Synthesis, optical and electrochemical properties new donor-acceptor (D-A) copolymers based on benzo [1,2-b:3,4-b′:6,5-b"] trithiophene donor and different acceptor units: Application as donor for photovoltaic devices

Two new conjugated D-A polymers P3 (PBTT-d-BTT) and P4 (PBTT-d-TPD) based on same benzo[1,2-b:3,4-b':6,5-b ''] trithiophene (BTT) donor and different acceptors monomers 5,8-dibromo-2-dodecanoylbenzo[1,2-b:3,4-b':6,5-b ''] trithiophene (d-BTT), and 1,3-dibromo-5-(2-ethylhexyl)thieno[3,4]pyrrol-4,6-dione (d-TPD) respectively, were synthesized by Stille cross-coupling reaction and characterized by gel permeation chromatography (GPC), H-1 NMR, UV-Vis absorption, thermal analysis and electrochemical cyclic voltammetry (CV) tests. Photovoltaic properties of the polymers were studied by using the polymers as donor and PC71BM as acceptor with a weight ratio of polymer: PC71BM 1:1, 1:2 and 1:2.5. The optimized photovoltaic device was fabricated with an active layer of a blend P3:PC71BM and P4:PC71BM with a blend ratio of 1: 2 showed PCE 3.16% and 2.42%, respectively under illumination of AM 1.5 at 100 mW/cm(2) with solar simulator. The PCE of the device based on P3:PC71BM processed with DIO/o-DCB has been further improved up to 4.64% with J(sc) of 10.52 mA/cm(2) and FF of 0.58 attributed to the increase in crystalline nature of active layer and more balanced charge transport in the device, induced by DIO additive. (C) 2014 Elsevier B.V. All rights reserved.