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基于噻吩[3,4-b]并噻吩的聚合物给体材料的设计及光伏性能研究
朱党强
导师阳仁强
2015-11
学位授予单位中国科学院研究生院
学位授予地点北京
学位专业化学工程
关键词聚合物太阳能电池 给体材料 Homo能级调控 噻吩[3 4-b]并噻吩
摘要聚合物太阳能电池由于具有质轻、成本低、结构多样化、可调控性能佳、制备工艺简单、可通过溶液加工处理制备柔性器件等显著优点而备受关注。在现行的电池器件结构中,活性层中高性能给体材料的设计合成是有机太阳能电池研究的一个重要方面。 目前,基于噻吩[3,4-b]噻吩的窄带隙聚合物给体材料获得了巨大成功,其光电转换效率已突破了10%,但是相对较低的开路电压限制了其光电转换效率的进一步提高,因此,本论文的主要研究工作围绕基于噻吩[3,4-b]噻吩的聚合物给体材料而展开,通过调节侧链取代基以及主骨架引入π桥来降低聚合物的HOMO能级,进而提高聚合物电池开路电压,达到改善光电转换效率的目的。 第二章与第三章中,通过将不同缺电子芳杂环(1,2,4-噁二唑,1,3,4-噁二唑,噻唑)替换噻吩[3,4-b]并噻吩2位的常用取代基酯基,羰基等构建了新的受体单元,并进一步通过Stille偶联反应与常用给体单元苯并二噻吩进行共聚。结果表明,由于不同杂环的吸电子能力有所差别,其HOMO能级也各不相同。其中,1,2,4-噁二唑5位取代PBDT-iTTO5具有最深的HOMO能级,当取代位置为3位时,聚合物PBDT-iTTO3的HOMO能级最高。而电池器件的开路电压也从0.43到0.68 V变化浮动。在此基础上,选用1,3,4-噁二唑取代噻吩[3,4-b]噻吩的受体单元进行了深入研究,通过改变烷基侧链大小以及共聚给体单元,设计合成了聚合物PBDT-TTSO。该材料具有较深的HOMO能级(-5.32 eV)以及具有与含氟取代聚合物PTB7-Th相媲美的开路电压(0.78 V),光电转换效率可达5.86%(VOC = 0.74 V, JSC = 13.1 mA/cm2, FF = 60.5%)。除此之外,针对硫醚化合物中的硫原子极易被氧化的性质,通过不同氧化剂对该聚合物进行处理,巧妙地采用了从单体到聚合物氧化的“类比”的研究方法来证实了其可能的反应位点为硫醚结构中的硫原子。有趣的是,相对PBDT-TTSO而言,氧化产物的光电转换效率仍然保持70%以上。本研究工作的意义在于首次提出利用缺电子芳香杂环有效地调控聚合物的HOMO能级的策略以及证实了硫醚化合物中硫原子的易氧化特性,对以后的分子设计有着重要的指导作用。 第四章中,通过将噻吩[3,4-b]并噻吩的侧链取代基替换为硫酯单元,解决了上述硫醚结构的硫原子极易被氧化的缺点,进而设计合成了两个聚合物PBDTT-TTSO和PBDTT-TTSE。结果表明,新合成的聚合物的吸收光谱发生明显的红移,光学带隙在1.5 eV左右,同时HOMO能级有所降低。在常规的器件结构中,基于聚合物 PBDTT-TTSE的最优电池器件的光电转换效率到达5.80%(VOC = 0.70 V,JSC = 14.6 mA/cm2,FF = 56.7%)。 第五章中,成功地设计并合成了以噻唑作为π桥的基于噻吩[3,4-b]并噻吩的直线型主骨架聚合物PTBTz-2和PTBTz-5。结果表明,两种聚合物在HOMO能级大大降低的同时,带隙明显变大。相对于聚合物PTBTz-5,聚合物PTBTz-2表现出更低的HOMO能级,更平面的分子结构。同时该材料与富勒烯受体的共混材料表现出更好的形貌与相分离,从而获得了16.8 mA/cm2的短路电流以及9.53%的高光电转换效率。 除了研究基于噻吩[3,4-b]噻吩体系之外,在第六章中,设计合成了基于不同长度的烷氧侧链取代噻吩并吡咯二酮(TPD)的聚合物PBT-Os。由于共轭效应的阻断,烷氧侧链对聚合物材料的吸收光谱及HOMO能级几乎没有影响,所制备的光伏器件的开路电压均能保持0.92 V以上,此外,利用了O原子半径小的优点,降低了主骨架与侧链的空间位阻,这有利于聚合物中TPD单元更能接近富勒烯受体。由于理想的相分离和表面形貌,聚合物PBT-O8的短路电流高达14.3 mA/cm2,使得其光电转换效率可达8.22%。随着直线侧链长度的增加,其短路电流密度明显下降,使得光电效率线性下降。本研究工作首次报道了通过烷氧侧链取代非共轭体系来提高光电性能的策略,同时,该类材料有望作为宽带隙材料在叠层太阳能电池中有着广泛的应用前景。
其他摘要Polymer solar cells (PSCs) have attracted much attention due to their advantages of easy fabrication, simple device structure, low cost, light weight, and the capability to be fabricated into flexible devices via solution processing. Accoding to the current device structure, the design and syntheise of high performance photovoltaic polymers are the crucial issue for PSCs. So far, thieno[3,4-b]thiophene(TT)-based low band-gap polymers have achieved great success with high power conversion efficiency (PCE) of over 10%. However, the TT-based polymers usually exhibit relatively low open circuit voltage (VOC), which confines the power conversion efficiency. In this dissertation, we designed and synthesized novel TT-based polymers to obtain deep HOMO energy level, through the fine tuning by the different substituted groups and the introduction of π bridge, which will regulate the VOC in PSCs feasibly. In the chapter 2 and 3, it was firstly reported a series of electron-deficient aromatic heterocycle applied to TT-based polymer to tune the HOMO energy level. According to the result, the HOMO energy levels could be asjusted feasibly due to the various electron-withdrawing effect of the heterocycle. Among them, when the substituent was position 5 of the 1,2,4-oxadiazole, the corresponding polymer exhibits the deepest HOMO energy levels. In contrast, when the substituent was changed to 3-position, the HOMO energy level have a sharp increase. When fabricated into PSCs, the VOC of the polymers rangs from 0.43 to 0.68V. Then based on the above work, The polymer PBDT-TTSO based on 1,3,4-oxadiazole as