Influence of the -CN substitution position on the performance of dicyanodistyrylbenzene-based polymer solar cells
Influence of the -CN substitution position on the performance of dicyanodistyrylbenzene-based polymer solar cells
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DOI：
10.1039/c9py01781j
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发表时间：
2020-03-07
影响因子：
4.6
通讯作者：
Cao, Yong
中科院分区：
文献类型：
--
作者：
He, Baitian;Yin, Qingwu;Cao, Yong
聚合物给体的分子工程是提高聚合物太阳能电池光电性能的必要条件。本文报道了-CN基团在二氰二苯基苯（DCB）基团基共聚物中的取代位置极大地影响了PSCs的分子填充和光伏性能。以DCB为电子给体，5,6-二氟苯并[c][1,2,5]噻二唑（DFBT）或萘[1,2-c:5,6-c ']双[1,2,5]噻二唑（NT）为电子受体，设计并合成了四种新型共聚物，研究了改变-CN取代位置的影响。密度泛函理论（DFT）计算表明，具有外取代位置的p -o衍生物共聚物比具有内取代位置的p -i衍生物共聚物具有更多的平面共轭主链，从而提高了吸收系数并提供了更高的电荷迁移率。此外，二维（2D）掠射广角x射线散射（GIWAXS）图清楚地表明，p -o导数共混物表现出强烈的面对pi-pi叠加。这种有序的聚合物填料促进了电荷在垂直方向上的传输。相比之下，p -i衍生物的共混物倾向于边缘上的层状堆积。将每个共聚物与小分子受体（tic - 4f）结合，p -o衍生物共混器件的最佳功率转换效率（PCE）为10%，而基于p -i衍生物共聚物的器件的PCE仅为6.67%。我们的比较研究表明，改变官能团取代位置会影响分子的排列和分子性质。这种方法为高性能psc材料的分子设计提供了一条途径。
Molecular engineering of polymer donors is imperative to improve the photovoltaic performance of polymer solar cells (PSCs). Here, we report that the substitution position of the -CN group in dicyanodistyrylbenzene (DCB) moiety-based copolymers greatly affected the molecular packing and photovoltaic performance of PSCs. Four novel copolymers based on DCB units as electron donors and 5,6-difluorobenzo[c][1,2,5]thiadiazole (DFBT) or naphtho[1,2-c:5,6-c ']bis[1,2,5]thiadiazole (NT) units as electron acceptors were designed and synthesized to investigate the effects of altering the -CN substitution position. Density functional theory (DFT) calculations showed that the P-o-derivative copolymers, i.e., those with outer substitution positions, possessed a more planar conjugated backbone than the P-i-derivative copolymers, i.e., those with inner substitution positions, which enhanced the absorption coefficient and provided higher charge mobility. Moreover, two-dimensional (2D) grazing incidence wide-angle X-ray scattering (GIWAXS) patterns showed clearly that the P-o-derivative blends exhibited strong face-on pi-pi stacking. This ordered polymer packing facilitated charge transport in the vertical direction. In contrast, the P-i-derivative blends were prone to edge-on lamellar stacking. Combining each copolymer with a small molecular acceptor (ITIC-4F), an optimum power conversion efficiency (PCE) of 10% was achieved for the P-o-derivative blend devices, whereas the devices based on the P-i-derivative copolymers exhibited a PCE of only 6.67%. Our comparative research indicates that changing the functional group substitution position could affect molecular packing and molecular properties. This approach provides a path toward the molecular design of more materials for high-performance PSCs.