An Extremely Narrow‐Band‐Gap Conjugated Polymer with Heterocyclic Backbone and its Use in Optoelectronic Devices

Summary: 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 light emission peak at around 830 nm with maximal external quantum efficiency of 0.08% and a turn‐on voltage at 3.5 V.Normalized PL and EL spectra of PDDBT and photosensitivity of PVCs based on PDDBT/PCBM (1:3) blend. The scheme shows the chemical structure of PDDBT.