Hamid Zeinab, Wadsworth Andrew, Rezasoltani Elham, Holliday Sarah, Azzouzi Mohammed, Neophytou Marios, Guilbert Anne A Y, Dong Yifan, Little Mark S, Mukherjee Subhrangsu, Herzing Andrew A, Bristow Helen, Kline R Joseph, DeLongchamp Dean M, Bakulin Artem A, Durrant James, Nelson Jenny, McCulloch Iain
Department of Chemistry and Centre for Plastic Electronics, Imperial College London, London, W12 0BZ, United Kingdom.
Department of Physics and Centre for Plastic Electronics, Imperial College London, London, SW7 2AZ, United Kingdom.
Adv Energy Mater. 2020;10(8). doi: https://doi.org/10.1002/aenm.201903248.
The temperature dependent aggregation behavior of PffBT4T polymers used in organic solar cells plays a critical role in the formation of a favorable morphology in fullerene-based devices. However, there has been little investigation into the impact of donor/acceptor ratio on morphology tuning, especially for non-fullerene acceptors (NFAs). Herein, the influence of composition on morphology is reported for blends of PffBT4T-2DT with two NFAs, O-IDTBR and O-IDFBR. The monotectic phase behavior inferred from differential scanning calorimetry provides qualitative insight into the interplay between solid-liquid and liquid-liquid demixing. Transient absorption spectroscopy suggests that geminate recombination dominates charge decay and that the decay rate is insensitive to composition, corroborated by negligible changes in open-circuit voltage. Exciton lifetimes are also insensitive to composition, which is attributed to the signal being dominated by acceptor excitons which are formed and decay in domains of similar size and purity irrespective of composition. A hierarchical morphology is observed, where the composition dependence of size scales and scattering intensity from resonant soft X-ray scattering (R-SoXS) is dominated by variations in volume fractions of polymer/polymer rich domains. Results suggest an optimal morphology where polymer crystallite size and connectivity are balanced, ensuring a high probability of hole extraction via such domains.
用于有机太阳能电池的PffBT4T聚合物的温度依赖性聚集行为在基于富勒烯的器件中形成有利形态方面起着关键作用。然而，关于供体/受体比例对形态调控的影响的研究很少，特别是对于非富勒烯受体（NFA）。在此，报道了PffBT4T-2DT与两种NFA（O-IDTBR和O-IDFBR）的共混物中组成对形态的影响。从差示扫描量热法推断出的单溶体相行为为固液和液液分层之间的相互作用提供了定性见解。瞬态吸收光谱表明，双分子复合主导电荷衰减，并且衰减速率对组成不敏感，开路电压的变化可忽略不计，这证实了这一点。激子寿命对组成也不敏感，这归因于该信号由受体激子主导，受体激子在大小和纯度相似的域中形成和衰减，与组成无关。观察到一种分级形态，其中来自共振软X射线散射（R-SoXS）的尺寸尺度和散射强度的组成依赖性由聚合物/富含聚合物的域的体积分数变化主导。结果表明存在一种最佳形态，其中聚合物微晶尺寸和连通性达到平衡，确保通过这些域进行空穴提取的高概率。
