LAUSR

The cell‐to‐module (CTM) efficiency remaining ratio from monolithic device to large‐area module indicates the scalability potential for large‐area organic solar cells (OSCs). Nowadays, the CTM value is still low as the area increases to larger than 100 cm2. In this work, the crucial role of solvent in CTM for printing, which on one side influenced the large area homogeneity due to the ink rheology property, and on the other side impacted phase separation dynamics because of vaporization and crystalline rate is highlighted. The films from TMB show excessive pure phase and printing line defects in vertical the printing direction due to slow volatilization speed and low adhesion, while Tol‐based films present printing line defects along the printing direction due to large surface adhesion are demonstrated. In contrast, the films from non‐halogenated solvent, o‐XY exhibited a suitable phase separation size and excellent large‐area homogeneity. Consequently, the fully printed 1 cm2 FOSCs exhibit an efficiency of 14.81%. Moreover, the FOSCs module with an area of 28–104 cm2 gives an efficiency of over 13%, with a CTM of 0.9. Selecting suitable non‐halogenated solvents to achieve large‐area uniformity and appropriate phase separation morphology in >100 cm2 modules is of great importance for the industrialization of FOSCs.