We　investigate　how　the　acceptor-rich　domain　influences　the　microstructure　and　photoluminescence　properties,　and　consequently　the　external　quantum　efficiency　of　photovoltaic　diodes　based　on　blend　films　of　poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(N,N＇-diphenyl)-N,N＇di(p-butyl-oxy-pheyl)-1,4-diaminobenzene)]　(PFB)　and　poly[9,9-dioctylfluorenyl-2,7-diyl)-co-1,4-benzo-{2,10-3}-thiadiazole)]　(F8BT).　We　find　that　the　interfacial　area　depends　strongly　on　the　size　and　density　of　acceptor-or　F8BT-rich　domains　in　the　phase-separation　scheme.　There　exists　an　optimized　density　and　size　distribution　of　the　F8BT-rich　domains,　which　favors　spatial　charge　dissociation.　Meanwhile,　the　balance　of　charge　percolation　between　the　donor(PFB)-and　acceptor(F8BT)-rich　domains　also　plays　important　roles　in　charge　extraction　and　collection.　(C)　2013　Elsevier　B.　V.　All　rights　reserved.