the substituent was further investaged throng the change of the side chain and the donor unit, which exhibits a deep lying HOMO energy level of -5.32 eV and PCE of 5.86% with a relative high VOC of 0.74 V. Furthermore, the stability of the polymer was preliminarily investigated through dealing with different oxidants. The results indicate that the S atom of thioether is the most possible reaction site and the polymer PBDT-TTSO can still remain relative high photovoltaic performance after oxidized by strong oxidants. This work demonstrates a new method to tune HOMO levels of TT-based polymers through introducing electron-deficient aromatic heterocyclic moiety. In the chapter 4, we replaced the alkyl chain of ketone-substituted thieno[3, 4-b] thiophene with alkylthio side chain to develop a new acceptor thioester-based acceptor (TTS). Then, two new polymers PBDTT-TTSO and PBDTT-TTSE were designed and synthesized by Stille coupling reaction. The TTS acceptor moieties made the two polymers exhibit a lower band gap (~1.5 eV) and desirable HOMO and LUMO energy levels relative to the fullerene acceptors for PSCs. The PBDTT-TTSE-based photovoltaic device demonstrates a VOC of 0.70 V, a JSC of 14.6 mA cm-2, a FF of 56.7%, and a high PCE of 5.80%. This study indicates that thioester substituted thieno[3, 4-b] thiophene may be a highly useful building block for further design of high performance photovoltaic polymers. In the chapter 5, we successfully introduced thiazole unit into the backbone of TT-based polymers as the π bridge and synthesized two polymers PTBTz-2 and PTBTz-5 due to the different coupling positions between TT unit and thiazole unit (2 or 5-position). The results exhibited the optical bandgap of these two poymers obviously increased with the HOMO energy levels greatly reduced. In comparison with PTBTz-5, PTBTz-2 demonstrated deeper HOMO energy level, more planar molecular structure and higher performance photovoltaic. Due to the excellent phase separation and surface morphology, a remarked JSC of up to 16.8 mA/cm2 and high PCEs of 9.53% for PTBTz-2 were obtained. Apart from the above PBDTTT system, we also modified PBDTTPD system to investigate the effect of the alkoxyl side chains substituting on the non-conjugated system. The PBT-Os derivatives with various lengths of alkoxyl side chains were successfully synthesized. The experimental results have shown that the alkoxyl side chain almost has a negligible impact on the HOMO energy level and the optical absorption, and thus the PBT-Os polymers still maintained a high VOC >0.92 V in standard BHJ solar cells. More interestingly, the insertion of smaller size O atom reduces the steric hindrance of the side chain and makes the corresponding polymers more sterically accessible to the fullerene acceptor. As a result, due to the excellent phase separation and surface morphology, a remarked JSC of up to 14.3 mA/cm2 and high PCEs of 8.22% for PBT-O8 were obtained. To our knowledge, it is firstly reported that the method to improve the performance through alkoxyl side chains substituting on the non-conjugated system, and the PBT-Os analogues are promising systems for use in the wide band-gap cell of tandem solar cells.
作者部门先进有机功能材料团队
学科领域有机光电材料
公开日期2016-06-30
学位类型博士 ; 学位论文
语种中文
文献类型学位论文
条目标识符http://ir.qibebt.ac.cn/handle/337004/8088
专题先进有机功能材料研究组
作者单位中国科学院青岛生物能源与过程研究所
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朱党强. 基于噻吩[3,4-b]并噻吩的聚合物给体材料的设计及光伏性能研究[D]. 北京. 中国科学院研究生院,2015.
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