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 π–π 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).

Two oxygen atoms are inserted into indacenodithiophene (IDT) core structure, generating a novel ladder-type donor unit pyran-bridged IDT (IDTP), which shows a facially asymmetric side chain arrangement, resulting in denser π–π stacking of the corresponding 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). A deeper highest occupied molecular orbital (HOMO) level is also obtained by PIDTP-FBT due to the inductive effect of oxygen atoms, giving higher open circuit voltage in the solar cell devices.

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