Batch-Reproducible and Thickness-Insensitive Mesopolymer Zwitterion Interlayers for Organic Solar Cells

Zwitterionic polymers or small molecules are a class of widely used interlayer materials in organic solar cells (OSCs). It is challenging to develop such materials that combine good film-forming property, high batch-to-batch reproducibility, and broad thickness processing window in device applications. Herein, we designed and synthesized two self-doped conjugated mesopolymer zwitterions (CMZs), namely, MT₂PDIMz and MT₂PDINz (PDI = perylene-diimide, M = mesopolymer, T₂ = dithiophene, Mz = imidazolium zwitterion, Nz = ammonium zwitterion). Both show good processability and effectively reduce the work function of metal electrodes. The substitution of imidazolium cations with ammonium cations on the side-chains can further modulate the solution assembly and self-doping effect of CMZs, enabling improved interfacial compatibility with active layers and higher electron mobility in MT₂PDIMz. The versatility of CMZs interlayers for OSCs is confirmed with several binary and ternary active layers, affording efficiencies up to 19.01%. Notably, over 98% of the optimal efficiency is maintained as the thickness of the interlayers increases to 40 nm with good reproducibility.