Lee Thomas, Sanzogni Audrey V, Burn Paul L, Mark Alan E
School of Chemistry & Molecular Biosciences, The University of Queensland, St. Lucia Campus, Brisbane 4072, Australia.
Centre for Organic Photonics & Electronics, The University of Queensland, St. Lucia Campus, Brisbane 4072, Australia.
ACS Appl Mater Interfaces. 2020 Sep 9;12(36):40548-40557. doi: 10.1021/acsami.0c08454. Epub 2020 Aug 26.
The crucial role played by the solution-vapor interface in determining the growth and morphology of an organic semiconductor thin film formed by solvent evaporation has been examined in atomic detail. Specifically, how the loss of individual solvent molecules from the surface of the solution induces solute assembly has been studied using molecular dynamics simulations. The system consisted of (2-phenylpyridine) (acetylacetonate)iridium(III) [Ir(ppy)(acac)] and 4,4'-(-carbazolyl)-1,1'-biphenyl (CBP) in chloroform at 310 K. The simulations clearly indicate that (a) the system does not undergo uniform phase separation (spinodal decomposition), (b) solute aggregation initiates at the solution-vapor interface, (c) the distribution of solvent in the film is nonhomogeneous, (d) this nonhomogeneous distribution can induce preferential alignment of host molecules, and (e) a portion of the solvent likely remains trapped within the film. The work not only demonstrates the ability to directly model evaporation in atomic detail on the relevant length scales but also shows that atomistic simulations have the potential to shed new light on morphological properties of a wide range of organic semiconductor devices manufactured using solution-processing methods.
溶液-蒸汽界面在决定通过溶剂蒸发形成的有机半导体薄膜的生长和形态方面所起的关键作用已在原子层面进行了详细研究。具体而言，利用分子动力学模拟研究了溶液表面单个溶剂分子的损失如何诱导溶质组装。该体系由（2-苯基吡啶）（乙酰丙酮）铱（III）[Ir(ppy)(acac)]和4,4'-（咔唑基）-1,1'-联苯（CBP）在310 K的氯仿中组成。模拟结果清楚地表明：（a）该体系不会发生均匀相分离（旋节线分解）；（b）溶质聚集在溶液-蒸汽界面处开始；（c）薄膜中溶剂的分布不均匀；（d）这种不均匀分布可诱导主体分子的优先排列；（e）一部分溶剂可能被困在薄膜内。这项工作不仅展示了在相关长度尺度上直接对蒸发进行原子层面建模的能力，还表明原子模拟有潜力为使用溶液处理方法制造的广泛有机半导体器件的形态特性提供新的见解。
