Highly efficient non-fullerene polymer solar cells from a benzo[1,2-b:4,5-b′]difuran-based conjugated polymer with improved stabilities

Abstract

In this work, a novel benzo[1,2-b:4,5-b′]difuran (BDF)-based polymer (PDiFPBDF-TBz, F13) was designed and synthesized with a wide bandgap of 1.93 eV. With the advantage of electronegative fluorine and furan unit, F13 possessed a deep HOMO level of −5.54 eV, which is favorable for higher V_oc in polymer solar cells (PSCs). When F13 was blended with Y6, the device achieved a PCE of 12.7% with a V_oc of 0.80 V, a J_sc of 22.61 mA cm⁻² and an FF of 70.28%. More surprisingly, the unencapsulated pristine fabricated device generated a higher PCE of up to 13.34% after storing it in nitrogen or air. Further studies showed that the unencapsulated device could retain ∼92% of its original PCE even after exposure to air for ∼1150 hours and to nitrogen for ∼1370 hours, indicating quite promising stabilities. This improvement was due to the interfacial interaction of the active layer and anode layer and the stable micromorphological structure of the F13:Y6 film. The F13:Y6 device also exhibited a suppressed energy loss of 0.525 eV, which is one of the lowest among BDF polymer-based NF-PSCs. These results demonstrate that the rational design of the BDF polymer is highly critical in reaching the state-of-the-art photovoltaic performance and long-term stability.