Binary All‐polymer Solar Cells with a Perhalogenated‐Thiophene‐Based Solid Additive Surpass 18 % Efficiency

Abstract Morphological control of all‐polymer blends is quintessential yet challenging in fabricating high‐performance organic solar cells. Recently, solid additives (SAs) have been approved to be capable in tuning the morphology of polymer: small‐molecule blends improving the performance and stability of devices. Herein, three perhalogenated thiophenes, which are 3,4‐dibromo‐2,5‐diiodothiophene (SA‐T1), 2,5‐dibromo‐3,4‐diiodothiophene (SA‐T2), and 2,3‐dibromo‐4,5‐diiodothiophene (SA‐T3), were adopted as SAs to optimize the performance of all‐polymer organic solar cells (APSCs). For the blend of PM6 and PY‐IT, benefitting from the intermolecular interactions between perhalogenated thiophenes and polymers, the molecular packing properties could be finely regulated after introducing these SAs. In situ UV/Vis measurement revealed that these SAs could assist morphological character evolution in the all‐polymer blend, leading to their optimal morphologies. Compared to the as‐cast device of PM6 : PY‐IT, all SA‐treated binary devices displayed enhanced power conversion efficiencies of 17.4–18.3 % with obviously elevated short‐circuit current densities and fill factors. To our knowledge, the PCE of 18.3 % for SA‐T1‐treated binary ranks the highest among all binary APSCs to date. Meanwhile, the universality of SA‐T1 in other all‐polymer blends is demonstrated with unanimously improved device performance. This work provide a new pathway in realizing high‐performance APSCs.