We report all-polymer solar cells (All-PSCs) with record-high power conversion efficiency (PCE) through tuning the molecular weights of the polymer donor (PBDB-T) to form optimal active layer morphology.By combining the polymer donors with a newly reported polymer acceptor (PJ 1),an unprecedented high PCE of 15.4％ and fill factor over 75％ were achieved for the All-PSCs with the medium molecular weight polymer donor (PBDB-TMW),which is the highest value for All-PSCs reported so far.Detailed morphology investigation revealed that the proper phase separation in the PBDB-TMW:PJ 1 blend should account for the superior device performance as PBDB-TMW exhibits appropriate miscibility with the polymer acceptor P J1.These results demonstrated that the device performance of All-PSCs could be fully comparable to that of small molecular acceptor-based PSCs.The formation of optimized morphology via precise control of molecular weights of polymer donors and acceptors is crucial to achieve this goal.