All-polymer　solar　cells　(APSCs),　composed　of　semiconducting　donor　and　acceptor　polymers,　have　attracted　considerable　attention　due　to　their　unique　advantages　compared　to　polymer-fullerene-based　devices　in　terms　of　enhanced　light　absorption　and　morphological　stability.　To　improve　the　performance　of　APSCs,　the　morphology　of　the　active　layer　must　be　optimized.　By　employing　a　random　copolymerization　strategy　to　control　the　regularity　of　the　backbone　of　the　donor　polymers　(PTAZ-TPDx)　and　acceptor　polymers　(PNDI-Tx)　the　morphology　can　be　systematically　optimized　by　tuning　the　polymer　packing　and　crystallinity.　To　minimize　effects　of　molecular　weight,　both　donor　and　acceptor　polymers　have　number-average　molecular　weights　in　narrow　ranges.　Experimental　and　coarse-grained　modeling　results　disclose　that　systematic　backbone　engineering　greatly　affects　the　polymer　crystallinity　and　ultimately　the　phase　separation　and　morphology　of　the　all-polymer　blends.　Decreasing　the　backbone　regularity　of　either　the　donor　or　the　acceptor　polymer　reduces　the　local　crystallinity　of　the　individual　phase　in　blend　films,　affording　reduced　short-circuit　current　densities　and　fill　factors.　This　two-dimensional　crystallinity　optimization　strategy　locates　a　PCE　maximum　at　highest　crystallinity　for　both　donor　and　acceptor　polymers.　Overall,　this　study　demonstrates　that　proper　control　of　both　donor　and　acceptor　polymer　crystallinity　simultaneously　is　essential　to　optimize　APSC　performance.