Interfaces play a crucial role in semiconductor devices, but in many device architectures they are nanostructured, disordered and buried away from the surface of the sample. Conventional optical, X-ray and photoelectron probes often fail to provide interface-specific information in such systems. Here we develop an all-optical time-resolved method to probe the local energetic landscape and electronic dynamics at such interfaces, based on the Stark effect caused by electron–hole pairs photo-generated across the interface. Using this method, we found that the electronically active sites at the polymer/fullerene interfaces in model bulk-heterojunction blends fall within the low-energy tail of the absorption spectrum. This suggests that these sites are highly ordered compared with the bulk of the polymer film, leading to large wavefunction delocalization and low site energies. We also detected a 100 fs migration of holes from higher- to lower-energy sites, consistent with these charges moving ballistically into more ordered polymer regions. This ultrafast charge motion may be key to separating electron–hole pairs into free charges against the Coulomb interaction.

接口在半导体设备中起着至关重要的作用，但是在许多设备体系结构中，它们是纳米结构的，无序的并且被埋在远离样品表面的地方。常规的光学，X射线和光电子探针通常无法在此类系统中提供特定于接口的信息。在此，我们基于由跨界面光生电子空穴对引起的斯塔克效应，开发了一种全光时间分辨方法，以探测此类界面处的局部高能态势和电子动力学。使用这种方法，我们发现模型体-异质结共混物中聚合物/富勒烯界面处的电子活性位点在吸收光谱的低能尾部内。这表明，与大部分聚合物薄膜相比，这些部位是高度有序的，导致大波函数离域和低位能。我们还检测到空穴从高能位置向低能位置迁移了100 fs，这与这些电荷弹道地移动到更有序的聚合物区域一致。这种超快的电荷运动可能是将电子-空穴对分离为对抗库仑相互作用的自由电荷的关键。