The morphology of the active layer of a bulk heterojunction solar cell, made of a blend of an electron‐donating polymer and an electron‐accepting fullerene derivative, is known to play a determining role in device performance. Here, a combination of molecular dynamics simulations and long‐range corrected density functional theory calculations is used to elucidate the molecular‐scale effects that even minor structural changes to the polymer backbone can have on the “local” morphology; this study focuses on the extent of polymer–fullerene mixing, on their packing, and on the characteristics of the fullerene–fullerene connecting network in the mixed regions, aspects that are difficult to access experimentally. Three representative polymer donors are investigated: (i) poly[(5,6‐difluoro‐2,1,3‐benzothiadiazol‐4,7‐diyl)‐alt‐(3,3′″‐di(2‐octyldodecyl)‐2,2′;5′,2″;5″,2′″‐quaterthiophen‐5,5′″‐diyl)] (PffBT4T‐2OD); (ii) poly[(2,1,3‐benzothiadiazol‐4,7‐diyl)‐alt‐(3,3′″‐di(2‐octyldodecyl)‐2,2′;5′,2″;5″,2′″‐quaterthiophen‐5,5′″‐diyl)] (PBT4T‐2OD), where the fluorine atoms in the benzothiadiazole moieties of PffBT4T‐2OD are replaced with hydrogen atoms; and (iii) poly[(2,2′‐bithiophene)‐alt‐(4,7‐bis((2‐decyltetradecyl)thiophen‐2‐yl)‐5,6‐difluoro‐2‐propyl‐2H‐benzo[d][1,2,3]triazole)] (PT2‐FTAZ), where the sulfur atoms in the benzothiadiazole moieties of PffBT4T‐2OD are replaced with nitrogen atoms carrying a linear C₃H₇ side‐chain; these polymers are mixed with the phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) acceptor. This study also discusses the nature of the charge‐transfer electronic states appearing at the donor–acceptor interfaces, the electronic couplings relevant for the charge‐recombination process, and the electron‐transfer features between neighboring PC₇₁BM molecules.

中文翻译：

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本体异质结太阳能电池：聚合物骨架对聚合物-富勒烯混合和堆积以及富勒烯-富勒烯连接网络的微小结构修饰的影响

由给电子体聚合物和电子接受富勒烯衍生物的混合物制成的块状异质结太阳能电池活性层的形态在器件性能中起着决定性的作用。在这里，结合了分子动力学模拟和长期校正的密度泛函理论计算，以阐明即使是聚合物主链的微小结构变化也可能对“局部”形态产生影响的分子尺度效应。这项研究的重点是聚合物-富勒烯混合的程度，它们的堆积以及混合区域中富勒烯-富勒烯连接网络的特性，这些方面在实验上是很难达到的。研究了三种代表性的聚合物供体：（i）聚[（5,6-二氟-2,1,3-苯并噻二唑-4,7-二基）-alt-（3,3'''-di（2-辛基十二烷基）-2,2'; 5'，2''; 5''，2'''-四噻吩-5,5'''-二基）]（PffBT4T-2OD）; （ii）聚[（2,1,3-苯并噻二唑-4,7-二基）-alt-（3,3'''-di（2-辛基十二烷基）-2,2'; 5'，2''; 5'' ，2'''-四噻吩-5,5'''-二基）]（PBT4T-2OD），其中PffBT4T-2OD的苯并噻二唑部分中的氟原子被氢原子取代；（iii）聚[（2,2'-联噻吩）-alt-（4,7-双（（2-癸基十四烷基）噻吩-2-基）-5,6-二氟-2-丙基-2H-苯并[ d] [1,2,3]三唑]]（PT2-FTAZ），其中PffBT4T-2OD的苯并噻二唑部分中的硫原子被带有线性C ₃ H ₇侧链的氮原子取代；这些聚合物与苯基C ₇₁丁酸甲酯（PC ₇₁BM）受体。这项研究还讨论了在供体-受体界面上出现的电荷转移电子态的性质，与电荷重组过程相关的电子耦合以及相邻PC ₇₁ BM分子之间的电子转移特征。