window around green spectral range. This allows the light from the device through as it emitted in green around 520 nm. Brightness and stability were much improved in double-layer devices. However a voltage-dependent colour change was observed for the double-layer device. The electroluminescence intensity is increased as the voltage increase, which reaches a maximum at 21 V. The red shift is observed in the emission spectra as the driving voltage increased. It is predicted that this may be related to excitation state of PBO at the different field strength, which requires further investigation in the future.