多相半结晶微结构驱动纯塑料半导体中的激子解离
Multi-phase semicrystalline microstructures drive exciton dissociation in neat plastic semiconductors
AI总结：
本研究通过时间分辨PL光谱揭示P3HT中分子量依赖的微结构（单相与两相）如何影响电荷光生与激子解离，发现两相界面无序区高度离域激子的非本征解离产率及分布与微结构密切相关。
摘要：
大分子半导体的光电性质从根本上取决于其固态微结构。例如，分子量分布通过多种微结构影响聚合物半导体性质；低重均分子量聚合物形成不相连的伸展链晶体，通常呈石蜡结构。由于相对短链大分子的非缠结特性，这导致多晶单相形态。相反，在高分子量材料中，平均链长大于缠结长度，形成由结晶部分嵌入 largely unordered（无定形）区域组成的两相形态。我们通过时间分辨光致发光（PL）光谱研究不同分子量的纯规整聚(3-己基噻吩)（P3HT）中的电荷光生过程。在10 K下，源自长寿命电荷对复合的PL在微秒时间尺度上衰减。振幅和衰减速率分布均强烈依赖于分子量。在以单相伸展链微结构为主的薄膜中，由于光生电荷产率降低，延迟PL被抑制，且其衰减明显快于两相微结构。然而，无论分子量如何，电荷复合均使扭转无序链中的单线态激子再生，形成比稳态集合中耦合更强的光物理聚集体，延迟PL线形类似于稳态石蜡形态。我们得出结论：结晶相与无定形相之间无序区域中高度离域的激子发生非本征解离，其产率和空间分布与微结构密切相关。
英文摘要：
The optoelectronic properties of macromolecular semiconductors depend fundamentally on their solid-state microstructure. For example, the molecular-weight distribution influences polymeric- semiconductor properties via diverse microstructures; polymers of low weight-average molecular weight (Mw) form unconnected, extended-chain crystals, usually of a paraffinic structure. Because of the non-entangled nature of the relatively short-chain macromolecules, this leads to a polycrystalline, one-phase morphology. In contrast, with high-Mw materials, where average chain lengths are longer than the length between entanglements, two-phase morphologies, comprised of crystalline moieties embedded in largely unordered (amorphous) regions, are obtained. We investigate charge photogeneration processes in neat regioregular poly(3-hexylthiophene) (P3HT) of varying Mw by means of time-resolved photoluminescence (PL) spectroscopy. At 10 K, PL originating from recombination of long-lived charge pairs decays over microsecond timescales. Both the amplitude and decay rate distribution depend strongly on Mw. In films with dominant one-phase chain-extended microstructures, the delayed PL is suppressed as a result of a diminished yield of photoinduced charges, and its decay is significantly faster than in two-phase microstructures. However, independent of Mw, charge recombination regenerates singlet excitons in torsionally disordered chains forming more strongly coupled photophysical aggregates than those in the steady-state ensemble, with delayed PL lineshape reminiscent of that in paraffinic morphologies at steady state. We conclude that highly delocalized excitons in disordered regions between crystalline and amorphous phases dissociate extrinsically with yield and spatial distribution that depend intimately upon microstructure.
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