Development　of　n-type　polymer　semiconductor　materials　for　all-polymer　solar　cells　(all-PSCs)　receives　increasingly　attention.　A　series　of　new　n-type　random　terpolymers　with　identical　perylene　diimide-thiophene　alternating　copolymer　backbone　and　different　composition　of　the　side　chains　2-octyldodecanyl　and　2-ethylhexanyl　have　been　designed　and　applied　as　the　acceptor　materials　in　all-PSCs.　The　all-PSCs　based　on　bulk　heterojunction　blends　with　side-chain　engineered　random　terpolymer　P(1/1)　as　acceptor　and　PTB7-Th　as　donor　give　a　high　power　conversion　efficiency　value　of　6.18%　with　an　open-circuit　voltage　of　0.74　V,　a　short-circuit　current　density　of　14.71　mA　cm−2,　and　a　fill　factor　of　0.57.　The　results　demonstrate　that　design　of　the　poly(perylenediimide-alt-thiophene)　random　terpolymer　acceptors　via　side-chain　engineering　is　an　alternative　strategy　for　obtaining　high-performance　photovoltaic　acceptor　materials.　©　2020