Singlet Exciton Lifetimes in Conjugated Polymer Films for Organic Solar Cells
Singlet Exciton Lifetimes in Conjugated Polymer Films for Organic Solar Cells
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DOI：
10.3390/polym8010014
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发表时间：
2016-01-01
期刊：
影响因子：
5
通讯作者：
Durrant, James R.
中科院分区：
文献类型：
--
作者：
Dimitrov, Stoichko D.;Schroeder, Bob C.;Durrant, James R.
共轭聚合物薄膜中单重态激子的寿命是有机太阳能电池器件优化设计中要考虑的一个关键因素。它决定了聚合物薄膜中的单重态激子扩散长度，并直接影响到有机太阳能电池器件产生的光电流。然而，人们对控制单重态激子寿命的材料性质知之甚少，我们的大部分知识都来自于对有机小分子的研究。本文简要介绍了共轭聚合物薄膜中激发态的性质，并对16种半导体聚合物的单重态激子寿命进行了分析。用超快瞬时吸收光谱测量了其中7种聚合物的激子寿命，并与文献中发现的7种最常见的光活性聚合物的寿命进行了比较。激子衰减率与聚合物光学带隙之间的对数关系图揭示了寿命与带隙之间的中等相关性，从而表明能隙定律可能适用于这些体系。因此，这表明小带隙聚合物可能会受到激子寿命短的影响，这可能会限制它们在有机太阳能电池器件中的性能。此外，对一种带隙较小的二酮吡咯共聚物，研究了薄膜结晶度对激子寿命的影响。观察到聚合物薄膜结晶度的增加导致激子寿命和光学带隙的减小，再次符合能隙定律。
The lifetime of singlet excitons in conjugated polymer films is a key factor taken into account during organic solar cell device optimization. It determines the singlet exciton diffusion lengths in polymer films and has a direct impact on the photocurrent generation by organic solar cell devices. However, very little is known about the material properties controlling the lifetimes of singlet excitons, with most of our knowledge originating from studies of small organic molecules. Herein, we provide a brief summary of the nature of the excited states in conjugated polymer films and then present an analysis of the singlet exciton lifetimes of 16 semiconducting polymers. The exciton lifetimes of seven of the studied polymers were measured using ultrafast transient absorption spectroscopy and compared to the lifetimes of seven of the most common photoactive polymers found in the literature. A plot of the logarithm of the rate of exciton decay vs. the polymer optical bandgap reveals a medium correlation between lifetime and bandgap, thus suggesting that the Energy Gap Law may be valid for these systems. This therefore suggests that small bandgap polymers can suffer from short exciton lifetimes, which may limit their performance in organic solar cell devices. In addition, the impact of film crystallinity on the exciton lifetime was assessed for a small bandgap diketopyrrolopyrrole co-polymer. It is observed that the increase of polymer film crystallinity leads to reduction in exciton lifetime and optical bandgap again in agreement with the Energy Gap Law.