Layer-by-layer　(LBL)　process　has　emerged　as　a　promising　method　in　the　advancement　of　organic　photovoltaics,　emphasizing　scalability　and　reproducibility.　More　importantly,　it　provides　enhanced　morphological　control　for　boosting　carrier　mobility　(mu)　and　power　conversion　efficiency.　By　employing　a　multiscale　approach　that　combined　first-principles　calculations,　molecular　dynamics　simulations,　and　kinetic　Monte　Carlo　methods,　the　relationship　between　LBL　morphology　engineering　and　carrier　mobility　in　donor/acceptor　(PM6/L8-BO)　thin　films　is　elucidated.　During　solvent　evaporation,　the　order　of　solid-phase　formation　in　LBL　films　was　top　surface,　bottom　region,　and　then　the　middle　region.　The　early　solid　precipitation　from　precursor　solutions　was　acceptor,　resulting　in　a　well-ordered　molecular　arrangement　and　reducing　energy　disorder　of　acceptor　LUMO　levels.　Furthermore,　the　difference　in　energy　disorders　between　the　A/D　blend　region　and　the　pure　A　or　D　domains　enabled　LBL　morphology　engineering　to　balance　electron　and　hole　mobilities,　thereby　mitigating　charge　accumulation　and　recombination.　LBL-manufactured　films　presented　higher　carrier　mobility　(mu(LBL)(e)=mu(LBL)(h)　=1.9x10(-3)cm(2)　V(-1)s(-1))　compared　to　bulk　heterojunction(BHJ)　films　(mu(BHJ)(e)　＞　mu(BHJ)(h)=0.1x10(-3)cm(2)center　dot　V(-1)s(-1)).　These　mechanisms　provided　insights　into　strategies　for　enhancing　charge　extraction　of　photo-generated　charge　carriers　through　LBL　engineering,　driving　the　development　of　efficient　organic　photovoltaic　materials.