【作者】 胡子阳；

【导师】 张建军；

【作者基本信息】 南开大学 ， 微电子学与固体电子学， 2012， 博士

【摘要】 有机聚合物太阳电池具有重量轻、成本低、与湿法成膜的大面积制备技术相兼容以及可制成柔性、特殊形状器件等优点。通过设计和合成新型聚合物半导体材料，可以很容易地实现对器件光伏性能的调控。基于上述这些独特的优点，聚合物太阳电池受到了国内外研究小组的广泛关注，成为近年来太阳能电池技术最热门的研究领域之一。目前文献报道的小面积聚合物太阳电池的能量转化效率（PCE）已超过10%，达到了商业化生产的要求，聚合物太阳电池也因此最有希望成为下一代商业化的太阳能电池产品之一。目前聚合物太阳电池的研究主要集中在多功能新型聚合物材料的开发和对器件结构设计、性能的优化等方面。本论文针对目前聚合物太阳电池存在的问题，把握聚合物电池的重点研究方向，依托本实验室的研究基础，以器件的性能优化为切入点展开对聚合物电池的研究，从两个方面对聚合物太阳电池进行了分步优化：一是电池体相异质结活性层的优化，二是活性层与电极之间界面的修饰和优化。在优化活性层特性的基础上，进行活性层与电极之间界面的修饰和优化，期望达到电池性能优化效果的叠加。本论文的主要研究内容和成果如下：第一，在室温范围、空气中、无热退火的条件下，制备了基于P3HT:PCBM活性层体系的高性能聚合物太阳电池。研究了旋涂转速、旋涂时间和室内温度三者对活性层溶剂挥发速率的影响。研究发现通过调节室温、旋涂的转速和时间可以控制活性层溶剂挥发的速率，从而实现活性层材料的自组装功能。活性层自组装功能的实现，使得P3HT的有序结晶度提高，空穴载流子迁移率提升，从而平衡了活性层中载流子的传输，改善了电池的填充因子（FF）和短路电流密度（Jsc）。在室温、空气中、无热退火的条件下，优化的基于P3HT:PCBM的电池效率达到4.71%，接近国际报道水平（4-5%）。由于此电池制备条件不需要加热退火，与柔性衬底相兼容，基于此工艺制备的柔性聚合物电池的效率达到4.00%。由于在室温范围内可以控制溶剂挥发速率，实现活性层的自组装功能，采用与卷对卷（roll to roll）兼容的浸渍涂布（dip coating）的工艺，亦实现了高性能聚合物电池的制备。第二，在优化电池活性层的基础上，分别选取了不同的TCOs（FTO、IWO、AZO等）作为电极材料应用到聚合物电池中，通过电极与活性层之间的界面修饰和优化，实验结果表明这些TCOs完全可以取代ITO，而不会降低器件的性能。通过实验详细分析了TCO的电学、光学特性、表面形貌和功函数对电池性能参数的影响，结果显示TCO的电学特性和表面形貌对电池的FF和Jsc有一定的影响，而电池的Voc与选择使用的TCO电极种类影响很小。这些研究成果表明在降低电池成本的同时还为电池的电极选择提供了更大的灵活性。第三，在研究了电极材料对聚合物电池性能参数影响的基础上，借鉴无机硅基薄膜电池陷光结构的理念，将具有陷光作用的绒面电极取代平面电极应用到聚合物电池中，增强了聚合物电池对太阳光谱的吸收和利用。通过绒面电极表面处理和结构优化，获得了良好的绒面电极与活性层的界面接触，保证了在提升电池Jsc的同时不牺牲电池的FF和Voc。与平面电极电池相比，绒面电极电池的Js增加了10%，PCE提升了8%。研究还发现采用“U”型表面形貌的绒面电极比“V”型绒面电极更能获得良好的聚合物电池性能。电池的反射光谱和外量子效率测试均表明，绒面陷光电极能显著提高电池在陷光波段的吸收和利用效率。第四，由于电极修饰层的特性对聚合物电池的性能起着至关重要的作用，研究了PEDOT:PSS掺杂不同浓度的乙二醇（EG）和二甲基亚砜（DMSO）对PEDOT:PSS薄膜光电特性和形貌的影响，以及掺杂改性后的PEDOT:PSS薄膜作为电池的修饰层对聚合物太阳电池性能的影响。实验结果表明：PEDOT:PSS中掺入溶剂EG和DMSO均能提高薄膜的电导率，当掺杂浓度为10wt%时，薄膜的电导率比未掺杂时分别提高了约2个和3个数量级。EG和DMSO掺杂PEDOT:PSS后，薄膜的透过率几乎没有发生变化，但薄膜的表面粗糙度增加。将掺杂后的PEDOT:PSS薄膜作为修饰层应用到聚合物电池中，发现高电导率的PEDOT:PSS降低了器件的串联电阻（Rs），增加了器件的Jsc，但掺杂后的PEDOT:PSS薄膜粗糙度的增加也影响到了电池的FF。实验结果显示：当PEDOT:PSS掺杂EG和DMSO的浓度为10wt%时，器件的Rs最小，PCE分别达到4.34%和4.45%，器件效率比未掺杂时分别提高了29%和30%。第五，选择了ZnO作为电极界面修饰层，制备了反型结构的聚合物太阳电池，避免了由于使用具有腐蚀性和亲水性的PEDOT:PSS带来的器件性能的衰退，提高了聚合物电池的稳定性。利用水浴法制备了ZnO纳米柱阵列，并研究了不同ZnO纳米形貌作为界面修饰层对反型结构电池性能的影响。研究发现稀疏ZnO纳米柱阵列有利于电子的收集和传输，能显著提高电池的性能。利用金属有机化学气相沉积法（MOCVD）制备了厚度系列和掺杂系列ZnO薄膜，研究了不同厚度和不同导电性ZnO薄膜作为界面修饰层对电池性能的影响。实验发现ZnO薄膜在一定厚度下，适当提高其电导性可以改善电池的性能。与普通结构的电池相比，利用ZnO作为界面修饰层制备的反型结构电池，器件的稳定性显著提高。更多还原

【Abstract】 Polymer solar cells (PSCs) with light-weight, compatible with low-cost andlarge-area of wet-film manufacturing technology, and can be made flexible, specialshape of the device. Furthermore, through molecular design and synthesis of novelsemiconductor, device performance can be easily improved. Based on these aboveunique advantages, PSCs have been attracted much attentions of the research teamsat home and abroad, and have thus become one of the most popular fields of study.Nowadays, power conversion efficiency (PCE) over10%of PSC with a smallarea has been reported in the literature, achieving the requirements of thecommercial production, has thus become one of the most promising