A low bandgap polymer based on isoindigo and bis(dialkylthienyl)benzodithiophene for organic photovoltaic applications

Abstract

Abstract A new conjugated polymer PBDTT‐ID based on N ‐alkylated isoindigo (ID) and bis(2,3‐dialkylthienyl)‐substituted benzo[1,2‐ b :4,5‐ b′ ]dithiophene (BDTT) as repeating units was synthesized. It had an optical bandgap of 1.56 eV and a highest occupied molecular orbital (HOMO) energy level of −5.71 eV. The optical, electrochemical, and photovoltaic properties of new polymer were compared with previous reported polymer PBDT‐ID , which was based on bis(alkoxy)‐substituted benzo[1,2‐ b :4,5‐ b′ ]dithiophene. The new polymer displayed lower HOMO energy level and better absorption properties than polymer PBDT‐ID . The solar cells fabricated with PBDTT‐ID /PC 61 BM (1:2, w/w ) blends as active layers exhibited photoresponse in the range of 300–800 nm. A power conversion efficiency of 4.02% and an open circuit voltage ( V oc ) of 0.94 V were achieved in polymer solar cell device based on the new polymer. This was the highest V oc realized among the isoindigo‐based polymers. The relatively high performances of new polymer in solar cell devices were interpreted in terms of material properties and morphologies of polymer/PCBM blends. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013