From Generation to Extraction: A Time-Resolved Investigation of Photophysical Processes in Non-fullerene Organic Solar Cells,The Journal of Physical Chemistry C

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From Generation to Extraction: A Time-Resolved Investigation of Photophysical Processes in Non-fullerene Organic Solar Cells
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2020-09-08 , DOI: 10.1021/acs.jpcc.0c05263
Rokas Jasiu̅nas ₁ , Huotian Zhang ₂ , Jun Yuan _{2,

3} , Xuehong Zhou ₂ , Deping Qian ₂ , Yingping Zou ₃ , Andrius Devižis ₁ , Juozas Šulskus ₄ , Feng Gao ₂ , Vidmantas Gulbinas _{1,

4}

Affiliation

Non-fullerene organic solar cells (NFOSCs) demonstrate record efficiencies exceeding 16%. In comparison with cells with the fullerene-based acceptor, the NFOSCs benefit from a longer wavelength absorption, which leads to a small highest occupied molecular orbital (HOMO) level offset. Here, we use several advanced transient investigation techniques, covering timescale from sub-ps to μs, to address all sequence of processes starting from photoexcitation of donors or acceptors to carrier extraction in several NFOSCs and cells with phenyl-C71-butyric acid methyl ester (PCBM). Though small offsets result in higher open-circuit voltage, we show that at the same time, it limits cell performance because of inefficient hole transfer from excited acceptors to donors and enhanced geminate recombination. We demonstrate that 100 meV HOMO level offset and proper acceptor molecule structures are sufficient for efficient hole transfer (>70%) and for reduction of the geminate recombination losses down to about 20%. Subsequent extraction of unbound charge carriers in all NFOSCs is slightly faster than in cells with PCBM, while non-geminate carrier recombination causing additional losses is slightly slower in the best performing NFOSCs than in cells with PCBM.

中文翻译：

从生成到提取：非富勒烯有机太阳能电池中光物理过程的时间分辨研究

非富勒烯有机太阳能电池（NFOSC）的记录效率超过16％。与具有基于富勒烯的受体的细胞相比，NFOSC受益于更长的波长吸收，这导致较小的最高占据分子轨道（HOMO）水平偏移。在这里，我们使用了几种先进的瞬态研究技术，涵盖了从亚ps到μs的时间范围，以解决从供体或受体的光激发到几个NFOSC和带有苯基C71-丁酸甲酯的细胞中载流子提取开始的所有过程序列（ PCBM）。尽管较小的偏移会导致较高的开路电压，但我们同时表明，由于空穴从受激受体到供体的无效转移以及增强的双子重组，它限制了电池性能。我们证明了100 meV HOMO能级偏移和适当的受体分子结构足以实现有效的空穴转移（> 70％），并能将双链重组损失降低至约20％。随后，在所有NFOSC中，未结合电荷载流子的提取要比具有PCBM的细胞快一些，而在最佳性能的NFOSC中，非成对的载子重组引起额外的损失要比具有PCBM的电池慢一些。

更新日期：2020-10-02

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