We present two-dimensional white-light spectroscopy (2DWL) measurements of binary and ternary bulk heterojunctions of the polymer donor PM6 mixed with state-of-the-art nonfullerene acceptors Y6 or IT4F. The ternary film has a shorter lifetime and faster spectral diffusion than either of the binary films. 2D line shape analysis of the PM6 ground state bleach with a Kubo model determines that all three films have similar amplitudes of fluctuations (Δ = 0.29 fs^–1) in their transition frequencies, but different relaxation times (ranging from 102 to 24 fs). The ternary film exhibits faster dynamics than either of the binary films. The short lifetime of the ternary blend is consistent with increased photoexcitation transfer and the fast frequency fluctuations are consistent with structural dynamics of aliphatic side chains. These results suggest that the femtosecond fluctuations of PM6 are impacted by the choice of the acceptor molecules. We hypothesize that those dynamics are either indicative, or perhaps the initial source, of structural dynamics that ultimately contribute to solar cell operation.

中文翻译：

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二维白光光谱探测二元和三元有机光伏薄膜 PM6 域的超快波动

我们提出了聚合物供体 PM6 与最先进的非富勒烯受体 Y6 或 IT4F 混合的二元和三元本体异质结的二维白光光谱 (2DWL) 测量。三元薄膜比任何一种二元薄膜具有更短的寿命和更快的光谱扩散。使用 Kubo 模型对 PM6 基态漂白剂进行的 2D 线形分析确定，所有三种薄膜都具有相似的波动幅度 (Δ = 0.29 fs ^–1) 的跃迁频率，但弛豫时间不同（范围从 102 到 24 fs）。三元薄膜表现出比任何一种二元薄膜更快的动态。三元混合物的短寿命与增加的光激发转移一致，快速的频率波动与脂肪族侧链的结构动力学一致。这些结果表明 PM6 的飞秒波动受受体分子选择的影响。我们假设这些动力学要么是最终有助于太阳能电池运行的结构动力学的指示性来源，要么是最初的来源。