The energy band structure provides crucial information on charge transport behaviour in organic semiconductors, such as effective mass, transfer integrals and electron–phonon coupling. Despite the discovery of the valence (the highest occupied molecular orbital (HOMO)) band structure in the 1990s, the conduction band (the lowest unoccupied molecular orbital (LUMO)) has not been experimentally observed. Here we employ angle-resolved low-energy inverse photoelectron spectroscopy to reveal the LUMO band structure of pentacene, a prototypical high-mobility organic semiconductor. The derived transfer integrals and bandwidths from the LUMO are substantially smaller than those predicted by density functional theory calculations. To reproduce this bandwidth reduction, we propose an improved (partially dressed) polaron model that accounts for the electron–intramolecular vibrational interaction with frequency-dependent coupling constants based on Debye relaxation. This model quantitatively reproduces not only the transfer integrals, but also the temperature-dependent HOMO and LUMO bandwidths, and the hole and electron mobilities. The present results demonstrate that electron mobility in high-mobility organic semiconductors is indeed limited by polaron formation.

能带结构提供了有关有机半导体中电荷传输行为的关键信息，例如有效质量、转移积分和电子-声子耦合。尽管在 1990 年代发现了价带（最高占据分子轨道 (HOMO)）带结构，但尚未通过实验观察到导带（最低未占据分子轨道 (LUMO)）。在这里，我们采用角分辨低能逆光电子能谱来揭示原型高迁移率有机半导体并五苯的 LUMO 能带结构。从 LUMO 导出的传输积分和带宽远小于密度泛函理论计算预测的值。为了重现这种带宽减少，我们提出了一种改进的（部分修饰的）极化子模型，该模型解释了电子 - 分子内振动相互作用与基于德拜松弛的频率相关耦合常数。该模型不仅定量地再现了转移积分，还定量地再现了与温度相关的 HOMO 和 LUMO 带宽，以及空穴和电子迁移率。目前的结果表明，高迁移率有机半导体中的电子迁移率确实受到极化子形成的限制。