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.
β-In2S3 films were grown on glass and quartz substrates by the rapid heating of metallic indium films in H2S atmosphere. The effect of sulphurisation temperature and time on the growth of single phase In2S3 and its electrical and optical properties have been investigated. The influences of processing parameters on the electrical and optical properties have
been studied. The band gaps of In2S3 films were in the range 1.9 eV to 2.3eV. All the films exhibit n-type conductivity. The studies on temperature dependence of conductivity indicate a variable range hopping mechanism.
Zinc sulphide thin films were prepared by chemical bath deposition (CBD) and the properties of these films are compared with those deposited by Physical vapour deposition (PVD). The variation in the optical and electrical properties of the CBD grown ZnS films with the pH of the reaction mixture was investigated. The chemically deposited
ZnS films showed a wide band gap of 3.93eV and a transparency of more than 80% in the visible region. The lowest resistivity of ~104 Ωcm was obtained for the films prepared from a chemical bath of pH 10.6. The refractive index, extinction coefficient and the dielectric constants of CBD ZnS films are also reported.