Light localization and photoelectrochemical studies at CdSe and CdTe nanostructured films for enhancing solar energy conversion -

Abstract

Solar energy conversion in quantum dot sensitized solar cells (QDSSCs) could be improved by localizing light in nanostructured ordered systems or photonic crystals (PC) that exhibit a periodic modulation of the refractive index on the order of the wavelength of light. Another way of enhancing the efficiency of solar cells is by slowing light via multiple internal scattering in disordered PCs, called photonic glass (PG), assembled from the same PS spheres at higher ionic strength. In this project, the role of disorder versus order on absorbance and photocurrent enhancement is investigated in CdSe sensitized titania films. The ordered films led to a significant enhancement at the red edge of the stop band whereas the disordered films showed lower enhancements in this region but comparable gains within the stop band of the inverse opals. In a further study, photoconversion was extended to the visible region using the small band gap CdTe QDs although few studies on QDSSCs focused on using CdTe QDs due to its instability. In our lab, nanocrystalline titania films were sensitized with CdTe QDs via the successive ionic layer adsorption and reaction (SILAR) method. The photoelectrochemical behavior of the CdTe-sensitized films was studied in alkaline Se²⁻ electrolyte and compared to S²⁻. The films exhibited significant photocurrent generation and stability in selenide which is attributed to efficient quenching of anodic dissolution by Se²⁻ scavenging the hole. Moreover, the photoelectrochemical behavior of Q-CdTe sensitized ordered titania inverse opals was compared to that of disordered templates. The Q-CdTe sensitized inverse opals showed significant enhancements at the blue of the stop band. Similar enhancements were also obtained in photonic glass due to light localization through multiple scattering in the disordered medium.