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

Abstract

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.

Nonvolatile floating gate organic memory device based on pentacene/CdSe quantum dot heterojuction

“…This implies that an extra energy barrier due to the type II band bending exists at the heterojunction between pentacene and CdSe QD layers when the two layers are directly assembled. 13 Therefore, when the charge carriers are trapped, the charge trapping can last long enough for the operation of memory device quite a long time. Authors to whom correspondence should be addressed.…”

“…Energetically, the coupling of pentacene and CdSe QD layers can form type II band alignment, which results in band bending at the heterojunction. 13 When a sufficiently large electric field is applied (negative V bottom ), holes can tunnel into the valence band of the CdSe QDs from the HOMO level of the nearby pentacene molecules. The extra energy barrier created by the type II band alignment accounts for significantly prolonged hole trapping in CdSe QDs even after the negative V bottom is removed.…”

Direct evidence of type II band alignment in ZnO nanorods/poly(3-hexylthiophene) heterostructures

“…The PL decay time (396 ps) of ZnO/P3HT is obviously much shorter than that of bare P3HT. These observations do provide an indirect evidence for the type II band alignment across ZnO and P3HT interface, 12,13 because the electrons in the lowest unoccupied molecular orbital (LUMO) band of P3HT have an additional channel to flow into the conduction band of ZnO nanorods by charge transfer as shown in the inset of Fig. 2.…”

“…1,5,11 However, scarce investigation has been conducted along the direct observation of type II transition in organic/inorganic hybrid NCs. 12 In this paper, we provide the direct evidence of the optical transition arising from type II band alignment in ZnO/P3HT NCs based on the band bending near the interface. Interestingly, the magnitude of the blue-shift of type II band alignment transition increases as increasing excitation pumping power, which gives us a firm evidence to support our interpretation.…”