Synthesis and characterization of novel indacenodithiophene-based narrow band-gap polymers with pendant isoindigo units for polymer solar cells

Two novel indacenodithiophene (IDT) based donor-acceptor (D-A) narrow band-gap polymers PIDTBDTID and PIDTBDT(ID)2 were designed and synthesized, where one/two isoindigo (ID) moieties were introduced into the backbone as the acceptor unit. The PIDTBDTID containing one ID unit exhibited better light-harvesting properties and charge transport properties. On the other hand, the PIDTBDT(ID)2 with two ID units displayed lower the highest occupied molecular orbital energy levels (HOMO). Using these polymers as electron donors and PC71BM as electron acceptor, polymer solar cells based on PIDTBDTID exhibited better photovoltaic performance with a power conversion efficiency (PCE) of 2.66%, an open-circuit voltage (VOC) of 0.87 V and an enhanced short-circuit current (JSC) of 7.24 mA cm−2. While the PIDTBDT(ID)2-based PSCs shown a PCE of 2.50%, an improved VOC of 0.93 V and an JSC of 6.34 mA cm−2.121