【作者】 师全民；

【导师】 侯延冰；

【作者基本信息】 北京交通大学 ， 光学， 2009， 博士

【摘要】 本论文研究了共轭聚合物MEH-PPV及其掺杂体系中的激子离化和载流子输运特性。激子离化部分主要研究了二氧化钛纳米管掺杂在聚合物光伏器件中的作用和激子在聚合物/金属电极界面离化的现象。载流子输运部分首先介绍了垂直电场下制备聚合物薄膜对载流子迁移率的影响,然后是聚合物中掺杂富勒烯以及高温处理对于双极性载流子输运的影响。本论文在以下几个方面有所创新:1.利用瞬态光伏的方法研究了ITO/MEH-PPV/Al器件的性能。使用500nm光照时出现负-正交替的光伏信号,但吸收边附近的脉冲光照射下负光伏信号消失。采用在不同波长脉冲光照下载流子在薄膜中的分布模型分析了该现象并证实了在ITO/MEH-PPV界面激子通过向ITO电极转移电子实现激子离化。木工作的创新在于利用激子分布模型引入了将电极界面离化率量化的方法。2.使用飞行时间和光致发光电场猝灭的方法研究了MEH-PPV:TiO₂纳米管薄膜的载流子输运和激子离化性能。许多文献报道了聚合物掺杂二氧化钛纳米颗粒可以很大程度提高光伏器件的效率,但掺杂二氧化钛如何提高光伏效率的物理机制尚不得而知。本实验研究证明聚合物中掺杂TiO₂纳米颗粒并不能改善薄膜中载流子的输运特性,但电场下光致发光猝灭的实验结果表明激子在MEH-PPV和TiO₂纳米管界面上可以发生电荷转移使得电场下激子离化变得容易。3.载流子迁移率较低一直是影响聚合物光电产业发展的一个重要障碍。本论文一个突出的创新点在于利用垂直静电场制备了具有高迁移率的MEH-PPV薄膜。飞行时间实验表明电场下制备的薄膜与无电场条件下制备的薄膜相比其载流子迁移率提高了3-4倍。小角X射线研究表明电场下制备薄膜可以有效增加有机薄膜的有序性,从而改善了载流子的输运特性。4.研究了MEH-PPV:C₆₀体系的双载流子输运性能。研究发现在MEH-PPV中原本无法测量的电子迁移率在较低C₆₀掺杂浓度时可以用飞行时间方法测量并且电子迁移率随C₆₀掺杂浓度而迅速增大,这表明掺杂C₆₀不仅能有效的转移电子还能够形成电子输运网络将电子输运到相应电极。该实验表明在聚合物中分散的C₆₀分子或C₆₀晶粒可以为电子的输运提供输运通道,而且输运网络在较低掺杂浓度（5wt-%～10wt-%）时就可以形成。5.研究了高温处理对MEH-PPV:C₆₀掺杂体系中双载流子输运性能的影响。结果表明因为高温处理后能量无序和位置无序都有很大程度的提高（分别从0.097eV变为0.132eV,从2.2变为4.47）导致了空穴迁移率减小。电子迁移率在退火后低于测量范围,扫描电镜的结果发现高温下C₆₀发生聚集并有向上表面移动的趋势从而导致了电子输运网络的中断。原子力显微镜的结果表明高温处理后表面的起伏变大,导致了高温处理后同类材料相同面积的光伏器件中有机材料和金属电极（Al）的有效接触面积变大从而有利于激子在界面的离化和电荷的收集。更多还原

【Abstract】 The exciton dissociation and carrier transport properties of pristine as well as doped random polymer have been investigated.1 Transient photovoltage（TPV） is investigated for the sandwich device of ITO/ MEH-PPV（500nm）/Al.A negative TPV signal appears followed by a positive one when using pulse laser wavelength of 500nm.Using exciton distribution model under pulse laser with different wavelength,the exciton dissociation at ITO/ MEH-PPV interface by transfer an electron into ITO electrode is demonstrated which result in the negative TPV signal.2 The performance of TiO₂ nanotubes in bulk heterojunction of MEH-PPV:TiO₂ nanotubes is investigated.The time-of-flight result shows that the transport properties of both hole and electron are not improved.However,photoluminescence under the influence of the electric field indicates that the dissociation of excitons in the MEH-PPV:TiO₂ composite only requires a smaller electric field.It can be attributed to the facility of exciton dissociation at TiO₂ interface by transferring an electron into TiO₂.3 The MEH-PPV film is prepared under the presence of a DC electric field.The time-of-flight hole mobility enhances evidently compared with the as-prepared film. Small-angle X-ray diffraction data show that the disorder of the film prepared under electric field decreases.4 Ambipolar charge transport in bulk heterojunction of MEH-PPV:C₆₀ composite are investigated.Electron mobility is below the measurable range in pristine film. However,electron mobility can be measured when the weight ratio of C₆₀:MEH-PPV increased to 1:18.Moreover,it increases two orders of magnitude when the weight ratio of C₆₀:MEH-PPV increased to1:3.This work demonstrates that the dopant C₆₀ can form electron transport network in MEH-PPV:C₆₀ composite.5 The effects of thermal annealing treatment on carrier transport and film morphology are investigated for MEH-PPV:C₆₀ system.By analysing the temperature dependence of field dependent mobility in Gaussian disorder model（GDM）,the drop of hole mobility can be attributed to the large value of both positional disorder and energetic disorder,which are 4.47 and 0.132eV,respectively.Electron mobility is below the measurable range as long as the devices experience thermal treatment.According to SEM study,the drop of electron mobility results from the discontinuity of the electron transport path due to C₆₀ aggregation and vertical segregation.The AFM result shows that thermal annealed treatment increases the roughness of the surface and enhances the virtual interface with electrode,which facilitates exciton dissociation and carrier collection for photovoltaic devices.更多还原