next-generationsolar cell products. So far, research on PSC is mainly concentrated in thedevelopment of versatile new polymer materials, structure design, and deviceperformance optimization. In this thesis, based on our laboratory conditions, weaddress to optimize the device performance in order to solve the existed problems ofPSCs and grasp the research direction of PSCs. The optimization of PSCs wasperformed by a step-by-step process. The first process is to optimize the bulkheterojunction active layer of PSCs; the second process is to optimize the interfacebetween the active layer and the electrode. The first step is the foundation of thesecond step, which expects to achieve the perfect optimization of the deviceperformance. Our research will offer the effective way to further enhance theperformance of PSCs in the future. The main contents and results of this thesis are asfollows:First, high performance and free-thermal annealing PSCs were fabricated basedon P3HT:PCBM active layer at room temperature in air conditions. Throughadjusting the speed and time of the spin-coating process, and room temperatureduring the solvent evaporation of the active layer, the rate of solvent evaporation wascontrolled, and the self-assembly function of the active layer material can beachieved. Self-assembly function of the active layer makes the ordered degree of crystallinity of P3HT and improved the hole carrier mobility, which balances thecarrier transport in the anctive layer. This improved the fill factor (FF) andshort-circuit current density (Jsc) of PSCs. The optimization of P3HT:PCBM deviceperformance is close to the international reported level (4-5%), and its specificparameters were as follows: open circuit voltage (Voc)=0.61V, FF=0.71, Jsc=10.87mA/cm2and PCE=4.71%. Since this process does not require heating annealing, theefficiency of flexible PSCs achieved4.06%. In view of the adjusted solventevaporation rate by room temperature, high-efficiency PSCs were also fabricatedusing dip coating process which is compatible with roll to roll technique.Second, the current expensive ITO was replaced by alternative transparentconductive film (TCO), the aim is to reduce the device cost and provide moreflexibility to the choice of electrodes. A series of different TCOs (FTO, IWO, AZO,etc.) as the electrode material is applied in PSCs. The results demonstrated that theTCOs can completely replace the ITO and does not reduce the device performancethrough modification and optimization of the interface between the electrode and theactive layer. The influence of electrical, optical properties, surface morphology andwork function of different TCOs on device performance parameters was analyzed. Itwas found that the electrical properties and surface morphology of TCO have acertain impact on the device FF and Jsc, while the device Vocis independent of thechoice of electrodes.Third, the textured electrode with the light-trapping effect