Toluene Processed All-Polymer Solar Cells with 18% Efficiency and Enhanced Stability Enabled by Solid Additive: Comparison between Sequential-Processing and Blend-Casting

The emergence of polymerized small molecule acceptors (PSMAs) has significantly improved the performance of all-polymer solar cells (all-PSCs). However, the pace of device engineering lacks behind that of materials development, so that a majority of the PSMAs have not fulfilled their potentials. Furthermore, most high-performance all-PSCs rely on the use of chloroform as the processing solvent. For instance, the recent high-performance PSMA named PJ1-γ, with high LUMO and HOMO levels, could only achieve a PCE of 16.1% with a high-energy-level donor (JD40) using chloroform. Herein, we present a methodology combining sequential processing (SqP) with the addition of 0.5%wt PC71BM as a solid additive (SA) to achieve an impressive efficiency of 18.0% for all-PSCs processed from toluene, an aromatic hydrocarbon solvent. Compared to the conventional blend-casting (BC) method whose best efficiency (16.7%) could only be achieved using chloroform, the SqP method significantly boosted the device efficiency using toluene as the processing solvent. In addition, the donor we employ is the classic PM6 that has deeper energy levels than JD40, which provides low energy loss for the device. We compare the results with another PSMA (PYF-T-o) with the same method. Finally, an improved photostability of the SqP devices with the incorporation of SA is demonstrated.