Fullerene‐Liquid‐Crystal‐Induced Micrometer‐Scale Charge‐Carrier Diffusion in Organic Bulk Heterojunction

The short charge‐carrier diffusion length (LD) (100–300 nm) in organic bulk heterojunction (BHJ) impedes the further improvement in power conversion efficiency (PCE) of organic solar cells (OSCs), especially for thick‐film (>400 nm) devices matching with industrial solution processing. Here a facile method is developed to efficiently increase LD and then improve PCEs of OSCs via introducing a fullerene liquid crystal, F1, into the active layer. F1 combines the inherent high electron mobility of fullerene and strong self‐assembly capacity of liquid crystal, providing a fast channel for charge‐carrier transport and reducing energetic disorder and trap density in BHJ film via enhancing crystallization. Typically, in PM6:Y6:F1 BHJ, the enhanced charge‐carrier mobility (>10−2 cm−2 V−1 s−1) and prolonged charge‐carrier lifetime (55.3 µs) are acquired to realize the record LD of 1.6 or 2.4 µm for electron or hole, respectively, which are much higher than those of the PM6:Y6 binary sample and comparable to or even better than those values reported for some inorganic/hybrid materials, such as CuInxGa(1−x)Se2 (CIGS) and perovskite thin films. Benefitting from the micrometer‐scale LD, the PM6:Y6:F1 ternary OSCs sustain a remarkable PCE of 15.23% with the active layer thickness approaching 500 nm. A high‐mobility fullerene liquid crystal is introduced into the active layer of organic solar cells (OSCs) to provide a fast channel for charge‐carrier transport, reduce energetic disorder and trap density via enhancing crystallization, and then realize micrometer‐scale charge‐carrier diffusion, leading to the impressive power conversion efficiencies of 15.23% for OSCs with the thickness approaching 500 nm.