A series of perylenediimide (PDI) dimers are evaluated as acceptors for organic photovoltaic (OPV) cells. The materials are characterized using a wide variety of physical and computational techniques. These dimers are first linked at the bay position of each PDI molecule via an aromatic spacer; subsequent photocyclization affords ring-fused dimers. Thus, photocyclization of the thiophene-linked dimer 2,5-bis-[N,N′-bis-perylenediimide-1-yl]-thiophene (>T1) affords the twisted acceptor [2,3-b:2′,3′-d]-bis-[N,N′-bis-perylenediimide-1,12-yl]-thiophene (>T2), while photocyclization of the thienothiophene-linked dimer, 2,5-bis-[N,N′-bis-perylenediimide-1-yl]-thienothiophene (>TT1) affords the planar acceptor [2,3-b:2′,3′-d]-bis-[N,N′-bis-perylenediimide-1,12-yl]-thienothiophene (>TT2). Furthermore, a dimer linked by a phenylene group, 1,4-bis-[N,N′-bis-perylenediimide-1-yl]-benzene (>Ph1), can be selectively photocyclized to form either the twisted dimer, [1,2:3,4]-bis-[N,N′-bis-perylenediimide-1,12-yl]-benzene (>Ph1a) or the planar dimer [1,2:4,5]-bis-[N,N′-bis-perylenediimide-1,12-yl]-benzene (>Ph2b). Ring-fusion results in increased electronic coupling between the PDI units, and increased space-charge limited thin film electron mobility. While charge transport is efficient in bulk-heterojunction blends of each dimer with the polymeric donor >PBDTT-FTTE, in the case of the twisted dimers ring fusion leads to a significant decrease in geminate recombination, hence increased OPV photocurrent density and power conversion efficiency. This effect is not observed in planar dimers where ring fusion leads to increased crystallinity and excimer formation, decreased photocurrent density, and decreased power conversion efficiency. These results argue that ring fusion is an effective approach to increasing OPV bulk-heterojunction charge carrier generation efficiency in PDI dimers as long as they remain relatively amorphous, thereby suppressing excimer formation and coulombically trapped charge transfer states.
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机译:一系列of二酰亚胺(PDI)二聚体被评估为有机光伏(OPV)电池的受体。使用多种物理和计算技术来表征材料。这些二聚体首先通过芳族间隔基连接在每个PDI分子的间隔位置。随后的光环化提供了环稠合的二聚体。因此,噻吩连接的二聚体2,5-双-[N,N'-双-二酰亚胺-1-基]-噻吩(> T1 strong>)的光环化提供了扭曲的受体[2,3- b:2',3'-d]-双-[N,N'-双-二酰亚胺-1,12-基]-噻吩(> T2 strong>),而噻吩并噻吩连接的二聚体的光环化,2,5-双-[N,N'-双-二酰亚胺-1-基]-噻吩并噻吩(> TT1 strong>)提供平面受体[2,3-b:2',3'- d]-双-[N,N'-双-二酰亚胺-1,12-基]-噻吩并噻吩(> TT2 strong>)。此外,由亚苯基连接的二聚体1,4-双-[N,N'-双-二酰亚胺-1-基]-苯(> Ph1 strong>)可以选择性地光环化以形成扭曲的二聚体[1,2:3,4]-双-[N, N em>'-双-二酰亚胺-1,12-yl]-苯(> Ph1a strong> )或平面二聚体[1,2:4,5]-双-[ N em>, N em>'-双-二酰亚胺-1,12-基]-苯( > Ph2b strong>)。环稠合导致PDI单元之间的电子耦合增加,并且空间电荷受限的薄膜电子迁移率增加。尽管在每个二聚体与聚合物供体> PBDTT-FTTE strong>的本体-异质结共混物中电荷转移是有效的,但在扭曲的二聚体环融合的情况下,显着降低了重组,从而增加了OPV光电流密度和功率转换效率。在平面二聚体中未观察到此效应,其中环熔合导致结晶度和准分子形成增加,光电流密度降低和功率转换效率降低。这些结果表明,环熔合是提高PDI二聚体中OPV体-异质结电荷载流子生成效率的有效方法,只要它们保持相对非晶态即可,从而抑制了受激准分子的形成和库仑捕获的电荷转移状态。
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