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.