Rahmanudin Aiman, Yao Liang, Jeanbourquin Xavier A, Liu Yongpeng, Sekar Arvindh, Ripaud Emilie, Sivula Kevin
Laboratory for Molecular Engineering of Optoelectronic Nanomaterials , Ecole Polytechnique Fédérale de Lausanne , Station 6 , CH-1015 , Switzerland . Email:
Green Chem. 2018 May 21;20(10):2218-2224. doi: 10.1039/c8gc00335a. Epub 2018 Apr 17.
Melt-processing of organic semiconductors (OSCs) is a promising environmentally-friendly technique that can alleviate dependence on toxic chlorinated solvents. While melt-processed single-component OSC devices ( field-effect-transistors) have been demonstrated, multi-component bulk heterojunctions (BHJs) for organic photovoltaics (OPVs) remain a challenge. Herein, we demonstrate a strategy that affords tunable BHJ phase segregation and domain sizes from a single-phase homogeneous melt by employing strongly-crystalline small-molecule OSCs together with a customized molecular compatibilizing (MCP) additive. An optimized photoactive BHJ with 50 wt% MCP achieved a device power conversion efficiency of 1% after melting the active layer at 240 °C (15 min, followed by slow cooling) before deposition of the top electrode. BHJ morphology characterization using atomic force and Kelvin probe microscopy, X-ray diffraction, and photo-luminescence measurements further demonstrate the trade-off between free charge generation and transport with respect to MCP loading in the BHJ. In addition, a functional OPV was also obtained from the melt-processing of dispersed micron-sized solid BHJ particles into a smooth and homogeneous thin-film by using the MCP approach. These results demonstrate that molecular compatibilization is a key prerequisite for further developments towards true solvent-free melt-processed BHJ OPV systems.
有机半导体（OSCs）的熔融加工是一种很有前景的环保技术，它可以减轻对有毒氯化溶剂的依赖。虽然已经展示了熔融加工的单组分OSC器件（场效应晶体管），但用于有机光伏（OPV）的多组分本体异质结（BHJs）仍然是一个挑战。在此，我们展示了一种策略，通过将强结晶小分子OSCs与定制的分子相容剂（MCP）添加剂一起使用，从单相均匀熔体中实现可调谐的BHJ相分离和畴尺寸。在沉积顶电极之前，在240°C（15分钟，随后缓慢冷却）下将活性层熔融后，含50 wt% MCP的优化光活性BHJ实现了1%的器件功率转换效率。使用原子力显微镜和开尔文探针显微镜、X射线衍射以及光致发光测量对BHJ形态进行表征，进一步证明了在BHJ中自由电荷产生和传输与MCP负载之间的权衡。此外，通过使用MCP方法，将分散的微米级固体BHJ颗粒熔融加工成光滑均匀的薄膜，还获得了功能性OPV。这些结果表明，分子相容化是朝着真正无溶剂熔融加工的BHJ OPV系统进一步发展的关键先决条件。
