Branched‐alkyl‐substituted poly(thieno3,4‐cpyrrole‐4,6‐dione‐alt‐3,4‐difluorothiophene) (PTPD2FT) can be used as a polymer acceptor in bulk heterojunction (BHJ) solar cells with a low‐band‐gap polymer donor (PCE10) commonly used with fullerenes. The “all‐polymer” BHJ devices made with PTPD2FT achieve efficiencies of up to 4.4 %. While, to date, most efficient polymer acceptors are based on perylenediimide or naphthalenediimide motifs, our study of PTPD2FT polymers shows that linear, all‐thiophene systems with adequately substituted main chains can also be conducive to efficient BHJ solar cells with polymer donors. Better performance through polymers: Branched‐alkyl‐substituted poly(thieno3,4‐cpyrrole‐4,6‐dione‐alt‐3,4‐difluorothiophenes) (PTPD2FT) can be used as polymer acceptors in bulk heterojunction (BHJ) solar cells, achieving some of the best VOC figures (ca. 1.1 V) reported to date for BHJ devices, and power conversion efficiencies of up to 4.4 %, with a low‐band‐gap polymer donor (PCE10) commonly used with fullerenes. 2DT=2‐decyltetradecyl, 2OD=2‐octyldodecyl, 2HD=2‐hexyldecyl.