Organic materials are promising candidates for advanced optoelectronics and are used in light-emitting diodes and photovoltaics. However, the underlying mechanisms allowing the formation of excited states responsible for device functionality, such as exciton generation and charge separation, are insufficiently understood. This is partly due to the wide range of existing crystalline polymorphs depending on sample preparation conditions. Here, we determine the linear optical response of thin-film single-crystal perylene samples of distinct polymorphs in transmission and reflection geometries. The sample quality allows for unprecedented high-resolution spectroscopy, which offers an ideal opportunity for judicious comparison between theory and experiment. Excellent agreement with first-principles calculations for the absorption based on the GW plus Bethe–Salpeter equation (GW-BSE) approach of many-body perturbation theory (MBPT) is obtained, from which a clear picture of the low-lying excitations in perylene emerges, including evidence of an exciton–polariton stopband, as well as an assessment of the commonly used Tamm–Dancoff approximation to the GW-BSE approach. Our findings on this well-controlled system can guide understanding and development of advanced molecular solids and functionalization for applications.

中文翻译：

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结晶per中的低态激发态

有机材料是先进光电子技术的有希望的候选者，并用于发光二极管和光伏电池。但是，对于形成负责器件功能（例如激子生成和电荷分离）的激发态的基本机制了解不足。部分原因是取决于样品制备条件的现有多种晶体多晶型物。在这里，我们确定透射和反射几何中不同多晶型的薄膜单晶per样品的线性光学响应。样品质量可实现前所未有的高分辨率光谱，为明智地比较理论和实验提供了理想的机会。基于多体扰动理论（MBPT）的GW加Bethe–Salpeter方程（GW-BSE）方法，与吸收的第一性原理计算极佳地吻合，从而清晰地了解per中的低价激发出现，包括激子-极化子阻带的证据，以及对GW-BSE方法常用的Tamm-Dancoff近似的评估。我们在这个控制良好的系统上的发现可以指导高级分子固体的理解和开发以及应用的功能化。以及对GW-BSE方法常用的Tamm-Dancoff近似的评估。我们在这个控制良好的系统上的发现可以指导高级分子固体的理解和开发以及应用的功能化。以及对GW-BSE方法常用的Tamm-Dancoff近似的评估。我们在这个控制良好的系统上的发现可以指导高级分子固体的理解和开发以及应用的功能化。