AbstractA new polymer acceptor poly{(N,N′‐bis(2‐ethylhexyl)‐1,4,5,8‐naphthalenedicarboximide‐2,6‐diyl)‐alt‐5,5‐(3,3′‐didodecyl‐2,2′‐bifuran)} (NDI‐BFR) made from naphthalenediimide (NDI) and furan‐derived head‐to‐head‐linked 3,3′‐dialkyl‐2,2′‐bifuran (BFR) units is reported in this study. Compared to the benchmark polymer poly(naphthalenediimide‐alt‐bithiophene) (N2200), NDI‐BFR exhibits a larger bathochromic shift of absorption maxima (842 nm) with a much higher absorption coefficient (7.2 × 104 m−1 cm−1), leading to an ultranarrow optical bandgap of 1.26 eV. Such properties ensure good harvesting of solar light from visible to the near‐infrared region in solar cells. Density functional theory calculation reveals that the polymer acceptor NDI‐BFR possesses a higher degree of backbone planarity versus the polymer N2200. The polymer NDI‐BFR exhibits a decent electron mobility of 0.45 cm2 V−1 s−1 in organic thin‐film transistors (OTFTs), and NDI‐BFR‐based all‐polymer solar cells (all‐PSCs) achieve a power conversion efficiency (PCE) of 4.39% with a very small energy loss of 0.45 eV by using the environmentally friendly solvent 1,2,4‐trimethylbenzene. These results demonstrate that incorporating head‐to‐head‐linked BFR units in the polymer backbone can lead to increased planarity of the polymer backbone, reduced optical bandgap, and improved light absorbing. The study offers useful guidelines for constructing n‐type polymers with narrow optical bandgaps.