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 theinterfacial layers with the active layer and top electrodes remain major challenges. In this work, we present an electrontransport layer (ETL) material based on zinc-ion-chelated polyethyleneimine (PEI-Zn) that combines mechanicalrobustness, performance and compatibility with roll-to-roll printing. The PEI-Zn formulation is tailored to an industrialscalegravure printing process by employing ethanol as processing solvent and refining the printing process parameters andink formulation. The scalability of the PEI-Zn ETL material and the gravure printing process is demonstrated by R2Rprinting of PEI-Zn ETLs over hundreds of meters on flexible substrate. Fully printable non-fullerene organic solar cellswith R2R gravure printed PEI-Zn ETL and PM6:Y12 active layer are fabricated entirely in ambient conditions, retaining ahigh fill factor of 65%.