Important role of alloyed polymer acceptor for high efficiency and stable large-area organic photovoltaics

We developed high performance PM6:N3 bulk-heterojunctions by synthesizing polymers as the second acceptor. The acceptor PY-P2 where a biphenyl linker makes the polymer chain to have high dihedral angles forms intricate alloy-like composites in N3 domains whereas stiff polymer chain of PY-T2 exists separated from the acceptor domain. Introduction of PY-P2 results in much longer lifetimes and diffusion lengths of excitons generated in N3 domain of the PM6:N3:PY-P2 blend compared to those of the excitons in PM6:N3 as well as PM6:N3:PY-T2. Consequently, the PM6:N3:PY-P2 based OPV devices show improved exciton dissociation and change transport with reduced charge recombination. The PM6:N3:PY-P2 organic photovoltaic (OPV) devices prepared with blade-coating at 1 cm2 active area achieved efficiency of 15.2% compared with 12.9% of the PM6:N3 control device; whereas, the corresponding OPV device using PY-T2 shows decreased efficiency of 11.7%. OPV mini-module (active area 5.4 cm2) with PY-P2 achieves high efficiency of 14.7% compared with 11.9% of the PM6:N3 devices. Furthermore, the alloyed PY-P2 acceptor effectively improves OPV thermal stability under 85 °C heating for 1000 h, compared with PY-T2 and control devices. We demonstrated importance of the second polymer acceptor for achieving high-performance large-area OPV, which is significantly affected by its chemical structure.