Photoacoustic and Photoelectrochemical Characterization of Inverse Opal TiO₂ Sensitized with CdSe Quantum Dots

Inverse opal TiO₂ may offer a novel and promising solution for enhancing the light harvesting efficiency of dye-sensitized solar cells (DSSCs). Its large interconnected pores enable a better penetration of the dye sensitizers via the matrix pores, making this material surpasses the efficiency of conventional TiO₂ electrodes. Moreover, it also exhibits a photonic band gap that may enable a significant change in its dye absorbance by the adjustment of the photon localization near the red edge of the photonic band gap to the position of dye absorption. In this study, we report a simple method of fabrication of inverse opal TiO₂, wherein the voids in artificial opal latex are filled with nanosized TiO₂ particles by adding a drop of TiCl₄ into the latex matrix, hydrolyzing, and heating. In this process, we investigate the effect of different heat treatment times on the properties of inverse opal TiO₂. Photoacoustic (PA) characterization shows that longer heat treatment times could produce more defect sites. The presence of defects causes the inhibition of electron transfer and results in a decrease in incident photon-to-current conversion efficiency (IPCE). CdSe quantum dots were adsorbed onto inverse opal TiO₂ by chemical deposition. The blue shift of PA spectra relative to the bulk CdSe and the gain in IPCE were clearly observed. This result indicates the quantum confinement effect and photosensitization of CdSe quantum dots.