Triplet Excitons in Pentacene Are Intrinsically Difficult to Dissociate via Charge Transfer,The Journal of Physical Chemistry C

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Triplet Excitons in Pentacene Are Intrinsically Difficult to Dissociate via Charge Transfer
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2020-11-17 , DOI: 10.1021/acs.jpcc.0c08537
Natalie A. Pace _{1,

2} , Tyler T. Clikeman ₃ , Steven H. Strauss ₃ , Olga V. Boltalina ₃ , Justin C. Johnson _{1,

4} , Garry Rumbles _{1,

2,

4} , Obadiah G. Reid _{1,

4}

Affiliation

Singlet fission (SF) has the potential to bypass the Shockley–Queisser limit for solar cell efficiency through the production of two electron–hole pairs per photon. However, in polycrystalline pentacene this goal is hindered by slow charge transfer from triplets (≤10⁷ s^–1) after SF. In this paper we show that slow charge transfer is an intrinsic property of triplet states in this material and most likely not connected with the triplet pair states that may result from singlet fission. We compare two perylene diimide/pentacene charge transfer systems that differ only by triplet generation mechanism: SF versus intersystem crossing (ISC), sensitized by using a soluble lead phthalocyanine derivative. We use time-resolved microwave conductivity (TRMC) to measure the charge yield in each system and transient absorption (TA) to follow the triplet population dynamics. These experiments are described by a single global kinetic model, with most of its parameters fixed via control experiments. While we observe modest differences in the charge-transfer rate constants between each sample, 4–10× as a function of triplet generation mechanism, all samples remain far below the predicted diffusion-limited rate constant of 10⁷–10⁸ s^–1.

中文翻译：

并五苯中的三重态激子本质上难以通过电荷转移解离

单线态裂变（SF）有可能通过每个光子产生两个电子-空穴对来绕过Shockley-Queisser对太阳能电池效率的限制。但是，在多并五苯中，此目标受到三重态电荷转移缓慢的影响（≤10 ⁷ s ^–1）。在本文中，我们证明了缓慢的电荷转移是这种材料中三重态的固有性质，很可能与单重态裂变可能导致的三重态对无关。我们比较了两个per二酰亚胺/并五苯电荷转移系统，它们的区别仅在于三重态产生机理：SF与系统间交叉（ISC），通过使用可溶性铅酞菁衍生物敏化。我们使用时间分辨的微波电导率（TRMC）来测量每个系统中的电荷产率，并使用瞬态吸收（TA）来跟踪三重态种群动态。这些实验是通过一个单一的全局动力学模型来描述的，其中大部分参数都是通过对照实验确定的。虽然我们观察到每个样品之间的电荷转移速率常数存在适度的差异，⁷ –10 ⁸ s ^–1。

更新日期：2020-12-03

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