Modulating the molecular packing and distribution enables fullerene-free ternary organic solar cells with high efficiency and long shelf-life

Abstract

The main-chain planar configuration is a popular design principle for nonfullerene acceptors (NFAs), while the too flat backbones enable NFAs suffer from intense aggregations and form large crystalline domains, which will result in poor device efficiency and inferior stability. This effect is reflected particularly serious in near-infrared NFAs. To relieve the negative impact of the inherent nature, an efficient ternary strategy, which introducing hydrogen-bond between the third component and NFA, is utilized to modulate the crystallization and packing properties of the acceptors. Here, IEICO-4F is chosen as a typical NFA for its nearly planar main-chain structure. A high efficiency of 13.53% with a decent fill factor (FF) of 71.36% are recorded in PTB7-Th:IEICO-4F:DIBC containing ternary organic solar cells (OSCs), which is superior to the binary OSC (efficiency of 11.71%, FF of 65.29%). It is noteworthy that after 90 days of storage in ambient condition, the efficiency also maintains at 85.02% of the primitive state, while that of the binary device falls to 44.38%. Film morphology and charge dynamics analysises demonstrate that the high performance of the ternary OSC originates from the hydrogen-bond optimized molecular crystallization, stacking and distribution. Furthermore, similar conclusions can be obtained in another NFA system PBDB-TF:Y6 to yield a champion efficiency of 16.41%. These results prove that intermolecular hydrogen-bond strategy is an effective and convenient approach to optimize the micromorphology of NFAs and fabricate high performance NFA OSCs.