Assembly of CdS quantum dots onto mesoscopic TiO₂ films for quantum dot-sensitized solar cell applications

Abstract

Colloidal cadmium sulfide (CdS) quantum dots (QDs) were prepared and surface modified by mercaptosuccinic acid (MSA) to render a surface with carboxylic acid groups (MSA-CdS). The MSA-CdS QDs were then assembled onto bare TiO(2) mesoporous films using the carboxylic groups/TiO(2) interaction. The TiO(2) film was also surface modified by 3-mercaptopropyl trimethoxysilane (MPTMS) or 3-aminopropyl-methyl diethoxysilane (APMDS) to prepare, respectively, a thiol (-SH) or amino (-NH(2)) terminated surface for binding with the CdS QDs. The experimental results showed that the MPTMS-modified film has the highest adsorption rate and adsorption amount to the CdS QDs, attributable to the strong thiol/CdS interaction. In contrast, the adsorption rate and incorporated amount of the QDs on the bare TiO(2) film are much lower than for the silane-modified films. The incident photon-to-current conversion efficiency (IPCE) obtained for the CdS-sensitized TiO(2) electrode was about 20% (at 400 nm) for the bare TiO(2), 13% for the MPTMS-TiO(2), and 6% for APMDS-TiO(2). The current-voltage measurement under dark conditions reveals a higher dark current on the MPTMS- and APMDS-modified electrodes, indicating a lower coverage ratio of CdS on these TiO(2) films. This result is attributed to the fast adsorption rate of CdS QDs on the bottleneck of a mesopore which inhibits the transport of the QDs deep into the inner region of a pore. For the bare TiO(2) film, the lower incorporated amount of CdS but higher energy conversion efficiency indicates the formation of a better-covered CdS QDs monolayer. The moderate adsorption rate of MSA-CdS QDs using the carboxylic acid/TiO(2) interaction is responsible for the efficient assembly of QDs onto the mesoporous TiO(2) films.

Highly Efficient Quantum‐Dot‐Sensitized Solar Cell Based on Co‐Sensitization of CdS/CdSe

“…The variation of UV-vis spectra with CBD cycles obtained in this work are similar to that shown in our previous papers. [4,16,18] For comparison of the light absorption properties of QD-sensitized TiO 2 films, the spectra of the electrodes prepared by 3 or 4 CBD cycles are shown in Figure 3. For the CdS-and CdSe-modified electrodes, the absorbance intensities are similar at the excitonic peaks.…”

Quantum‐Dot‐Sensitized Solar Cells

“…There are two limiting factors for colloidal QDSCs: first, the chemical nature of the bifunctional molecular linker plays a significant role in charge separation and subsequently in the light to electric power conversion efficiency of the cell. [96,[104][105][106] Secondly, the surface coverage of QDs on the wide-bandgap nanostructured metal oxide is usually poor when ex situ QD preparation is used. [99] For efficient solar cell operation, strong light absorption followed by efficient charge separation is required, which so far has been more difficult to achieve with QDSCs based on ex situ QD preparation .…”

Light Emitting “Polymer-Nanoparticles” Coatings on Macroporous Silicon Substrates

“…Nanostructures based on semiconductor materials have promising applications including the optoelectronic devices such as light-emitting diodes [3] and next generation of quantum dot solar cells [4]. Moreover, nanoscale semiconductors functionalized with biomolecules are promising as molecular fluorescent probes in biological applications [5].…”

“…This is due to photoluminescence excitation in the visible spectral range after illumination by UV light. This effect is useful to increase the spectral range of light absorption by solar cells [4] because of conversion of UV radiation into visible light. Local electric fields at the "macroporenanocoating" interface [15] increase the resulted electron flow from the silicon matrix toward the nanocrystal layer and reduce the non-radiative recombination in light-emitting nanocoatings.…”