Mixed Metals Slow Down Nonradiative Recombination in Saddle-Shaped Porphyrin Nanorings: A Time-Domain Atomistic Simulation
Mixed Metals Slow Down Nonradiative Recombination in Saddle-Shaped Porphyrin Nanorings: A Time-Domain Atomistic Simulation
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DOI：
10.1021/acs.jpcc.1c04749
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发表时间：
2021-08
期刊：
影响因子：
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通讯作者：
Ritabrata Sarkar;M. Habib;S. Kovalenko;Sougata Pal;O. Prezhdo
中科院分区：
文献类型：
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作者：
Ritabrata Sarkar;M. Habib;S. Kovalenko;Sougata Pal;O. Prezhdo
鞍形锌卟啉纳米环被用作光捕获材料。为了实现高性能，需要快速电荷转移和缓慢电荷复合。快速转移有利于激子有效地分离成自由载流子，从而增强光电流。缓慢的复合减少了电荷和能量损失。我们模拟了这两个过程，结合非绝热（NA）的分子动力学与时间相关的自洽电荷密度泛函紧束缚理论。所得到的皮秒电荷复合时间与实验结果符合得很好。模拟表明，载流子寿命强烈依赖于卟啉纳米环中存在的金属。当卟啉单元仅由Zn中心组成时，模拟寿命为55 ps。如果纳米环含有Zn和Cd，非辐射复合被抑制到200 ps，近4倍。掺入镉部分本地化的光生电荷，削弱NA耦合，并加速声子诱导的电子相干性损失。较重和较慢的Cd也降低了NA耦合。非辐射复合是由低频声子驱动的，C-C伸缩有适度的贡献。我们的研究证明了一个简单的途径，以减少电荷损失的卟啉纳米环的部分交换锌原子与镉，并提供了一个有价值的指导方针，为提高太阳能应用的材料效率。
Saddle-shaped zinc porphyrin nanorings are utilized as light-harvesting materials. To achieve high performance, both fast charge transfer and slow charge recombination are required. Fast transfer favors efficient separation of exciton into free carriers, enhancing photocurrent. Slow recombination reduces charge and energy losses. We simulated both processes using time-dependent self-consistent-charge density functional tight binding theory combined with nonadiabatic (NA) molecular dynamics. The obtained picosecond charge recombination times agree well with experiment. The simulations demonstrate that the carrier lifetime depends strongly on the metals present in the porphyrin nanoring. When the porphyrin units are composed of Zn centers only, the simulated lifetime is 55 ps. If nanorings contain both Zn and Cd, the nonradiative recombination is suppressed to 200 ps, nearly 4 times. Incorporation of Cd partially localizes the photogenerated charges, weakens the NA coupling, and accelerates phonon-induced loss of electronic coherence. The heavier and slower Cd also decreases the NA coupling. The nonradiative recombination is driven by low-frequency phonons, with a moderate contribution from the C–C stretch. Our study demonstrates a straightforward pathway to reducing charge losses in the porphyrin nanorings by partial exchange of Zn atoms with Cd and provides a valuable guideline for improvement of the material efficiency for solar energy applications.