Ternary
bulk-heterojunction (BHJ) polymer solar cells (PSCs) have
been proved to show superior performance over binary BHJ PSCs. In
this concise contribution, an octyl-substituted indacenodithieno[3,2-b] thiophene-based nonfullerene acceptor (O-ITIC), which
is a derivative of ITIC but presents lower electron affinity, narrower
optical band gap, and improved propensity to crystallize, is incorporated
as a third component in the state-of-the-art PM6:Y6 binary BHJ blends
to fabricate ternary BHJ solar cells. Results show that the optimized
PM6:Y6:O-ITIC-based ternary BHJ solar cells reach higher power conversion
efficiency (PCE) of 16.5% than that achieved in PM6:Y6- and PM6:O-ITIC-based
binary solar cells with PCEs of 15.8 and 11.1%, respectively. Well-mixed
acceptors phases and crystallite with a favorable face-on orientation
are concurrently formed in the optimized ternary BHJ films. Consequently,
more efficient exciton dissociation, improved and balanced charge
transportation and extraction, and suppressed charge recombination
losses occur in the optimized ternary BHJ devices with the aid of
the third component O-ITIC. As a result, the optimized ternary devices
demonstrate the lowest energy loss of 0.51 eV, an improved fill factor
of 74.7%, and thus the highest PCE of 16.5%. This systematic study
makes clear that rationally designed guest acceptors not only can
provide additional channels for photon absorption and exciton dissociation
but also can offer an effective strategy in tailoring the BHJ nanoscale
morphology that are prerequisites for fast charge transportation,
efficient charge extraction, and thus promising polymer solar cells.