Towards Fully Roll-to-roll Printable Organic Solar Cells: Optimization of Gravure Printed Electron Transport Layer

For fully roll-to-roll (R2R) printed flexible organic solar cells, mechanical robustness and solvent compatibility of the
interfacial layers with the active layer and top electrodes remain major challenges. In this work, we present an electron
transport layer (ETL) material based on zinc-ion-chelated polyethyleneimine (PEI-Zn) that combines mechanical
robustness, performance and compatibility with roll-to-roll printing. The PEI-Zn formulation is tailored to an industrialscale
gravure printing process by employing ethanol as processing solvent and refining the printing process parameters and
ink formulation. The scalability of the PEI-Zn ETL material and the gravure printing process is demonstrated by R2R
printing of PEI-Zn ETLs over hundreds of meters on flexible substrate. Fully printable non-fullerene organic solar cells
with R2R gravure printed PEI-Zn ETL and PM6:Y12 active layer are fabricated entirely in ambient conditions, retaining a
high fill factor of 65%.