was introduced intoPSCs, which replaces the planar electrodes in PSCs in order to strengthen theabsorption of the solar spectrum. The excellent interface contact between theelectrode and the active layer was achieved by rational optimization of the texturedelectrode surface, which ensures the increased Jscand keeps the device FF and Voc.Compared with the planar electrode cell, Jscand PCE of the textured cell enhancedby10%and8%, respectively. The study also showed that the "U" shaped texturedelectrode is more suitable than the "V" shaped textured electrode for application inPSCs. The tests of the reflection spectra and external quantum efficiency (EQE) ofPSCs demonstrate that the light-trapping electrode could significantly increase thelight absorption and utilization. Fourth, after PEDOT:PSS doped with different concentrations of EG andDMSO, the conductivity, transmittance and morphology of doped PEDOT: PSS filmwere investigated. The influence of the doped PEDOT:PSS film as the anodemodification layer on the device performance of PSCs was researched. When thedoping concentration of EG and DMSO was10wt%, the electrical conductivities ofthe film were increased about two and three orders of magnitude, respectively,compared with the undoped. The transmittance of the EG and DMSO-dopedPEDOT:PSS did not change, but the film surface roughness was increased. Theenhanced conductivity of the doped PEDOT:PSS film reduced the device seriesresistance (Rs), resulting in increased the device Jsc, but the doped PEDOT:PSS filmwith increased roughness also affected the device FF. The experimental resultsshowed that when the doping concentration of EG was10wt%, the device with thelowest Rsshowed a PCE of4.34%which enhacend by29%than the undoped. Whenthe doping concentration DMSO was10wt%, the device with the lowest Rsshoweda PCE of4.45%which enhacend by30%than the undoped.Fifth, the inverted structure of PSCs was fabricated by selecting the modifiedlayer of ZnO to optimize the electrode interface, which avoids the use of corrosiveand hydrophilic PEDOT:PSS resulting in the recession of the device performance.The ZnO nanorods arrays were prepared by water bath, and were applied in invertedPSCs. The impact of the different ZnO nano-morphology as the interfacemodification layer on the device performance was investigated. The study found thatthe sparse ZnO nano-pillar array was helpful for electronic collection and transport,thereforce, can significantly improve the device performance. Thickness series anddoping series of ZnO thin films were prepared by metal organic chemical vapormethod (MOCVD), and were applied in PSCs as the interface modification layer. Itwas found that an appropriate increase in the ZnO conductivity can improve thedevice performance at a fixed ZnO film thickness. Compared with the generalstructure, the stability of the inverted device useing ZnO as an interface modificationlayer significantly inproved.更多还原