Optimizing mechanical stretchability and photovoltaic performance in all-polymer solar cells from a two-donor polymer blend

In recent years, the power conversion efficiency of all-polymer organic photovoltaic cells (OPVs) has surpassed 19%, reaching a level suitable for commercial applications. To meet the dual requirements of high efficiency and high stretchability for wearable applications, ternary blending strategies have been widely used to improve the tensile properties of all-polymer OPVs. However, up to now, synergistic optimization of both photovoltaic and mechanical properties has seldom been realized. Herein, we introduce a long-branched side chain-containing PM6-like donor polymer, PM6-OD, into a PM6:PY-IT blend to construct stretchable active layers for allpolymer OPVs. When the weight content of PM6-OD in the donor polymers is 20%, both the photovoltaic and mechanical properties of the ternary solar cell are maximized. The variation of the mechanical and photovoltaic properties with the PM6-OD content in the donor was analyzed through grazing-incidence X-ray scattering and thin-film mechanical measurements to gain a deeper understanding of the intrinsic relationship between blend microstructure and mechanical properties. In addition, we prove that the data points of elastic moduli match well with the Kerner-Davis model. This work provides new guidance for the construction of high-efficiency, stretchable OPVs and has a promoting effect on the application of OPVs in wearable/stretchable electronics.