Department of Materials Science and Engineering, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
J Phys Chem B. 2013 Dec 12;117(49):15866-74. doi: 10.1021/jp408537p. Epub 2013 Oct 14.
Enhancing the dielectric permittivity of organic semiconductors may open new opportunities to control charge generation and recombination dynamics in organic solar cells. The potential to tune the dielectric permittivity of organic semiconductors by doping them with redox inactive salts was explored using a combination of organic synthesis, electrical characterization, and time-resolved infrared spectroscopy. The addition of the salt, LiTFSI (lithium bis(trifluoro-methyl-sulfonyl)imide), to a conjugated polymer specifically designed to incorporate ions into its bulk phase increased the density of holes and enhanced the static dielectric permittivity of the polymer blend by more than an order of magnitude. The frequency and phase dependence of the real dielectric function demonstrates that the increase in dielectric permittivity resulted from dipolar motion of bound ion pairs or clusters of ions. Interestingly, the increases in the hole density and dielectric permittivity were associated with enhancement of the hole mobility by 2 orders of magnitude relative to the undoped polymer. The charge recombination lifetime also increased by an order of magnitude in the blend with a fullerene electron acceptor when ions were added to the polymer. The findings indicate that ion doping enables organic semiconductors with large increases in low frequency dielectric permittivity and that these changes result in improved charge transport and suppressed charge recombination on the microsecond time scale.
提高有机半导体的介电常数可能为控制有机太阳能电池中的电荷产生和复合动力学开辟新的机会。通过用氧化还原非活性盐掺杂来调节有机半导体的介电常数的潜力，使用有机合成、电特性和时间分辨红外光谱学的组合进行了探索。将盐 LiTFSI（双（三氟甲基磺酰基）亚胺锂）添加到专门设计为将离子掺入其本体相的共轭聚合物中，增加了空穴密度，并将聚合物共混物的静态介电常数提高了一个数量级以上。实介电函数的频率和相位依赖性表明，介电常数的增加是由于束缚离子对或离子簇的偶极子运动引起的。有趣的是，与未掺杂的聚合物相比，空穴密度和介电常数的增加与空穴迁移率提高了 2 个数量级相关。当向聚合物中添加离子时，与富勒烯电子受体的共混物中的电荷复合寿命也提高了一个数量级。研究结果表明，离子掺杂使有机半导体的低频介电常数大大提高，并且这些变化导致在微秒时间尺度上改善了电荷输运并抑制了电荷复合。
