Direct Observation of Hole Transfer from Semiconducting Polymer to Carbon Nanotubes

Abstract

Carbon nanotubes have been proven to play significant roles in polymer-based solar cells. However, there is intensive debate on whether carbon nanotube behaves as a donor or acceptor in the semiconducting polymer:carbon nanotube composite. In this paper, we report a direct observation via Kelvin probe force microscopy (KPFM) that single walled carbon nanotubes (SWNTs) behave as hole transporting channels in poly(3-hexylthiophene-2,5-diyl) (P3HT)/SWNT heterojunctions. By comparing the surface potential (SP) change of SWNT in dark and under illumination, we observed that electrons are blocked from SWNT while holes are transferred to SWNT. This observation can be well-explained by our proposed band alignment model of P3HT/SWNT heterojunction. The finding is further verified by hole mobility measurement using the space charge limited current (SCLC) method. SCLC results indicate that the existence of small amount of SWNT (wt 0.5%) promotes device hole mobility to around 15-fold, indicating SWNT act as hole transfer channel. Our finding of hole transporting behavior of SWNT in P3HT/SWNT blend will provide a useful guidance for enhancing the performance of polymer solar cells by carbon nanotubes.

Covellite CuS nanocrystals: realizing rapid microwave-assisted synthesis in air and unravelling the disappearance of their plasmon resonance after coupling with carbon nanotubes

“…37,[44][45][46][47][48][49] In some studies such capability of carbon nanotubes is believed to play a pivotal role for facilitating exciton dissociation and constituting charge carrier transport highways. This does not sound creditable if it was plasmonic metal nanostructures that were involved.…”

“…This does not sound creditable if it was plasmonic metal nanostructures that were involved. For example, Lang and Li reported the direct observation of hole transfer from a semiconducting polymer to carbon nanotubes 44 and Nismy et al reported the photoluminescence quenching in composite films made of carbon nanotubes and poly(3-hexylthiophene): [6,6]-phenyl-C 61 -butyric acid methyl ester, arising from hole transfer into carbon nanotubes. Nonetheless, considering usually lower charge carrier density in semiconductor nanostructures, in principle a large intensity drop with charge transfer could be anticipated.…”

Kelvin Probe Force Microscopy in Nanoscience and Nanotechnology

“…It was reported that introducing carbon nanotubes into active layer of OSCs improves the power conversion efficiency [63,64] and possesses high open-circuit voltage [65,66]. Photoinduced holes transported from active layer to SWCNTs was observed using KPFM when SWCNTs fabricated on poly(3-hexylthiophene) (P3HT) film as well as on P3HT and 6,6-phenyl-C61-butyric acid methyl ester (PCBM) blended film [10,67]. SWCNTs were carefully coated on top of P3HT in order to expose both P3HT and SWCNTs (Fig.…”

Simulation study of dielectrophoretic assembly of nanowire between electrode pairs

“…Because of quantum confinement and their unique geometries, nanowires exhibit superior performance in applications such as field-effect-transistors (FETs) (Fan et al 2004), chemical sensors (Ahn et al 2008;Zhang et al 2004), photovoltaic cells (Garnett and Yang 2010;Lan and Li 2013), and optical electronics (Gu et al 2008). Nanowires can be synthesized routinely through different techniques today (Gudiksen et al 2002;Jiang et al 2002;Unalan et al 2008).…”