Direct evidence of type II band alignment in nanoscale P3HT/CdSe heterostructures

Due to inherent advantages of both constituent materials, organic/inorganic hybrid composites have attracted increasing attention. One of the fundamental issues needed to be resolved is their band alignment, which governs most of the electrical and optical properties. Here, we report the investigation of optical transition in poly(3-hexylthiophene) (P3HT)/CdSe nano-composites (NCs). It is found that the relaxation dynamics of photo-carriers in NCs is dominated by charge separation effects. Based on the band bending effect and the quantum confinement energy of electrons in the conduction band of CdSe quantum dots, we provide direct evidence of type II band alignment in P3HT/CdSe NCs. The establishment of a type II transition in NCs is very useful for the future design of efficient optoelectronic devices based on conjugated polymer/semiconductor hybrid systems.