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Effects of Fluorination on Exciton Binding Energy and Charge Transport of π-Conjugated Donor Polymers and the ITIC Molecular Acceptor: A Theoretical Study
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2019-03-06 , DOI: 10.1021/acs.jpcc.8b12261 Leandro Benatto 1 , Marlus Koehler 1
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2019-03-06 , DOI: 10.1021/acs.jpcc.8b12261 Leandro Benatto 1 , Marlus Koehler 1
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The intelligent addition of fluorine atoms in the chemical structure of conjugated polymers has been a popular approach to improve the efficiency of organic photovoltaic (OPV) devices. Recently, this strategy has been extended to nonfullerene acceptor (A) molecules in the best-performing bulk heterojunction (BHJ) devices. Yet, many details involved in the role of fluorination to enhance the photovoltaic response of organic semiconductors are still unclear. Here, we theoretically investigate the changes in the key properties of the representative fluorinated oligomers of polymers commonly used as donors (D) in BHJ-based OPVs. We then extend our analysis to consider the fluorination of ITIC, a very promising nonfullerene acceptor. We focus on the variation of the exciton binding energy (Eb) with the fluorination of an oligomer (molecule). Our calculations indicate that the fluorine substitution tends to lower the exciton binding energy which can enhance charge generation after light absorption. Considering the complexes of two oligomers (molecules), we also investigate the effects of fluorination on charge transport. We found that the intermolecular binding energy is considerably higher for the oligomers (molecules) with fluorine atoms. The increased electronic coupling tends to induce a better packing along the π–π direction which can explain the differences observed in the morphology of thin solid films. The calculation of the hole mobility for the oligomers (and electronic coupling for the acceptor molecules) showed higher values with fluorination. Our results are consistent with the space charge-limited current measurements performed in fluorinated conjugated materials and highlight the main reasons behind the better performance of fluorinated BHJ devices.
中文翻译：
氟化对π共轭给体聚合物和ITIC分子受体的激子结合能和电荷输运的影响：理论研究
在共轭聚合物的化学结构中智能添加氟原子已成为提高有机光伏（OPV）装置效率的流行方法。最近，此策略已扩展到性能最佳的本体异质结（BHJ）器件中的非富勒烯受体（A）分子。然而，涉及氟化作用以增强有机半导体的光伏响应作用的许多细节仍不清楚。在这里，我们从理论上研究了通常用作基于BHJ的OPV的供体（D）的聚合物的代表性氟化低聚物的关键性能的变化。然后，我们将分析范围扩展到考虑ITIC（非常有前途的非富勒烯受体）的氟化。我们关注激子结合能（Eb）与低聚物（分子）的氟化作用。我们的计算表明，氟取代趋于降低激子结合能，这可以增强光吸收后的电荷产生。考虑到两个低聚物（分子）的复合物，我们还研究了氟化作用对电荷传输的影响。我们发现，具有氟原子的低聚物（分子）的分子间结合能要高得多。电子耦合的增加趋向于沿π-π方向产生更好的堆积，这可以解释在固体薄膜形态上观察到的差异。低聚物的空穴迁移率的计算（以及受体分子的电子偶联）显示出更高的氟化值。
更新日期：2019-03-07
中文翻译：
氟化对π共轭给体聚合物和ITIC分子受体的激子结合能和电荷输运的影响：理论研究
在共轭聚合物的化学结构中智能添加氟原子已成为提高有机光伏（OPV）装置效率的流行方法。最近，此策略已扩展到性能最佳的本体异质结（BHJ）器件中的非富勒烯受体（A）分子。然而，涉及氟化作用以增强有机半导体的光伏响应作用的许多细节仍不清楚。在这里，我们从理论上研究了通常用作基于BHJ的OPV的供体（D）的聚合物的代表性氟化低聚物的关键性能的变化。然后，我们将分析范围扩展到考虑ITIC（非常有前途的非富勒烯受体）的氟化。我们关注激子结合能（Eb）与低聚物（分子）的氟化作用。我们的计算表明，氟取代趋于降低激子结合能，这可以增强光吸收后的电荷产生。考虑到两个低聚物（分子）的复合物，我们还研究了氟化作用对电荷传输的影响。我们发现，具有氟原子的低聚物（分子）的分子间结合能要高得多。电子耦合的增加趋向于沿π-π方向产生更好的堆积，这可以解释在固体薄膜形态上观察到的差异。低聚物的空穴迁移率的计算（以及受体分子的电子偶联）显示出更高的氟化值。
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