分子掺杂是提高有机半导体导电性的关键策略。通常,电导率在掺杂增加时显示最大值,之后电导率下降。电导率的这种降低通常归因于形态的不利变化。然而,在最近的模拟工作中,已经表明,高掺杂时的电导率反而受到电子-电子排斥而不是形态的限制,至少对于一些材料组合。根据模拟,这种限制预计会显示在塞贝克系数与载流子密度的关系中:如果载流子-载流子排斥限制了电导率,塞贝克系数将遵循海克公式。这里,测量电导率和塞贝克系数作为一系列n型有机半导体的掺杂的函数。此外,使用金属-绝缘体-半导体二极管测量得到的载流子密度,连接掺杂剂负载和电荷载流子的数量。在高载流子密度下,塞贝克系数确实遵循海克的公式,确认电导率受载流子-载流子排斥而不是形态效应的限制。这项研究表明,有机半导体中跳跃传输的当前模型可能不完整。因此,这项研究为有机半导体的设计提供了新的见解。
Molecular
doping is a key strategy to enhance the electrical conductivity of organic semiconductors. Typically, the electrical conductivity shows a maximum value upon increased
doping, after which the conductivity decreases. This decrease in conductivity is commonly attributed to unfavorable changes in the morphology. However, in recent simulation work, has shown, that the conductivity-at high
doping-is instead limited by electron-electron repulsion rather than by morphology, at least for some material combinations. Based on the simulations, this limitation is expected to show up in the dependence of the Seebeck coefficient versus carrier density: the Seebeck coefficient will follow Heike\'s formula if carrier-carrier repulsion limits the conductivity. Here, the electrical conductivity and Seebeck coefficient are measured as a function of
doping for a series of n-type organic semiconductors. Additionally, the resulting carrier density is measured using metal-insulator-semiconductor diodes, which link dopant loading and the number of charge carriers. At high carrier densities, the Seebeck coefficient indeed follows Heike\'s formula, confirming that the conductivity is limited by carrier-carrier repulsion rather than by morphological effects. This study shows that current models of hopping transport in organic semiconductors may be incomplete. As a result, this study offers novel insights in the design of organic semiconductors.