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.