High-Performance Layer-by-Layer organic solar cells enabled by Non-Halogenated solvent with 17.89% efficiency

Sequential layer-by-layer (LbL) deposition method, where ideal vertical morphology can be obtained, is a promising method for the fabrication of highly efficient organic solar cells (OSCs). But most LbL devices are prepared through toxic halogen solvents, hindering OSCs future commercial production. In this work, we have achieved bilayer devices based on PM6/BO-4Cl system for the first time with the non-halogenated solvent (o-xylene). Compared to BHJ devices, the efficiency of LbL devices was enhanced from 16.45 % to 17.03 %. On this basis, L8-BO was chosen as the third component doping into the acceptor layer and the performance of PM6/BO-4Cl: L8-BO ternary devices was further improved, realizing an outstanding PCE of 17.89 %, the highest value so far for halogen-free solvent processed LbL devices. The addition of L8-BO increased photon utilization and formed an alloy with BO-4Cl, while better regulating the donor–acceptor distribution in LbL structure, facilitating exciton dissociation and charge transport. More importantly, the PM6/BO-4Cl: L8-BO-based LbL devices retained 89 % of its original efficiency after 2000 h of placement. Our results demonstrate that tuning the material distribution precisely by LbL method, combined with the use of eco-friendly solvents is an effective way to achieve high performance ternary OSCs that benefiting the development of green energy technologies.