Benzodithiophene and Imide-Based Copolymers for Photovoltaic Applications
Benzodithiophene and Imide-Based Copolymers for Photovoltaic Applications
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DOI：
10.1021/cm2038427
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发表时间：
2012-04-10
影响因子：
8.6
通讯作者：
Olson, Dana C.
中科院分区：
文献类型：
--
作者：
Braunecker, Wade A.;Owczarczyk, Zbyslaw R.;Olson, Dana C.
设计了一种用于有机光伏(OPV)的低光学带隙的共轭交替共聚物。与硫代吡咯二酮(TPD)和苯并二硫杂环戊二烯(BDT)的共聚物相比，TID和BDT的共聚物具有更低的禁带宽度(接近0.4 eV)。除了分子内电荷转移稳定(即“推-拉”效应)，前者的共聚物的奎宁共振结构是通过异吲哚单元中芳香共振能量的增加而稳定的。此外，通过对BDT单体进行化学修饰，可以调节共聚物的HOMO水平，从而在光伏器件中实现大于1V的开路电压。尽管具有优化的带隙，但与TPD类似物相比，含TID的聚合物表现出更低的光电导(时间分辨微波电导)，并降低了器件效率(2.1%比4.8%)。这些结果部分归因于形态结构，计算模型表明TID共聚物具有扭曲的主链，X射线衍射数据表明聚合物薄膜没有形成有序结构域，而TPD共聚物则更平坦，形成了偏序结构域。
Conjugated alternating copolymers were designed with low optical band gaps for organic photovoltaic (OPV) applications by considering quinoid resonance stabilization. Copolymers of thienoisoindoledione (TID) and benzodithiophene (BDT) had appreciably lower band gaps (by similar to 0.4 eV) than copolymers of thienopyrroledione (TPD) and BDT. In addition to intramolecular charge transfer stabilization (i.e., the "push-pull" effect), the former copolymer's quinoid resonance structure is stabilized by a gain in aromatic resonance energy in the isoindole unit. Additionally, the HOMO levels of the copolymers could be tuned with chemical modifications to the BDT monomer, resulting in open circuit voltages of greater than 1 V in photovoltaic devices. Despite the optimized band gap, TID containing polymers displayed lower photoconductance, as determined by time-resolved microwave conductivity, and decreased device efficiency (2.1% vs 4.8%) as compared with TPD analogues. These results were partially attributed to morphology, as computational modeling suggests TID copolymers have a twisted backbone, and X-ray diffraction data indicate the polymer films do not form ordered domains, whereas TPD copolymers are considerably more planar and are shown to form partially ordered domains.