KEYWORDS: Solar cells, Solar energy, Upconversion, Near infrared, Ytterbium, Luminescence, Erbium, Scanning electron microscopy, Absorption, External quantum efficiency
The optical properties of Yb3+/Er3+ doped Y2O3 upconversion phosphor and the enhancement of efficiency of a-Si:H solar cell on incorporation of upconverter are investigated. The Y2O3 host material has high corrosion resistance, thermal stability, chemical stability, low toxicity and relatively low phonon energy (≈ 500 cm-1). Y2O3:Yb3+ (x %): Er3+ (y %) upconversion nanophosphors with different dopant concentrations were synthesized via simple hydrothermal method followed by a heat treatment at 1200°C for 12 hrs. Highly crystalline, quasi-spherical, body centered cubic Y2O3 structure was obtained. The structure, phase and morphology of the nanocrystals were determined using x-ray diffraction and SEM. Following pumping at 980 nm two dominant emission bands were observed at about 550 nm(green) and 660 nm(red), corresponding to 2H11/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions respectively. The dependence of emission intensity on pump power shows that the mechanism involved is two photon absorption. The upconversion phosphor along with a binder is coupled behind the a-Si:H solar cell which absorbs transmitted sub-band-gap photons and emits back the upconverted visible light which can be absorbed by the solar cell. Under suitable intensity of illumination the solar cell short circuit current is found to be increased on adding the upconversion layer.
ZnO has great potential in a wide range of applications such as microelectronics, optoelectronics, and sensors.
Hydrothermal method has proven to be an effective method for the growth of nanostructured materials. Vertically
aligned ZnO nanorods were grown on various substrates such as glass and Si by low temperature hydrothermal method
using ZnO as the seed layer. The thin seed layer on various substrates was deposited by RF magnetron sputtering. The
morphology of the ZnO nanorods can be tuned by varying the sputtering conditions and hydrothermal parameters.
Scanning electron microscopy images confirm the formation of vertically aligned nanorods and XRD pattern shows the
formation of wurtzite structure of ZnO. The sharp (0002) peak in the XRD spectra indicates that the synthesized
nanorods are single crystalline, grown along the [0001] direction. These ZnO nanostructures can be considered as a
potential candidate for sensor and nanowire transistor applications.
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