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 CuInx Ga(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.
Keywords: charge-carrier diffusion length; fullerene liquid crystals; high-efficiency thick-film devices; organic solar cells.
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