We present for the first time the synthesis of Eu(3+)-doped β-phase sodium gadolinium fluoride (NaGdF4:Eu) nanocrystals (NCs) using a hydrothermal method and the application of down conversion (DC) NaGdF4:Eu NCs to efficient dye-sensitized solar cells (DSSCs). The as-prepared NaGdF4:Eu(3+) NCs were characterized by X-ray diffraction, photoluminescence spectrometry, and scanning and transmission electron microscopy. DC layers consisting of poly(methyl methacrylate) (PMMA) doped with luminescent NaGdF4:Eu(3+) were prepared and attached onto the back of a prefabricated TiO2 anode to form a more efficient DSSC, compared with a device based on a pure TiO2 electrode. The influences of both doped and undoped NaGdF4 NC layers on the photovoltaic devices were compared and evaluated by the measurement of the device's incident-photon-to-current efficiency (IPCE). An obvious increase in IPCE was observed when the DC layer was added in the device. As the down-converted photons can be reabsorbed within DSSCs to generate photocurrent, the DSSC with a 100 nm thick NaGdF4:Eu(3+) DC-PMMA layer improved photoelectric conversion efficiency by 4.5% relative to the uncoated solar cell. The experiments conclude that NaGdF4:Eu(3+) nanocrystals mainly act as luminescent DC centers and light scatterers in the ultraviolet and visible domains, respectively, for enhancing the spectral response of the device in the measured spectral regime.
Keywords: NaGdF4; down-converting material; dye-sensitized solar cell; lanthanide-doped; nanocrystal.