Exceptionally low charge trapping enables highly efficient organic bulk heterojunction solar cells

Device preparation: PM6:Y6 OSCs were fabricated with an inverted structure of ITO/zinc oxide (ZnO)/PM6:Y6/molybdenum oxide (MoO3)/Ag. The sol-gel based ZnO precursor solution was prepared by dissolving 220mg of zinc acetate dehydrate in 60 μl of ethanolamine and 2 ml of 2-methoxyethanol. The PM6 and Y6 were synthesized according to the methods in the previous work. The ZnO solution was spin-coated at 4000 rpm on the pre-cleaned ITO substrate. Subsequently, the samples were annealed at 150 °C for 20 min in air and then transferred into an N2-filled glove box for spin-coating of the photoactive layers. The PM6:Y6 (1:1.2) layers were deposited from 7 mg ml chlorobenzene/ chloronaphthalene (CN) (99.5:0.5 vol%) solution by spin-coating at 2000 rpm and then annealed at 100 °C for 10 min. Finally, the MoO3 (10 nm) and Ag (100 nm) layers were deposited by thermal evaporation under high vacuum condition through a shadow mask yielding active areas of 0.045 cm in each device.