Band Structure Engineering in Organic Semiconductors

能带结构工程，即通过混合不同的元素来“调节”半导体的能带能量的可能性，是现代电子学和光电子学的一项关键技术。在有机半导体中，这种方法似乎是不可能的，因为它需要离域电子态--这种情况通常不会在与器件应用相关的多晶或非晶态有机薄膜中观察到。然而，我们最近做了一个令人惊讶的观察，即通过混合分子取代基来调节有机半导体中的电子能量仍然是可能的：由于分子的四极矩而产生的长程库仑相互作用平均能量。这为应用开辟了新的前景，如微调有机太阳能电池的开路电压或有机发光二极管(OLED)的发射波长，或控制触点的注入特性。在这个项目中，我们想要远远超越最初的观察：我们想要解决关键的开放问题，如局部形态和能量结构之间的详细相互作用，分子偶极矩对电子能量的影响，远距离相互作用对最高占据轨道以外的能级的影响，等等。同时，该项目还解决了首批申请问题。

Band structure engineering, i.e., the possibility to "tune" the band energies of semiconductors by mixing different elements, is a key technology for modern electronics and optoelectronics. In organic semiconductors, this approach seemed to be impossible since it requires delocalized electronic states - a situation which usually is not being observed in polycrystalline or amorphous organic thin films which are relevant for device applications. However, we have recently made the surprising observation that it is nevertheless possible to tune electronic energies in organic semiconductors by mixing molecular substituents: Long-range Coulomb interactions due to quadrupole moments of the molecules average the energies. This opens promising new perspectives for applications, such as the fine-tuning of open-circuit voltages in organic solar cells or emission wave lengths in organic light emitting diodes (OLED), or controlling the injection properties at contacts. In this project, we want to go far beyond the initial observations: We want to address key open questions, like the detailed interplay between local morphology and energy structure, the impact of molecular dipole moments on electronic energies, the effect of long-range interactions on energy level beyond the highest occupied orbitals, and many more. In parallel, the project also addresses first applications.