Investigation Of Novel Nanostructure Materials Preparation And Its Application In Thin Film Solar Cell

This thesis is composed of two parts. One part is copper indium gallium selenium (Cu(In,Ga)Se2, CIGS) and copper zinc tin sulfide selenium (Cu2ZnSn(S,Se)4, CZTSSe) thin film solar cells and the other part is NaYF4:Yb/Er/Gd upconversion nanomaterials application in thin film solar cells.For CIGS thin film solar cells. On one side, the absorber CIGS surface was modified with Zn doping using a magnetron sputtering method. CuInGa:Zn precursor films targeting a CuIn0.7Ga0.3Se2stoichiometry with increasing Zn content from0to0.8at%were prepared onto Mo-coated glass substrates via co-sputtering of Cu-Ga alloy, In and Zn targets. The CuInGa:Zn precursors were then selenized with solid Se pellets. The structures and morphologies of grown Zn doped CIGS films were found to depend on the Zn content. At zinc doping level ranging between0.2-0.6at%, the Zn doping improved the crystallinity and surface morphology of CIGS films. Compared with the performance of the nondoped CIGS cell, the fabricated CIGS solar cell displayed a relative efficiency enhancement of9-22%and the maximum enhancement was obtained at a Zn content of0.4at%. On the other side, the buffers in CIGS solar cells were modified. In based mixture Inx(OH,S)y buffer layers were deposited by chemical bath deposition (CBD) technique as an alternative to the traditional cadmium sulfide buffer layer. We investigated the absorber/buffer interface between the chalcopyrite CIGS absorber and CdS or ZnS buffer with an addition of a thin In based mixture layer. It is shown that the presence of thin Inx(OH,S)y at the CIGS absorber/CdS or ZnS buffer interfaces greatly improve the solar cell performances. The performances of CIGS cells using dual buffer layers composed of Inx(OH,S)y/CdS or Inx(OH,S)y/ZnS increased by22.4%and51.6%, as compared to the single and standard CdS or ZnS buffered cells, respectively.Copper zinc tin sulfide (CZTS) is a promising alternative to semiconductors based on gallium or indium as solar absorber material. CZTS consists of abundant and cheap elements and in addition it displays very beneficial properties like a high optical absorption coefficient and an ideal band gap for photovoltaic applications. Thin films of CZTSSe absorber layer was prepared by a nonvacuum spin coating and a subsequent selenization of precursor solutions of metal salts (Cu(CH3COO)2, Zn(CH3COO)2, SnCl2)and thiourea dissolved in pyridine. The morphological, optical properties, structural properties and element composition of each spin-coated and selenized (sulfrized) films were investigated. In addition, large-scale quaternary CZTSe as well as CZTSe/CZTS core/shell nanowires were prepared by using CuSe nanowire bundles as self-sacrificial templates. CZTSe nanowires were prepared by reacting CuSe nanowire bundles with Zn(CH3COO)2and SnCl2in triethylene glycol. X-ray diffraction (XRD) and selected area electron diffraction studies show that stannite CZTSe is formed. The formed CZTSe nanowire bundles are with diameters of200-400nm and lengths up to hundreds of micrometers. CZTSe/CZTS nanocable bundles with similar morphologies were grown by addition of some elemental sulfur to the reaction system for growth of CZTSe bundles. The stannite CZTSe/kesterite CZTS core/shell structure of the grown nanocables was confirmed by XRD and high-resolution transmission electron microscope investigation. The influence of S/Se molar ratio in the reaction system on the crystallographic structures and optical properties of CZTSe/CZTS nanocables was studied. The obtained CZTSe/CZTS core/shell nanocable bundles show broad and enhanced optical absorption over the visible and near-infrared region, which is promising for the use in photovoltaic applications.Near-infrared (NIR) to visible up-conversion (UC) NaYF4:Yb/Er/Gd nanorods in combination with gold nanostructures were prepared and applied to flexible amorphous silicon solar cells. The attachment of Au nanoparticles onto NaYF4:Yb/Er/Gd nanorods resulted in a more than three-fold increase in UC emissions, while the formation of continuous and compact Au shells around the nanorods suppressed the emissions. The related interaction mechanisms of UC emission of NaYF4:Yb/Er/Gd nanorods with plasmon modes in Au nanostructures are analyzed and discussed. Photocurrent-voltage result demonstrated that UC of NIR light led to a16-fold to72-fold improvement of the short-circuit current under980nm illumination compared with a cell without upconverters. A maximum current of1.16mA and quantum efficiency of0.14%were obtained for the cell using UC nanorods coated with Au nanoparticles under the980nm laser illumination.The UC photoluminescence in a Ag nanoparticles/SiO2/NaYF4:Yb/Er/Gd film sandwich structure were investigated. The influence of SiO2thickness on the UC emission intensity was also studied. Intensity of both green emission around540nm and red emission around660Cnm are increased obviously compared to reference of the UC film without Ag nanoparticles coverage. The thin SiO2film reduced the energy transfer between Ag nanoparticles and NaYF4:Yb, Er, Gd UC film, and surface plasmon resonance enhancement effect is dominant in this structure. Time-resolved photoluminescence spectroscopy reveals that the fluorescence lifetimes were reduced both for green and red emission. Photoluminescence spectroscopy and excitation power studies showed that Ag nanoparticles can also modify the UC process in this sandwich structure.