Correlating miscibility, mechanical parameters, and stability of ternary polymer blends for high-performance solar cells

With the rapid emergence of new polymer acceptors, the photovoltaic performance of all-polymer solar cells (all-PSCs) has been greatly improved. However, how to rationally design multicomponent active layers for thermally and mechanically stable all-PSCs remains challenging due to a lack of guiding principles for modulating morphology. In this work, we correlate miscibility between the third components and the host polymer donor/acceptor with the aggregated structure and mechanical behaviors in ternary all-PSCs. The new correlations of miscibility-morphology-thermal stability and miscibility-morphology-mechanical parameters in ternary blend films are established. Based on material-specific interaction parameters and microstructural features, we present the first classification of four types of ternary blends (including an over 18% efficiency system) and ascertain the corresponding models for predicting mechanical parameters. The miscibility-based mechanical models also exhibit good quantitative agreement with experimental data from two newly reported ternary systems. As such, the established miscibility-function relationships are helpful to predict the mechanical properties and stability of organic photovoltaic devices based on multicomponent systems.