An Improved Performance of All Polymer Solar Cells enabled by Sequential Processing via Non-halogenated Solvents

Polymer acceptors based on the polymerization of small-molecule acceptor (PSMAs) have developed rapidly in recent years. All-polymer solar cells (all-PSCs) composed of PSMAs and polymer donors not only retain the excellent mechanical properties, but also have better morphological properties than traditional polymer acceptors such as N2200. However, since PSMAs are generally not highly polymerized, their electron mobilities are generally lower than the hole mobilities of the high-molecular-weight polymer donors they are used with. In this work, we apply the sequential processing (SqP) method and use toluene as the processing solvent to prepare PSMA-based all-PSCs, which effectively improves the electron mobility and shows much higher efficiency (15.8 %) than the SqP device prepared from chloroform (13.9 %) – the conventional solvent used for high-performance PSMAs. Not only that, the efficiency of the toluene-processed SqP device is also higher than that of the device prepared by the traditional blending-casting (BC) method (14.2 %). In addition, for the first time, we reveal the film formation process of all-polymer active layers prepared by the SqP method using the in situ UV-Vis absorption technique, and investigate the vertical phase separation and the rate of exciton generation across the device using film-depth-dependent absorption spectroscopy, which systematically explained the effect of increased mobility on device parameters. This methodology is applied in two different all-polymer systems, namely, PM6:PYF-T-o and PM6:PY-IT, and both systems manifest the same conclusion.