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

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 higherV(oc)in polymer solar cells (PSCs). When F13 was blended with Y6, the device achieved a PCE of 12.7% with aV(oc)of 0.80 V, aJ(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 similar to 92% of its original PCE even after exposure to air for similar to 1150 hours and to nitrogen for similar to 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.