Large‐scale fabrication of organic solar cells requires an active layer with high thickness tolerability and the use of environment‐friendly solvents. Thick films with high‐performance can be achieved via a ternary strategy studied herein. The ternary system consists of one polymer donor, one small molecule donor, and one fullerene acceptor. The small molecule enhances the crystallinity and face‐on orientation of the active layer, leading to improved thickness tolerability compared with that of a polymer‐fullerene binary system. An active layer with 270 nm thickness exhibits an average power conversion efficiency (PCE) of 10.78%, while the PCE is less than 8% with such thick film for binary system. Furthermore, large‐area devices are successfully fabricated using polyethylene terephthalate (PET)/Silver gride or indium tin oxide (ITO)‐based transparent flexible substrates. The product shows a high PCE of 8.28% with an area of 1.25 cm² for a single cell and 5.18% for a 20 cm² module. This study demonstrates that ternary organic solar cells exhibit great potential for large‐scale fabrication and future applications.