Photoacoustic and Photoelectrochemical Characterization of CdSe Quantum Dots Grafted onto Fluorine-Doped Tin Oxide (FTO) Substrate

Abstract

We report on the optical absorption properties, measured by the photoacoustic (PA) method, and photoelectrochemical current (PEC) characteristics (including transient measurements) of CdSe quantum dots (Q-dots) grafted onto a planar fluorine-doped SnO2 (FTO) substrate. CdSe Q-dots were fabricated by the chemical solution deposition (CD) technique. With increasing deposition time, the redshift of the PA spectra can be clearly observed and optical absorption in the visible region due to CdSe Q-dots can be demonstrated. The average diameters of the CdSe Q-dots for each deposition time can be estimated using an effective mass approximation producing diameters of 5.1 nm to 5.6 nm for deposition times of 5 h to 25 h, respectively. Thus, PA spectroscopy is useful in obtaining the Q-dots sizes even though there is no use of a high-resolution scanning electron microscope (SEM). An increase in PEC and the clear shift of the spectra to the lower energy region are observed with increasing deposition time, indicating the photosensitization of the FTO electrodes in the visible region resulting from CdSe Q-dots. It can be seen that the maximum value of incident photon to current conversion efficiency (IPCE) is ∼10%, which is higher than that previously reported (∼6%). Transient PEC measurements show that electron recombination in a smaller amount of CdSe Q-dots is lower than that in a higher amount of Q-dots.

Correlation between crystal growth and photosensitization of nanostructured TiO2 electrodes using supporting Ti substrates by self-assembled CdSe quantum dots

“…CdSe QDs were prepared by chemical solution deposition technique [10][11][12][13][14][15][16]31]. Firstly, 80 mM sodium selenosulfate (Na 2 SeSO 3 ) solution was prepared by dissolving elemental Se powder in 200 mM Na 2 SO 3 solution.…”

“…In organic dyes, Ru-based dyes adsorbed on nanostructured TiO 2 with large surface areas absorb solar light energy more efficiently [3]. To achieve light-harvesting efficiency more effectively as well as long-term photostability, semiconductor quantum dots (QDs) have been the subject of considerable interest as a candidate of light harvesters which is an alternative to organic dyes [4][5][6][7][8][9][10][11][12][13][14][15][16][17]. The use of semiconductor QDs as photosensitizers has some advantages in semiconductor-sensitized solar cells [18].…”

“…In this study, nanostructured TiO 2 electrodes using supporting Ti substrates were prepared in order to achieve a direct, high quality Ohmic contact with the electrically conductive substrate and high temperature sinterability. Those electrodes are then adsorbed with CdSe QDs for photosensitizers [10][11][12][13][14][15][16][17]. As the band-gap of bulk CdSe is 1.73 eV [11] and the treatments for QDs formation and adsorption is relatively simple, we choose CdSe as semiconductor QDs for photosensitizer.…”

“…Changes of sample temperature by photothermal phenomenon (proportional to optical absorption) generate pressure changes in the enclosed gas that are converted to electrical signal by the microphone. The application of PA spectroscopy for the characterization of the electronic, optical, defect structures and thermal properties of semiconductors is important and has been demonstrated [9][10][11][12][13][14][15][23][24][25][26][27][28][29][30]. IPCE spectroscopy is a photoelectrochemical technique and it can evaluate the total quantum yield for (1) the electron injection from the CdSe QDs to the conduction band of TiO 2 , (2) the collection efficiency of the injected electrons at the back contact and (3) the hole transfer efficiency to the electrolyte.…”

Interfacial Electron Transfer Reactions in CdS Quantum Dot Sensitized TiO2 Nanocrystalline Electrodes

“…Sensitization of wide band-gap semiconductors, for example TiO 2 , ZnO and SnO 2 , by the QDs is one of the most advantageous structures for solar-energy conversion devices [11,17,21,23,24,30,31]. Figure 9.3 shows a photograph of a CdS QD-sensitized TiO 2 nanocrystalline film (size: 5 Â 5 mm 2 ).…”