Quan Li, Lee Stephanie S, Kalyon Dilhan M
Chemical Engineering and Materials Science, Stevens Institute of Technology, Castle Point St., Hoboken, NJ 07030, USA.
Soft Matter. 2021 Feb 19;17(6):1642-1654. doi: 10.1039/d0sm01759k.
Organic solar cells (OSCs) containing an active layer consisting of a nanostructured blend of a conjugated polymer like poly(3-hexylthiophene) (P3HT) and an electron acceptor have the potential of competing against silicon-based photovoltaic panels. However, this potential is largely unfulfilled first due to interrelated production and stability issues of organic solar cells and second due to the unscalable nature of the generally employed spin coating process used for the fabrication of organic solar cells. Furthermore, alternatives to spin coating, especially relying on continuous polymer processing methods like extrusion and coating, cannot be readily applied due to the typically low shear viscosity and elasticity of polymer solutions making up the active layer. Recently, He et al. have reported that the gelation of P3HT with [6,6]-phenyl-C61-butyric acid methyl ester (PC60BM) under sub-ambient conditions can provide a new route to the processing of the active layers of bulk heterojunction solar cells. Furthermore, increases in power conversion efficiencies (PCEs) of the P3HT/PC60BM active layer were determined to be possible under certain shearing and thermal histories of the P3HT/PC60BM gels. Here oscillatory and steady torsional flows were used to investigate the gel formation dynamics of P3HT with a recently proposed non-fullerene acceptor o-IDTBR under sub-ambient conditions and compared with the gelation behavior of P3HT/PC60BM blends. The rheological material functions as well as the gel strengths defined on the basis of linear viscoelastic material functions, characterized via small-amplitude oscillatory shearing, were observed to be functions of the P3HT and o-IDTBR concentrations, the solvent used and the shearing conditions. Overall, the P3HT gels which formed upon quenching to sub-zero temperatures were found to be stable during small-amplitude oscillatory shear (linear viscoelastic range) but broke down even at the relatively low shear rates associated with steady torsional flows, suggesting that the shearing conditions used during the processing of gels of P3HT and blends of P3HT with small molecule acceptors can alter the gel structure, possibly leading to changes in the resulting active layer performance.
有机太阳能电池（OSC）包含一个活性层，该活性层由共轭聚合物（如聚（3 - 己基噻吩）（P3HT））与电子受体的纳米结构共混物组成，具有与硅基光伏板竞争的潜力。然而，这种潜力在很大程度上尚未实现，首先是由于有机太阳能电池相关的生产和稳定性问题，其次是由于用于制造有机太阳能电池的通常采用的旋涂工艺不可扩展。此外，由于构成活性层的聚合物溶液通常具有低剪切粘度和弹性，旋涂的替代方法，特别是依赖于连续聚合物加工方法（如挤出和涂层），不能轻易应用。最近，He等人报道，在低于环境温度的条件下，P3HT与[6,6] - 苯基 - C61 - 丁酸甲酯（PC60BM）的凝胶化可以为体异质结太阳能电池活性层的加工提供一条新途径。此外，在P3HT/PC60BM凝胶的某些剪切和热历史条件下，确定P3HT/PC60BM活性层的功率转换效率（PCE）有可能提高。在此，使用振荡和稳态扭转流动来研究P3HT与最近提出的非富勒烯受体o - IDTBR在低于环境温度的条件下的凝胶形成动力学，并与P3HT/PC60BM共混物的凝胶化行为进行比较。通过小振幅振荡剪切表征的流变材料函数以及基于线性粘弹性材料函数定义的凝胶强度，被观察到是P3HT和o - IDTBR浓度、所用溶剂和剪切条件的函数。总体而言，淬火至零下温度时形成的P3HT凝胶在小振幅振荡剪切（线性粘弹性范围）期间被发现是稳定的，但即使在与稳态扭转流动相关的相对较低剪切速率下也会分解，这表明在P3HT凝胶以及P3HT与小分子受体的共混物加工过程中使用的剪切条件可以改变凝胶结构，可能导致所得活性层性能的变化。
