Abstract
Electrophoretic deposition (EPD) is an emerging technique in nanomaterial-based device fabrication. Here, we report an in-depth study of this approach as a means to deposit colloidal quantum dots (CQDs), in a range of solvents. For the first time, we report the significant improvement of EPD performance via the use of dichloromethane (DCM) for deposition of CQDs, producing a corresponding CQD-TiO2 composite with a near 10-fold increase in quantum dot loading relative to more commonly used solvents such as chloroform or toluene. We propose this effect is due to the higher dielectric constant of the solvent relative to more commonly used and therefore the stronger effect of EPD in this medium, though there remains the possibility that changes in zeta potential may also play an important role. In addition, this solvent choice enables the true universality of QD EPD to be demonstrated, via the sensitization of porous TiO2 electrodes with a range of ligand capped CdSe QDs and a range of group II-VI CQDs including CdS, CdSe/CdS, CdS/CdSe and CdTe/CdSe, and group IV-VI PbS QDs.
Highlights
Electrophoretic deposition (EPD) is a relatively new technique finding application in the field of nanotechnology, despite it having been utilised for a number of years in important areas such as the ceramic industry [1,2]
We show for the first time, the specific effectiveness of dichloromethane for the purposes of EPD of colloidal quantum dots (CQDs) over already reported nonpolar solvents such as hexane and toluene and demonstrate the photosensitisation of nanoparticulate TiO2 electrodes with a range of core and core shell CQDs by EPD
To further analyse the behaviour of CdSe EPD in the optimal solvent, DCM, a more detailed study was carried out measuring absorption spectra at the positive and negative using TiO2 electrodes for each, with the results shown in Figure 2 using a 3.3 nm CdSe CQD sample
Summary
Electrophoretic deposition (EPD) is a relatively new technique finding application in the field of nanotechnology, despite it having been utilised for a number of years in important areas such as the ceramic industry [1,2]. Of special significance, is the application of EPD in regards to colloidal nanoparticle based devices, with diverse examples including Au based photoanodes [3], as well as fluorescent Cu and Au nanosheet based light emitting diodes (LEDs) [4] being demonstrated as of late. The field of colloidal quantum dots (CQDs) has shown a range of noteworthy. It has been shown that photoanodes of quantum dot sensitised solar cells (QDSSC) [8]. Can be efficiently produced using various sizes of colloidal quantum dots (CQDs) and the EPD technique, enabling a significant improvement of photovoltaic characteristics [9]. The EPD approach utilises an electrical field to drive the deposition of CQDs in a solution upon the surfaces of the TiO2 electrodes of opposite polarity. The force driving CQDs deposition in an electrical field is due to the presence of a dipole and/or surface charge in CQDs, whose origin is due to several interactions
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