Abstract
Based on first-principles calculations, the relationship between molecular packing and charge-transport parameters has been investigated and analysed in detail. It is found that the crystal packing forces in the flexible organic molecule 4-(1,2,2-triphenylvinyl)-aniline salicylaldehyde hydrazone (A) can apparently overcome the dynamic intramolecular rotations and the intramolecular steric repulsion, effectively enhancing the molecular rigidity and decreasing the internal reorganization energy. The conducting properties of A have also been simulated within the framework of hopping models, and the calculation results show that the intrinsic electron mobility in A is much higher than the corresponding intrinsic hole mobility. These theoretical investigations provide guidance for the efficient and targeted control of the molecular packing and charge-transport properties of organic small-molecule semiconductors and conjugated polymeric materials.
Highlights
Charge transport in organic materials is one of the most important properties in the performance of solar cells, organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), batteries and sensors (Root et al, 2017; Shirota & Kageyama, 2007; Wang et al, 2012)
Since the 1950s, significant progress has been made towards improved understanding of intrinsic charge-transport phenomena in organic materials, and several models, such as the band model, the tight-binding model and the hopping model, have been proposed for the simulation and prediction of low-density intrinsic transport behaviour in organic crystals observed in OFET experiments (Grozema & Siebbeles, 2008; Shuai et al, 2011)
For most organic crystal materials, the hopping model is appropriate to describe carrier transport properties, especially at room temperature, due to the fact that organic molecules are usually aggregated by weak van der Waals forces and the intermolecular electronic couplings are much weaker than the electron-vibration couplings for the majority of conjugated organic oligomers (Shuai et al, 2014)
Summary
Charge transport in organic materials is one of the most important properties in the performance of solar cells, organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), batteries and sensors (Root et al, 2017; Shirota & Kageyama, 2007; Wang et al, 2012). Intermolecular interactions are neglected in the evaluation of reorganization energy, and the calculated reorganization energy in the gas phase is usually adopted in the simulation of anisotropic mobility in organic materials (Deng et al, 2015). Rigid molecules undergo small geometric relaxations during the charge-transfer process, and their calculated reorganization energy is less affected by the surroundings. 696 Huipeng Ma et al Packing-induced molecular hardening and relative positions of the interacting units is addressed in detail Based on these quantum-chemistry calculation results, combined with the Marcus–Hush electron-transfer theory, we simulated the anisotropic electron and hole mobilities of A and provide here an assessment of its field-effect properties as a potential p-type, n-type or ambipolar organic semiconducting material
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