Charge transport in lead sulfide quantum dots/phthalocyanines hybrid nanocomposites

Chandana Pal,Lydia Sosa-Vargas,Jesús J Ojeda,Ashwani K Sharma,Andrew N Cammidge,Michael J Cook,Asim K Ray

doi:10.1016/j.orgel.2017.02.014

Abstract

A hybrid composite of non-aggregated lead sulfide (PbS) nanoparticles of average size 5.8 ± 1 nm embedded within a film of an octaalkyl substituted metal-free phthalocyanine (Compound 2) was prepared on interdigitated gold electrodes by mild acidic treatment of newly synthesised octasubstituted lead phthalocyanine analogue (Compound 1) in solid state phase. This nanocomposite film shows an enhancement of in-plane electrical conductivity over that of a film of octaalkyl substituted metal-free phthalocyanine alone by nearly 65%. This observation is consistent with the formation of charge complex compound as indicated by Raman and XPS data. The presence of PbS in the composite was examined on the basis of XRD peak positions which are comparable with those of bulk PbS. A band gap of 2.22 eV was calculated from optical absorption data using Tauc's law, implying quantum confinement. The mono dispersal behaviour of PbS nanoparticles was established from TEM and XRD studies. The hopping conduction mechanism is found to be primarily responsible for charge transport in the hybrid nanocomposite film with the hopping distance larger than PbS diameter.

Highlights

Hybrid materials containing inorganic nanoparticles in organic matrices have generated enormous fundamental research interest in the field of nanoscience because of their potential applications in environmental, optoelectronic, biomedical and energy storage fields [1]
A comparison with the X-ray diffraction (XRD) pattern in Figure 2(c) for the pristine spun film of Compound 2 implies the formation of hybrid nanocomposite films containing PbS quantum dots embedded in the matrix of Compound 2 due to the removal of out-of-plane lead atom from Compound 1 by reaction with H2S
This value is much smaller than its exciton Bohr radius of 18 nm and the threshold size for the quantum confinement is reported to be less than 10 nm for ester capped PbS quantum dots [25]

Summary

Introduction

Hybrid materials containing inorganic nanoparticles in organic matrices have generated enormous fundamental research interest in the field of nanoscience because of their potential applications in environmental, optoelectronic, biomedical and energy storage fields [1]. The out-of-plane Pb atom makes the Pb-N bond weaker and can be removed by a reducing agent like hydrogen sulphide (H2S) gas This property has been exploited in our previous work for one-step, cost-effective solid state synthesis of inorganic/organic hybrid nanocomposites through the displacement of lead from spin-coated thin films of octahexyl substituted discotic liquid crystalline lead phthalocyanine (6PbPc) under an atmosphere of hydrogen sulphide to afford PbS quantum dots embedded in a single layered metal free phthalocyanine matrix. (benzo-15-crown-5)-substituted phthalocyaninato Cd(II) was exploited to form a CdS quantum dots based hybrid /metal-free phthalocyanine [21] This present article presents the results of comprehensive studies on steady state conduction characteristics of the PbS/C8H2Pc nanocomposite on an interdigitated gold electrode system over the temperature range between 87K and 430 K under a vacuum of 10-4 mbar. Optical absorption spectra for spun films on ultrasonically cleaned glass substrates were recorded with a Perkin Elmer LAMBDA 650 UV/Vis spectrophotometer using a 1 cm pathlength cuvette at room temperature with a scanning rate of 654.8 nm/min in the range from 300 nm to 850 nm

Results and discussions

R of the intensities of B1g to

Conclusions