Volatile Additive Strategy Triggering 17.48% Efficient Post‐Treatment‐Free Organic Solar Cells

Active layer morphology is critical to determine the photovoltaic performance of organic solar cells (OSCs), and additive‐assisted morphology optimization is one of the most widely used strategies to fine tune the donor–acceptor network in the active layer. However, the postprocessing procedures and additive residues require additional efforts to maintain the device performance. Herein, a low‐cost, simple structural design and volatile solid additive 2,5‐diiodothiophene is demonstrated to effectively optimize the active layer morphology and prompt the photoelectric conversion efficiency (PCE) of OSCs without any post‐treatment, outperforming the devices fabricated with the prototypical volatile additive 1,4‐diiodobenzene. The 2,5‐diiodothiophene (DIT)‐optimized PM6:Y6 binary OSCs obtain a PCE of 17.48%, accompanied with reduced trap‐assisted charge recombination and balanced charge carrier mobility. In addition, we notice that the bromide and chlorine analogues of DIT can enhance the device performance to a certain extent as well. The findings suggest that the post‐treatment‐free nature of the thiophene‐based processing additives are promising candidates for tuning the active layer morphology, providing simple processability for large‐scale fabrication of OSCs.