Tuning charge transfer and recombination in exTTF/CNT nanohybrids by choice of chalcogen: A time-domain density functional analysis
Tuning charge transfer and recombination in exTTF/CNT nanohybrids by choice of chalcogen: A time-domain density functional analysis
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DOI：
10.1063/5.0034561
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发表时间：
2021-01
影响因子：
3.2
通讯作者：
Ritabrata Sarkar;Md Habib;Sougata Pal;O. Prezhdo
中科院分区：
文献类型：
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作者：
Ritabrata Sarkar;Md Habib;Sougata Pal;O. Prezhdo
由碳纳米管(CNTs)和有机分子组成的超分子纳米杂化材料具有广泛的应用前景。我们研究了在碳纳米管表面固定的扩展四硫富瓦烯(ExTTF)的电荷分离和复合动力学，并通过与富硒四硫富瓦烯(ExTSeF)类似物的比较研究了硫原子在碳纳米管表面固定的电荷分离和复合动力学。用含时紧束缚密度泛函理论和非绝热分子动力学相结合的方法，我们证明了exTTF的光激发导致电子转移(ET)进入碳纳米管的导带，而碳纳米管的激发导致空穴转移(HT)到exTTF。在这两个系统中，ET都是亚皮秒的，而高温转移时间强烈地依赖于硫化物。模拟的ET时间与已有的实验结果相吻合。与exTTF/CNT相比，exTSeF/CNT具有更小的能隙、更大的非绝热电荷-声子耦合和更长的相干时间，从而使激发的CNT的高温加速两个数量级。相比之下，电荷分离态的非辐射衰变发生在纳秒时间尺度上。由于较弱的非绝热耦合和较短的相干时间，在exTTF/CNT杂化中，电子和空穴的复合速度要慢一个数量级。这种耦合较弱，因为高频声子不那么活跃。由于更广泛的低频模式的参与，相干性更短。最新的原子量子动力学模拟表明，硫族原子对分子/碳纳米管杂化材料中光生载流子的分离和复合动力学有很强的影响。这些见解为优化现代纳米材料的光伏效率提供了有价值的指导。
Supramolecular nanohybrids composed of carbon nanotubes (CNTs) and organic molecules are appealing candidates for many applications. We investigate charge separation and recombination dynamics in extended tetrathiafulvalene (exTTF), a well-known sulfur (S)-rich electron donor, immobilized on a CNT surface, and study the role of the chalcogen atom by comparing with the selenium (Se)-rich tetraselenafulvalene (exTSeF) analog. Using real-time time-dependent tight-binding density-functional theory combined with nonadiabatic molecular dynamics, we show that photo-excitation of exTTF results in electron transfer (ET) into the CNT conduction band, while CNT excitation leads to hole transfer (HT) to exTTF. The ET is sub-picosecond in both systems, while the HT transfer time depends strongly on the chalcogen. The simulated ET times agree with available experiments. HT from the excited CNT is accelerated by two orders of magnitude more in exTSeF/CNT than exTTF/CNT, because of smaller energy gap, larger nonadiabatic charge–phonon coupling, and longer coherence time. In comparison, nonradiative decay of the charge-separated state takes place on nanosecond time scales. Electrons and holes recombine more slowly by an order of magnitude in the exTTF/CNT hybrid because of weaker nonadiabatic coupling and shorter coherence time. The coupling is weaker since high frequency phonons are less active. The coherence is shorter due to participation of a broader spectrum of low-frequency modes. The state-of-the-art atomistic quantum dynamics simulation demonstrates the strong influence of the chalcogen atom on the separation and recombination dynamics of photo-generated carriers in the molecule/CNT hybrids. The insights provide valuable guidelines for optimization of photovoltaic efficiency in modern nanoscale materials.