Improving the Photovoltaic Performance of Nonhalogenated Solvent-Processed All-Polymer Solar Cells via a Layer-by-Layer Strategy

All-polymer solar cells (APSCs) have gained significant attention due to their superior device stability and mechanical robustness. Realizing state-of-the-art efficiencies in APSCs generally relies on using halogenated solvent processing to achieve the desired morphology. However, these solvents pose potential risks to human health and the environment. Nonhalogenated solvents, which are relatively less toxic, exhibit limited solubility for conjugated polymer materials with long molecular chains, resulting in difficulties in forming ordered molecule packing and uniformly blending films due to the high viscosity of the solution. Thus, the performances of APSCs processed with nonhalogenated solvents still are lagging. Herein, employing an all-polymer system with PM6 as the donor and PY-IT as the acceptor, we implemented a layer-by-layer (LBL) strategy using high-boiling-point o-xylene and toluene to dissolve and cast the donor and acceptor, respectively. This approach enhanced the film formation by optimizing the solution viscosity and preventing mutual entanglement among the polymer chains. By selection of a suitable solvent for PY-IT, erosion of the PM6 film was inhibited, thereby achieving an ideal vertical distribution in the active layer. Consequently, the LBL device achieved an efficient power conversion efficiency of 16.6%, surpassing that of bulk-heterojunction devices. This study demonstrated that the LBL strategy is a viable method to improve the performance of nonhalogenated solvent-processed APSCs.