【作者】 刘博；

【导师】 陆丹；

【作者基本信息】 吉林大学 ， 高分子化学与物理， 2016， 博士

【摘要】 共轭聚合物材料具有质轻、廉价、易加工等特点,在半导体光电器件制备方面应用前景广阔。然而,与无机半导体材料相比,有机半导体材料的缺点是电荷输运能力较差,表现为迁移率较低。目前使用聚合物半导体材料制备的电子器件还未达到商品化的门槛。应用复杂体系电荷转移理论来描述有机/聚合物体系的电荷输运过程,通过结合激子扩散、载流子复合、电极—半导体接触条件等模块,我们构建出了有机/聚合物太阳能电池(及场效应晶体管)全器件模型。应用全器件模型进行理论与模拟研究,可以方便地建立起微观物理过程与器件宏观性能之间的联系。进而有助于理解器件性能限制因素的本源,并为实验提供改进方向。与目前更流行的、同样包含唯象参数的动力学蒙特卡洛方法全器件模型相比,我们构建的主方程方法全器件模型的最大优势是数值求解容易且快速。对聚合物给—受体二元共混型本体异质结太阳能电池体系进行模拟,光生激子的扩散与分离以及自由载流子在同相内和异相间的输运是核心步骤。在有机/聚合物本体异质结太阳能电池全器件模型合理性验证研究方面——我们发现迁移率与能量无序度间存在非阿瑞尼乌斯二次方关系;通过模拟退火过程,发现活性层相分离程度对器件效率影响很大,存在所谓的“最佳形貌”;迁移率与器件效率间的关系存在争议,我们发现随迁移增加器件效率提高并最终趋于饱和;通过模拟还发现,当电子和空穴迁移率不平衡、电极—活性层接触势垒较高且不平衡时,会导致局部电荷积累,进而导致双分子复合增强。通过将唯象参数引入全器件模型,使得电荷从电极注入及电荷被电极抽取不再是简单的反向过程,从而实现了对注入暗电流和抽取光电流的精确模拟。我们发现对电极—活性层能带进行匹配,可以降低接触势垒,显著提高器件效率;较高的接触势垒导致内量子效率降低的本源是局部空间电荷堆积致使双分子复合损失增多;另外,接触势垒高度对双分子复合速率影响较大,对成对复合速率影响较小。在对铁电聚合物材料界面层—本体异质结太阳能电池体系模拟研究方面:通过对已报道的存在争议的实验结果进行精确模拟,我们解释了一类聚合物铁电材料作为电极修饰界面层的作用机理,指出“电极优化与能带匹配”机理是合理的,而铁电薄膜极化引入“永久额外内电场和串联电阻”这一机理存在漏洞。结构上包含三个电极的有机场效应晶体管是注入型电荷传输器件,针对其的主方程方法全器件模型构建可以看作是对已有的有机/聚合物太阳能电池模型去除光物理过程模块的简化。目前,利用我们构建的有机场效应晶体管全器件模型模拟,可以得到输出曲线、载流子沿器件厚度一维分布、能量无序度与迁移率关系等结果。更多还原

【Abstract】 Conjugated polymer materials with the merits of light weight, cheap, convenient fabrication, have brilliant prospect in application. Comparing with inorganic semiconducting materials, organic semiconducting materials show poor charge transport ability,to be specific, the mobility is still too low. To date, the devices using polymer materials are still at an early stage of commercialization.In this thesis, we will show how to develop full device models of organic/polymer solar cells and organic field-effect transistors by adopting mesoscopic Pauli master equation method with disorder matter system charge transport theories and proper descriptions of exciton diffusion, charge carriers recombination, metal-semiconductor contact condition, etc. Full device model simulation skills make it possible to connect microscopic physics process with macroscopic device performance, which is helpful for understanding the origins of limitations and provide directions of further improvement. Comparing with other full device models, to be specific, the dynamic Monte Carlo models which also include many phenomenological parameters, our model is more efficient.For the polymer bulk heterojunction(BHJ) solar cells, photogenerated exciton diffusion and separation, free charge carriers transport and recombination are key steps.In the stage of polymer BHJ solar cells full device model testing, we found that: There exists non-Arrhenius correlation of mobility and energy disorder; By introducing annealing simulation, it’s found that there exists an optimum morphology which is the result of trade-off between exciton separation surfaces and charge transport channels;The relation between mobility and cell performance is still a controversial issue. We found that with the increase of mobility, device efficiency will increase gradually and finally level off; It’s also found that local charge accumulation caused by unbalance of electron and hole mobilities or the electrode contact barrier heights at both electrodes can lead to significant efficiency loss. The origin of such loss is due to enhanced charge carrier recombination.For the purpose of properly dealing with charge injection from the electrode and extraction into the electrode, we introduced phenomenological parameters about contact conditions, as a result the injected dark current and extracted photocurrent can be simulated and fitted with experimental data. It’s found that optimized level tuning can significantly improve the device efficiency; And the origin of higher contact barriers resulting in reduced internal quantum efficiency is the enhanced bimolecular recombination rate caused by local space charge accumulation; In addition, the correlation between contact barrier height and bimolecular recombination rate is robust, but it gets less stronger when extended to geminate recombination rate. In the work of studying the mechanism of polymer ferroelectric material as the interfacial layer in polymer BHJ solar cells, we argue that the electrode improvement and energy level alignment mechanism is reasonable, whereas the mechanism of polarized layer introducing both permanent additional internal electric field and series resistance is not that complete.Organic field effect transistors are injection-type charge transfer device which have three electrodes. The full device model of organic field effect transistors can be regarded as a simplified version of our already built solar cells model. For now, the application of this model includes simulating the output characteristics, the charge carrier distribution along the device thickness direction, the correlation between energy disorder and mobility, etc, while the corresponding results are proved to be credible.更多还原