Synthesis and photovoltaic properties of alternating conjugated polymers derived from indolo[3,2-b]carbazole and thiophene/thieno[3,2-b]thiophene-cored benzoselenadiazole

Two alternating narrow band gap (NBG) copolymers derived from 5,11-di(N-9-heptadecanyl)-indolo[3,2-b]carbazole (ICZ) and 4,7-di(thien-2-yl)-2',1',3'-benzoselenadiazole (DSeBT) or 4,7-di(thieno[3,2-b]thien-2-yl)-2',1',3'-benzoselenadiazole (DTSeBT), were synthesized and named PICZ-DSeBT and PICZ-DTSeBT, respectively. The PICZ-DSeBT shows good solubility in common organic solvent, and the PICZ-DTSeBT is soluble in hot o-dichlorobenzene (ODCB) and not good soluble in chloroform, toluene etc. The chemical structure, molecular weight and fundamental physical properties of the copolymers were characterized by H-1 NMR, gel permeation chromatography (GPC), cyclic voltammetry (CV), thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) etc. Potential application of the copolymers to be employed as electron donor material and PC61BM ([6,6]-phenyl-C-61 butyric acid methyl ester) for photovoltaic solar cells (PSCs), were investigated. PSCs based on the blends of PICZ-DSeBT/PC61BM (w: w; 1: 2) or PICZ-DTSeBT/PC61BM (w: w; 1: 2) with devices configuration as ITO/PEDOT: PSS/blend/Al, show the power conversion efficiencies (PCEs) of 1.06% and 1.52%, with the open circuit voltage (V (oc)) of 0.75 V and 0.70 V, short circuit current densities (J (sc)) of 3.45 mA/cm(2) and 5.30 mA/cm(2) under an AM1.5 simulator (100 mW/cm(2)) and the photocurrent response on-set wavelength extending up to 760 nm and 800 nm, respectively. It indicates that the NBG copolymers are viable electron donor materials for PSCs.