Side-chain modification of non-fullerene acceptors for organic solar cells with efficiency over 18%

Three non-fullerene acceptors BTP-OC4, BTP-OC6 and BTP-OC8 with different 4-alkyloxyphenyl side-chains were designed and synthesized through a new synthetic route without organotin reagent. The length of the alkyloxy attached to the benzene ring has no influence on the energy levels and absorption of these small-molecular acceptors. However, the active layer morphology is modulated by the different crystallinity caused by the different chain's length. Among them, the device based on the PM6:BTP-OC6 system exhibited the lowest energy loss of 0.513 eV and the highest power conversion efficiency (PCE) of 17.59%, as well as excellent photo-soaking/thermal/storage stability. Moreover, when Y6 was introduced into PM6:BTP-OC6 to fabricate a ternary device, the PCE was promoted to over 18%. Our results provide a feasible strategy to develop high-performance acceptors through fine tuning the aromatic side chain, which can be easily realized by our reported synthetic route.