1] Molecular Materials and Nanosystems and Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands [2] Dutch Polymer Institute P.O. Box 902, 5600 AX Eindhoven, The Netherlands.
BASF Schweiz AG, Schwarzwaldallee 215, CH-4002 Basel, Switzerland.
Nat Commun. 2015 Feb 6;6:6229. doi: 10.1038/ncomms7229.
The photoactive layer of organic solar cells consists of a nanoscale blend of electron-donating and electron-accepting organic semiconductors. Controlling the degree of phase separation between these components is crucial to reach efficient solar cells. In solution-processed polymer-fullerene solar cells, small amounts of co-solvents are commonly used to avoid the formation of undesired large fullerene domains that reduce performance. There is an ongoing discussion about the origin of this effect. To clarify the role of co-solvents, we combine three optical measurements to investigate layer thickness, phase separation and polymer aggregation in real time during solvent evaporation under realistic processing conditions. Without co-solvent, large fullerene-rich domains form via liquid-liquid phase separation at ~20 vol% solid content. Under such supersaturated conditions, co-solvents induce polymer aggregation below 20 vol% solids and prevent the formation of large domains. This rationalizes the formation of intimately mixed films that give high-efficient solar cells for the materials studied.
有机太阳能电池的光活性层由电子给体和电子受体有机半导体的纳米级混合物组成。控制这些组件之间的相分离程度对于获得高效的太阳能电池至关重要。在溶液处理的聚合物-富勒烯太阳能电池中，通常使用少量共溶剂来避免形成降低性能的不期望的大富勒烯域。关于这种效应的起源存在持续的讨论。为了阐明共溶剂的作用，我们结合三种光学测量方法，在实际处理条件下，在溶剂蒸发过程中实时研究层厚度、相分离和聚合物聚集。没有共溶剂，在约 20 体积%固体含量下通过液-液相分离形成大富勒烯富域。在这种过饱和条件下，共溶剂在低于 20 体积%固体含量下诱导聚合物聚集并防止大域的形成。这解释了形成高能量转换效率太阳能电池的紧密混合膜的原因，这些太阳能电池适用于所研究的材料。
