Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA.
Nat Mater. 2010 Nov;9(11):938-43. doi: 10.1038/nmat2872. Epub 2010 Oct 10.
Excitons in polycrystalline and disordered films of organic semiconductors have been shown to diffuse over distances of 10-50 nm. Here, using polarization- and wavelength-dependent photoconductivity in the highly ordered organic semiconductor rubrene, we show that the diffusion of triplet excitons in this material occurs over macroscopic distances (2-8 μm), comparable to the light absorption length. Dissociation of these excitons at the surface of the crystal is found to be the main source of photoconductivity in rubrene. In addition, we observe strong photoluminescence quenching and a simultaneous enhancement of photoconductivity when the crystal surface is functionalized with exciton splitters. In combination with time-resolved measurements, these observations strongly suggest that long-lived triplet excitons are indeed generated in molecular crystals by fission of singlets, and these triplets provide a significant contribution to the surface photocurrent generated in organic materials. Our findings indicate that the exciton diffusion bottleneck is not an intrinsic limitation of organic semiconductors.
已证实，有机半导体多晶和无序薄膜中的激子可扩散 10-50nm 的距离。在这里，我们使用高度有序的有机半导体苝中的偏振和波长依赖光电导，表明该材料中三重态激子的扩散发生在宏观距离（2-8μm），与光吸收长度相当。在晶体表面上，激子的离解被发现是苝光电导的主要来源。此外，当晶体表面用激子分裂器官能化时，我们观察到强的光致发光猝灭和光电导的同时增强。与时间分辨测量相结合，这些观察结果强烈表明，长寿命三重态激子确实是通过单重态的裂变在分子晶体中产生的，并且这些三重态对在有机材料中产生的表面光电流有很大的贡献。我们的发现表明，激子扩散瓶颈不是有机半导体的固有限制。
