Balance between Energy Transfer and Exciton Separation in Ternary Organic Solar Cells with Two Conjugated Polymer Donors
Balance between Energy Transfer and Exciton Separation in Ternary Organic Solar Cells with Two Conjugated Polymer Donors
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DOI：
10.1021/acsaem.0c00740
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发表时间：
2020-06-22
影响因子：
6.4
通讯作者：
Uddin, Ashraf
中科院分区：
文献类型：
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作者：
Duan, Leiping;Zhang, Yu;Uddin, Ashraf
三元策略作为有机太阳能电池提高器件性能的直接途径，引起了业界的广泛关注。三元策略通常侧重于加工与二元系统具有互补吸收的第三种吸光材料。然而，研究吸收光谱与二元对应物相似的第三组分对于深入了解第三组分性能改善的机制同样重要。在这项工作中，我们填补了这一空白，并衍生出一种由PTB7-Th和PffBT4T-2OD两种共轭聚合物给体材料和非富勒烯受体材料IEICO-4F组成的三元器件。优化后的三元器件的平均功率转换效率值达到12.1%，比其对应物PTB7-Th:IEICO-4F高出约16%。对于吸收光谱与PTB7-Th相似的PffBT4T-2OD的第三组分，发现J（sc）的增加是主要的性能增强因素。进一步的研究表明，优化后的三元器件的L-sc的提高主要来自光吸收能力的提高、电流提取过程的改善、电荷输运过程的改善以及非辐射复合的抑制。此外，在优化三元共混比时，发现激子分离过程和能量传递过程之间存在平衡。优化后的三元器件有望达到这一平衡点，从而表现出器件性能的增强。形貌研究表明，加入po4t - 2od可以调节活性层的形貌，提高活性层的结晶度。优化后的三元共混物，供体和受体形态混合良好，畴尺寸小，结晶程度略有提高，进一步解释了其最佳器件性能。
The ternary strategy as a straightforward way for organic solar cells to improve the device performance attracts many interests in the field. The ternary strategy usually focuses on processing the third light-absorbing material having a complementary absorption to the binary system. However, studying the third component with similar absorption spectra as those of the binary counterpart is equally essential to understand the in-depth mechanism of the performance improvement from the third component. In this work, we filled this blank and derived a type of ternary device consisting of two conjugated polymer donor materials of PTB7-Th and PffBT4T-2OD and the nonfullerene acceptor material IEICO-4F. The average power conversion efficiency value of the optimized ternary device reached 12.1%, which is around 16% higher than that of its PTB7-Th:IEICO-4F binary counterpart. For the third component of PffBT4T-2OD containing a similar absorption spectrum as that of PTB7-Th, it was found that the J(sc) increase contributes to the primary performance enhancement. Further investigations indicate that the L-sc increase in the optimized ternary device mainly came from the improved light absorption ability, current extraction process, charge transport process, and suppressed nonradiative recombination. Moreover, there is a balance found between the exciton separation process and the energy transfer process when optimizing ternary blend ratios. The optimized ternary device is suspected to reach this balance point and thus exhibits the enhancement in device performance. Morphology investigation reveals that the addition of POT4T-2OD can tune the morphology and increase the crystallinity in the active layer. The optimized ternary blend shows a well-mixed donor and acceptor morphology with small domain size and slightly increased crystallization, which further explains its best device performance.