A novel narrow-band-gap conjugated polymer with heterocyclic backbone, poly[4,7-bis(4-decanyl-2-thienyl)-, 2',1',3 -benzothiadiazole-thiophene-2,5-] (PDDBT, E-g = 1.38 eV) was synthesized by a Stille coupling reaction. Prototype bulk heterojunction photovoltaic cells from PDDBT and [6,6]-phenyl-C-61 -butyric acid methyl ester (PCBM) with a ITO/ PEDOT:PSS/PDDBT:PCBM(1:3)/Ba/Al device, architecture showed power conversion efficiencies up to 0.13% under AM1.5 solar simulator (100 mW . cm(-2)) with an open-circuit voltage V-oc of 0.65 V, a short-circuit current density J(sc) of 0.6 mA . cm(-2), and a photocurrent response up to 880 nm. The electroluminescent device from PDDBT showed a near-infrared fight emission peak at around 830 ran with maximal external quantum efficiency of 0.08% and a turn-on voltage at 3.5 V.