With the continuous breakthrough of the efficiency of organic photovoltaics (OPVs), their practical applications are on the agenda. However, the thickness tolerance and upscaling in recently reported high‐efficiency devices remains challenging. In this work, the multiphase morphology and desired carrier behaviors are realized by utilizing a quaternary strategy. Notably, the exciton separation, carrier mobility, and carrier lifetime are enhanced significantly, the carrier recombination and the energy loss (Eloss) are reduced, thus beneficial for a higher short‐circuit density (JSC), fill factor (FF), and open‐circuit voltage (VOC) of the quaternary system. Moreover, the intermixing‐phase size is optimized, which is favorable for constructing the thick‐film and large‐area devices. Finally, the device with a 110 nm‐thick active layer shows an outstanding power conversion efficiency (PCE) of 19.32% (certified 19.35%). Furthermore, the large‐area (1.05 and 72.25 cm2) devices with 110 nm thickness present PCEs of 18.25% and 12.20%, and the device with a 305 nm‐thick film (0.0473 cm2) delivers a PCE of 17.55%, which are among the highest values reported. The work demonstrates the potential of the quaternary strategy for large‐area and thick‐film OPVs and promotes the practical application of OPVs in the future.