Field-Assisted Exciton Dissociation in Highly Efficient PffBT4T-2OD:Fullerene Organic Solar Cells
Field-Assisted Exciton Dissociation in Highly Efficient PffBT4T-2OD:Fullerene Organic Solar Cells
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DOI：
10.1021/acs.chemmater.8b00094
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发表时间：
2018-04-24
影响因子：
8.6
通讯作者：
Vaynzof, Yana
中科院分区：
文献类型：
--
作者：
Weu, Andreas;Hopper, Thomas R.;Vaynzof, Yana
了解有机半导体中电荷产生的光物理是进一步优化有机太阳能电池的关键一步。在具有较大能量偏移量的系统中，电子空穴对的分离相对较好地被理解；然而，在具有低驱动能量的混合物中的光物理仍然不清楚。本文以材料体系PffBT4T-20D：PC71BM为例，说明内建电场在高性能器件的长程电荷分离中起着至关重要的作用。利用稳态和时间分辨光谱技术，我们发现在纯薄膜中，高能势垒阻碍了聚合物激子的解离，阻止了电荷向富勒烯受体的转移。在完整的器件中，由于夹层/接触提供的内置电场和伴随的空间电荷分布，这种势垒被减小。观察到的行为也可能与其他驱动能量较低的系统相关，并强调了使用完整的设备而不仅仅是薄膜进行光物理研究的重要性。
Understanding the photophysics of charge generation in organic semiconductors is a critical step toward the further optimization of organic solar cells. The separation of electron hole pairs in systems with large energy offsets is relatively well-understood; however, the photophysics in blends with low driving energy remains unclear. Herein, we use the material system PffBT4T-2OD:PC71BM as an example to show that the built-in electric field plays a critical role toward long-range charge separation in high-performance devices. By using steady-state and time-resolved spectroscopic techniques, we show that in neat films an energetic barrier impedes polymer exciton dissociation, preventing charge transfer to the fullerene acceptor. In complete devices, this barrier is diminished due to the built-in electric field provided by the interlayers/contacts and accompanying space-charge distribution. The observed behavior could also be relevant to other systems with low driving energy and emphasizes the importance of using complete devices, rather than solely films, for photophysical studies.