Enhancement of charge transfer in thermally-expanded and strain-stabilized TIPS-pentacene thin films
Enhancement of charge transfer in thermally-expanded and strain-stabilized TIPS-pentacene thin films
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DOI：
10.1103/physrevresearch.2.033294
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发表时间：
2020-08-24
影响因子：
4.2
通讯作者：
Headrick, Randall L.
中科院分区：
文献类型：
--
作者：
Li, Yang;Wan, Jing;Headrick, Randall L.
我们提出了一个广泛的研究TIPS-并五苯薄膜的光学和电子性质，利用原位X射线衍射，偏振光谱，从头算密度泛函理论。报道了在25 ℃至140 ℃的温度范围内沉积的薄膜和在冷却至室温后在其沉积的晶格间距处应变稳定的薄膜的分子堆积对性质的影响。各向异性热膨胀导致相邻分子的相对位移，同时保持几乎恒定的堆叠距离。这导致随着温度的升高，吸收光谱发生大的蓝移。与溶液吸收光谱相比，蓝移在很大程度上逆转了室温下的红移。还观察到相对于溶液光谱的前两个电子振动峰的比率的减少。电子和振动效应的这种组合是具有正耦合常数J（CT）的电荷转移激子耦合的特征，其敏感地取决于前沿分子轨道的节点与相邻分子上的节点的对齐。这些效应也与电子和空穴电荷转移积分的符号和大小相关，从密度泛函理论计算的t（e）和t（h）提供额外的证据电荷转移介导的耦合，以及洞察到实验观察到的应变稳定薄膜中的场效应晶体管迁移率的增强的起源。结果表明，方法来提高应变薄膜中的载流子迁移率和电子变化的光学监测。
We present an extensive study of the optical and electronic properties of TIPS-pentacene thin films utilizing in situ x-ray diffraction, polarized optical spectroscopy, and ab initio density functional theory. The influence of molecular packing on the properties are reported for thin films deposited in the temperature range from 25 degrees C to 140 degrees C and for films that are strain stabilized at their as-deposited lattice spacings after cooling to room temperature. Anisotropic thermal expansion causes relative displacement of neighboring molecules while maintaining a nearly constant stacking distance. This leads to a large blueshift in the absorption spectrum as the temperature increases. The blueshift largely reverses a redshift at room temperature compared to the solution absorption spectrum. A reduction in the ratio of the first two vibronic peaks relative to the solution spectrum is also observed. This combination of electronic and vibronic effects is a signature of charge transfer excitonic coupling with a positive coupling constant J(CT), which depends sensitively on the alignment of the nodes of the frontier molecular orbitals with those on neighboring molecules. These effects are also correlated with the sign and magnitude of electron and hole charge transfer integrals t(e) and t(h) calculated from density functional theory that provide additional evidence for charge transfer mediated coupling, as well as insight into the origin of an experimentally observed enhancement of the field-effect transistor mobility in strain-stabilized thin films. The results suggest approaches to improve carrier mobility in strained thin films and for optical monitoring of electronic changes.