High-efficiency organic solar cells enabled by an alcohol-washable solid additive

The solvent additive strategy has been widely utilized to boost the power conversion efficiency (PCE) of organic solar cells (OSCs). However, the residual solvent additive in the active layer tends to induce a gradual morphology degradation and further influences the long-term stability of OSCs. Here, a solid additive, 1,4-diiodobenzene (DIB), was introduced to fabricate efficient OSCs. We found that the treatment of DIB can lead to optimized morphology to form a bicontinuous network with intensified intermolecular packing in the donor and acceptor phases. Notably, DIB can be easily removed from the active layer via a simple alcohol washing process and no further post-thermal annealing is needed, which is desirable for large-scale manufacturing of OSCs. As a result, high efficiencies of 17.47% for PM6:Y6 and 18.13% (certified as 17.7%) for PM6:BTP-eC9 binary OSCs are achieved, which are among the highest efficiencies reported for binary OSCs thus far. Moreover, OSCs fabricated with DIB also exhibit superior stability compared with the as-cast and traditional solvent additive processed devices. Additionally, DIB was successfully applied in different active layers, manifesting its general applicability. This work provides a feasible approach to enhance both the efficiency and stability of OSCs.