Semi-two-dimensional (semi-2D) benzo[1,2-b:4,5-b′]dithiophene (BDT)-based donor–acceptor copolymers have been regarded as one of the most successful organic semiconductors for photovoltaic applications. In this work, the structure–mobility relationship of four semi-2D BDT-based polymers bearing different kinds of conjugated side chains, including alkyl-monothienyl (T), alkyl-dithienyl (2T), branched alkyl-trithienyl (3T), and alkyl-benzotrithienyl (B3T), is thoroughly investigated. Because of the lower rigidity and the higher spatial mobility, the polymers owning lineally extended conjugated side chains, like PBDT-T and PBDT-2T, still possess certain crystallinity after thermal annealing. However, the crystallinity becomes evanescent as the side-chain conjugation further increases. PBDT-3T and PBDT-B3T bearing a large, branched conjugated side chain become nearly amorphous even after thermal annealing. Despite the low crystallinity, all these semi-2D polymers can still deliver decent hole mobility (μ_h) of >0.1 cm² V^–1 s^–1 after thermal annealing. More interestingly, the amorphous PBDT-3T can deliver a maximum μ_h value of 0.4 cm² V^–1 s^–1, outperforming the value of reference semicrystalline PBDT-T that owns a typical thienyl side chain. Based on the analyses of film morphology and solid-state crystallinity, the hyper-conjugated side chain with intense aggregation tendency is suggested to facilitate the intermittent interchain hopping between polymer chains, which compensates the short-range structural order of low-crystalline polymer to ensure the laudable charge carrier transport property. This work systematically explores the charge carrier transport behaviors of semi-2D polymers with varied biaxially extended conjugated side chains and enlightens a new design strategy to improve the charge carrier transport of low-crystalline polymers.

中文翻译：

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带有不同双轴延伸共轭侧链的苯并二噻吩基共轭聚合物的结构-移动关系

基于半二维（半二维）苯并[1,2-b：4,5-b']二噻吩（BDT）的施主-受主共聚物被认为是光伏应用中最成功的有机半导体之一。在这项工作中，四种带有不同共轭侧链的半基于2D BDT的聚合物的结构-迁移率关系包括烷基-二噻吩基（T），烷基-二噻吩基（2T），支链烷基-三噻吩基（3T）和彻底研究了烷基苯并三噻吩基（B3T）。由于较低的刚性和较高的空间迁移率，具有线性延伸的共轭侧链的聚合物（如PBDT-T和PBDT-2T）在热退火后仍具有一定的结晶度。然而，随着侧链共轭的进一步增加，结晶度逐渐消失。PBDT-3T和PBDT-B3T轴承很大，即使在热退火之后，支链共轭侧链也几乎变为非晶态。尽管结晶度低，但所有这些半二维聚合物仍可提供良好的空穴迁移率（μ热退火后，_h）> 0.1 cm ² V ^–1 s ^–1。更有趣的是，无定形PBDT-3T能够提供的最大μ _ħ值的0.4厘米² V ^-1小号^-1，其性能优于具有典型噻吩基侧链的参比半结晶PBDT-T的值。在分析薄膜形态和固态结晶度的基础上，提出了具有强烈聚集趋势的超共轭侧链，以促进聚合物链之间的间歇性链间跳跃，从而补偿了低结晶聚合物的短程结构顺序，从而确保了值得称赞的电荷载体运输性质。这项工作系统地探索了具有变化的双轴延伸共轭侧链的半二维聚合物的载流子输运行为，并启发了一种新的设计策略，以改善低结晶聚合物的载流子输运。