ABSTRACT
Cd is categorized as a toxic material with restricted use in electronics as there are inherent problems of treating waste and convincing consumers that it is properly sealed inside without any threat of precarious leaks. Apart from toxicity, band-gap of CdS is about 2.40-2.50 eV, which results significant photon loss in short-wavelength range which restricts the overall performance of solar cells. Thin film of Zn(O,S) is a favorable contender to substitute CdS thin film as buffer layer for CuInGaSe2 (CIGS), CuInGa(S,Se)2 (CIGSSe), Cu2ZnSn(S,Se)4 (CZTSSe) Cu2ZnSnSe4 (CZTSe), Cu2ZnSnS4 (CZTS) thin film absorber material based photovoltaic due to it made from earth abundant, low cost, non-toxic materials and its ability to improve the efficiency of chalcogenide and kesterite based photovoltaic due to wider band-gap which results in reduction of absorption loss compared to CdS. In this review, apart from mentioning various deposition technique for Zn(O,S) thin films, changes in various properties i.e., optical, morphological, and opto-electrical properties of Zn(O,S) thin film deposited using various methods utilized for fabricating solar cell based on CIGS, CIGSSe, CZTS, CZTSe and CZTSSe thin films, the material has been evaluated for all the properties of buffer layer (high transparency for incident light, good conduction band lineup with absorber material, low interface recombination, high resistivity and good device stability).
ABSTRACT
Free standing, thin films of reduced graphene oxide (rGO) with ZnO, CuO and SnO(2) nanostructures are prepared at a water/toluene interface utilizing simple interfacial reaction and self-assembly. rGO-ZnO, rGO-CuO and rGO-SnO(2) films exhibit unique morphologies such as hexagonal cylinders, elongated splinters, and balls, respectively, wrapped by rGO layers. The hybrid films exhibit surface enhanced Raman scattering (SERS) of rhodamine 6G dye with enhancement factors one order higher than bare metal oxide caused by a synergic effect of charge transfer between the dye, metal oxide and rGO. Doping with Ag+ ions improves SERS enhancement in rGO-AgZnO hybrid films, exploiting the electromagnetic effect of metal surface plasmons. Detection sensitivity up to 10 µM dye with an enhancement factor of 104 is shown. The enhanced photodegradation rate by the hybrid films is utilized for UV induced regeneration of the used SERS substrate and is demonstrated for successive use of different analytes.
ABSTRACT
Binary and ternary hybrid systems of ZnO possessing nanoparticle and nanorod morphologies on reduced graphene oxide (rGO) and rGO with Au nanoparticles are explored as photocatalysts and a comparative study of their photodegradation performance is presented. Various preparation methods such as solution phase and hydrothermal routes have been employed to produce rGO-ZnO hybrids and rGO-Au-ZnO hybrids to impart different morphologies and defect states in ZnO. All the hybrids exhibit faster photodegradation kinetics and the rGO-Au-ZnO system exhibits the highest rate, five times faster than bare ZnO, followed by the binary systems, rGO-ZnO nanoparticles and nanorods. Various factors such as structure, morphology, charge transfer and adsorption are considered to explain the observed kinetics. Excited state electron transfer from ZnO to both rGO and Au levels facilitates faster dye degradation for rGO-Au-ZnO and is reflected as highly quenched band edge and defect state photoluminescence. Intimate physical interfaces formed between rGO, Au and ZnO in the hybrid material during in situ reactions favour charge transfer across the components. The charge transfer contribution even dominates the adsorption factor and the rGO-Au-ZnO system with a slightly lower adsorption capacity than the rGO-ZnO system exhibits a higher degradation rate. A power law dependence of the photodegradation rate on light intensity is also expressed.
