Photoelectrochromic cell with a CdS quantum dots/graphitic-nanoparticles sensitized anode and a molybdenum oxide cathode

Abstract

Low cost photoelectrochromic (PEC) cells with a cadmium sulfide (CdS) quantum dots/graphitic-nanoparticles (g-NPs) sensitized titanium oxide (TiO2) film as the photoanode, an electrodeposited molybdenum oxide (MoO3) film as the electrochromic counter electrode and an aqueous electrolyte were assembled for the first time. The oversimplified but surprisingly less used approach of incorporating g-NPs (10–50nm in dimensions) in the photovoltaic film increases the light harvesting ability of the TiO2/CdS film, by the virtue of their high electrical conductivity and a suitably poised work function at 4eV, which maximized electron transfer and transport to the current collector. The proportion of the g-NPs in the film was optimized on the basis of solar cell performances, and the PEC cell with the following configuration: TiO2/g-NPs (90s)/CdS–S2−–MoO3 delivered a power conversion efficiency (PCE) of 4.59% and a short circuit current density of ~17mAcm−2, which were 1.35 times higher than the values obtained for a similar cell with a TiO2/CdS photoanode. Under 1sun illumination and short-circuit conditions, the electrons from the photoanode reach MoO3 via external circuit and it colors deep blue. The transmittance of the device underwent a change from ~58% to ~27% at 630nm and bleached under dark. The transmission modulation varied between 24% and 31% over a wide wavelength range of 500–840nm. The optical change was reversible, demonstrating that energy conversion and saving can be combined efficiently using an inexpensive cell, and thus it has the potential to function as a highly affordable self-powered window.