Fluorination is one of the most effective ways to manipulate molecular packing, optical bandgap and molecular energy levels in organic semiconductor materials. In this work, different number of fluorine atoms was introduced into the acceptor moiety 2,2′-dithiophene linked 2,1,3-benzothiadiazole, utilizing the alkylthiophene modified dithieno[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b] (DTBDT) as the donor unit, three polymers: PDTBDT-0F-BTs, PDTBDT-2F-BTs and PDTBDT-6F-FBTs were synthesized. With the number of fluorine atoms in each repeat unit of polymers varying from 0 to 2 and then up to 6, PDTBDT-0F-BTs, PDTBDT-2F-BTs and PDTBDT-6F-FBTs exhibited gradually downshifted energy levels and improved dielectric constants (ε_r) from 3.4 to 4.3 to 5.8, further successively increased charge transport mobilities. As a result, the power conversion efficiency (PCE) of the bulk heterojunction organic photovoltaic devices (BHJ-OPV) from the blend films of aforementioned polymers paired with PC₇₁BM were gradually increased from 1.69 for PDTBDT-0F-BTs to 1.89 for PDTBDT-2F-BTs and then to 5.28 for PDTBDT-6F-FBTs. The results show that the continuous insertion of fluorine atoms into the repeating units of the benzothiadiazole conjugated polymer leads to the deepening of HOMO energy level, the increase of ε_r and the increase of charge mobility, which improve the efficiency of charge transfer and electron collection, thus improving the photovoltaic performance of BHJ-OPV.

中文翻译：

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改变氟原子位置和数量对2,1,3-苯并噻二唑基交替共轭聚合物光伏性能的影响

氟化是控制有机半导体材料中分子堆积、光学带隙和分子能级的最有效方法之一。在这项工作中，利用烷基噻吩修饰的二噻吩[2,3- d :2',3'- d ' ，将不同数量的氟原子引入到受体部分2,2'-二噻吩连接的2,1,3-苯并噻二唑中。以]苯并[1,2- b :4,5- b ]（DTBDT）为供体单元，合成了三种聚合物：PDTBDT-0F-BTs、PDTBDT-2F-BTs和PDTBDT-6F-FBTs。随着聚合物每个重复单元中氟原子数量从0到2，然后增加到6，PDTBDT-0F-BT、PDTBDT-2F-BT和PDTBDT-6F-FBT表现出逐渐降低的能级和提高的介电常数（ε _r )从3.4到4.3再到5.8，进一步连续增加电荷传输迁移率。结果，由上述聚合物与PC ₇₁ BM配对的共混膜制成的本体异质结有机光伏器件（BHJ-OPV）的功率转换效率（PCE）从PDTBDT-0F-BT的1.69逐渐增加到PDTBDT的1.89 -2F-BT，然后为 PDTBDT-6F-FBT 为 5.28。结果表明，氟原子连续插入苯并噻二唑共轭聚合物的重复单元中，导致HOMO能级加深，ε _r增大，电荷迁移率增加，从而提高了电荷转移和电子收集的效率。 ，从而提高了BHJ-OPV的光伏性能。