The Influence of Oxygen Atoms on Conformation and π-π Stacking of Ladder-Type Donor-Based Polymers and Their Photovoltaic Properties

A novel ladder-type donor pyran-bridged indacenodithiophene (IDTP) is developed by introducing two oxygen atoms into indacenodithiophene unit. IDTP possesses a twisted backbone and leads to facially asymmetric arrangement of side chains, resulting in enhanced local pi-pi stacking of according polymer poly[(5,5,11,11-tetrakis(4-octylphenyl)-5,11-dihydrothieno[2', 3': 5,6] pyrano[3,4-g] thieno[3,2-c]isochromene)-alt-4,7-(5-fluoro-2,1,3-benzothiadiazole)] (PIDTP)-FBT, which shows extended absorption range. Moreover, oxygen atoms render deeper highest occupied molecular orbital (HOMO) levels of poly[indacenodithiophene-alt-4,7-(5-fluoro-2,1,3-benzothiadiazole)] (PIDTP)-FBT compared with PIDT-FBT, therefore bringing a higher open-circuit voltage (V-oc).