Fullerene‐Liquid‐Crystal‐Induced Micrometer‐Scale Charge‐Carrier Diffusion in Organic Bulk Heterojunction
Fuwen Zhao, Dan He, Can Zou, Yawen Li, Ke Wang, Jianqi Zhang, Shuang Yang, Yingfeng Tu, Chunru Wang, Yuze Lin
Abstract
Abstract The short charge‐carrier diffusion length ( L D ) (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 L D 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 L D 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 CuIn x Ga (1− x ) Se 2 (CIGS) and perovskite thin films. Benefitting from the micrometer‐scale L D , the PM6:Y6:F1 ternary OSCs sustain a remarkable PCE of 15.23% with the active layer thickness approaching 500 nm.