Walter Lisa S, Axt Amelie, Borchert James W, Kammerbauer Theresa, Winterer Felix, Lenz Jakob, Weber Stefan A L, Weitz R Thomas
Faculty of Physics, Ludwig-Maximilians-Universität München, 80539, Munich, Germany.
I. Institute of Physics, Georg-August-Universität Göttingen, 37077, Göttingen, Germany.
Small. 2022 Aug;18(34):e2200605. doi: 10.1002/smll.202200605. Epub 2022 Jul 29.
In organic electronics, local crystalline order is of critical importance for the charge transport. Grain boundaries between molecularly ordered domains are generally known to hamper or completely suppress charge transfer and detailed knowledge of the local electronic nature is critical for future minimization of such malicious defects. However, grain boundaries are typically hidden within the bulk film and consequently escape observation or investigation. Here, a minimal model system in form of monolayer-thin films with sub-nm roughness of a prototypical n-type organic semiconductor is presented. Since these films consist of large crystalline areas, the detailed energy landscape at single grain boundaries can be studied using Kelvin probe force microscopy. By controlling the charge-carrier density in the films electrostatically, the impact of the grain boundaries on charge transport in organic devices is modeled. First, two distinct types of grain boundaries are identified, namely energetic barriers and valleys, which can coexist within the same thin film. Their absolute height is found to be especially pronounced at charge-carrier densities below 10 cm -the regime at which organic solar cells and light emitting diodes typically operate. Finally, processing conditions by which the type or energetic height of grain boundaries can be controlled are identified.
在有机电子学中，局部晶体有序对于电荷传输至关重要。分子有序域之间的晶界通常会阻碍或完全抑制电荷转移，而对局部电子性质的详细了解对于未来最小化此类有害缺陷至关重要。然而，晶界通常隐藏在体膜内部，因此难以被观察或研究。在此，我们展示了一种最小模型系统，它是具有亚纳米粗糙度的原型n型有机半导体的单层薄膜形式。由于这些薄膜由大的晶体区域组成，因此可以使用开尔文探针力显微镜研究单个晶界处的详细能量景观。通过静电控制薄膜中的电荷载流子密度，对晶界对有机器件中电荷传输的影响进行建模。首先，识别出两种不同类型的晶界，即能量势垒和势谷，它们可以共存于同一薄膜中。发现在电荷载流子密度低于10 cm⁻³（有机太阳能电池和发光二极管通常运行的区域）时，它们的绝对高度尤为明显。最后，确定了可以控制晶界类型或能量高度的加工条件。
