Yang Dan, Cao Bing, Müller-Buschbaum Peter
Department of Chemistry, University of Alberta, 11227 Saskatchewan Drive, Edmonton, Alberta T6G 2G2, Canada.
National Institute for Nanotechnology, National Research Council Canada, 11421 Saskatchewan Drive, Edmonton, Alberta T6G 2M9, Canada.
ACS Appl Mater Interfaces. 2021 Sep 29;13(38):46134-46141. doi: 10.1021/acsami.1c12790. Epub 2021 Sep 14.
Organic photovoltaics are typically composed of at least four different materials, including the donor and acceptor components of the bulk heterojunction, the interfacial layers at each electrode, the electrodes themselves, and solution additives that may persist in the final sandwich structure. The interplay of surface energies between these different layers is profoundly complex, as the deposition and annealing of one layer on top of another may be influenced by the surface energy of these interfaces. While the energy levels of one layer with respect to adjacent layers are important to facilitate charge separation and collection at the electrodes, the relative surface energies of the interfaces in contact with the multicomponent bulk heterojunction can be beneficial or disadvantageous, or be neutral, with respect to the performance of the OPV device. Because the bulk heterojunction is a mixture of donor and acceptor polymers and/or small molecules, the accumulation of one of the components on the underlying electrode interface can be driven by surface energy considerations. A donor- or acceptor-rich interface may affect charge carrier flow to the electrode, thus affecting the overall efficiency. Here, ITO/PEDOT:PSS electrodes in forward organic photovoltaic devices are treated with five different thin interfacial layers to change the relative surface energy of this electrode with respect to the adjacent bulk heterojunction. Contact angle measurements with four probe liquids enable calculation of the surface energies, and the results are compared with the performance of forward-biased organic photovoltaic devices. Time-of-flight secondary ion mass spectrometry results substantiate the predictions of gradients in the bulk heterojunction layers, and grazing-incidence wide-angle X-ray scattering measurements show the impact on the polymer crystallites. Thus, a simple algorithm based on surface energy considerations may inform which interfacial layer for a given bulk heterojunction in an organic photovoltaic device can be the most appropriate.
有机光伏器件通常由至少四种不同材料组成，包括本体异质结的给体和受体组分、每个电极处的界面层、电极本身以及可能存在于最终三明治结构中的溶液添加剂。这些不同层之间表面能的相互作用极其复杂，因为一层在另一层之上的沉积和退火可能会受到这些界面表面能的影响。虽然一层相对于相邻层的能级对于促进电荷在电极处的分离和收集很重要，但与多组分本体异质结接触的界面的相对表面能对于有机光伏器件的性能可能是有利的、不利的或中性的。由于本体异质结是给体和受体聚合物和/或小分子的混合物，一种组分在下层电极界面上的积累可能受表面能因素驱动。富含给体或受体的界面可能会影响电荷载流子流向电极，从而影响整体效率。在此，正向有机光伏器件中的ITO/PEDOT:PSS电极用五种不同的薄界面层进行处理，以改变该电极相对于相邻本体异质结的相对表面能。使用四种探针液体进行接触角测量可计算表面能，并将结果与正向偏置有机光伏器件的性能进行比较。飞行时间二次离子质谱结果证实了本体异质结层中梯度的预测，掠入射广角X射线散射测量显示了对聚合物微晶的影响。因此，基于表面能考虑的简单算法可以告知对于有机光伏器件中给定的本体异质结，哪种界面层可能是最合适的。
