Cu(In, Ga)Se2薄膜太陽能電池與TiNb2O7鋰離子電池陽極材料之製備與特性分析

Abstract

Cu(In, Ga)Se2 thin films and TiNb2O7 powders were prepared for the application of Cu(In, Ga)Se2 solar cells and lithium-ion batteries, respectively. For improving the photovoltaic properties of the solution-based Cu(In, Ga)Se2 films, samarium ions were added into Cu(In, Ga)Se2 films in the first section of this thesis. The incorporation of samarium ions facilitated the formation of the Cu2-xSe phase during the selenization reaction to promote the growth of Cu(In, Ga)Se2 grains, thereby decreasing defect density in the Cu(In, Ga)Se2/cadmium sulfide (CdS) interface and the absorber layers. Compared with pristine Cu(In, Ga)Se2 films, the conversion efficiency of the prepared solar cells increased by 26.6% (from 8.62% to 10.91%) when 0.5 mol% samarium ions were doped into Cu(In, Ga)Se2 films. In the second section, the incorporation of copper-indium back-end layer in the precursor films for preparing Cu(In, Ga)Se2 films was investigated. The incorporation of copper-indium back-end layer enhanced the internal diffusion between gallium-ion and indium-ion during selenization reaction to build up a gradient profile of bandgap distribution in the prepared films. The gradient bandgap reduced the carrier recombination and improve the carrier collection of solar cells. In contrast to the pristine precursor films, the precursor film with a copper-indium back-end layer increased the conversion efficiency of prepared solar cells from 8.34% to 11.13%. In the third section, the modified microemulsion process was utilized to prepare TiNb2O7 nanoparticles. In the microemulsion process, the thermodynamically stable solution containing nano-sized water-in-oil droplets provided an independent environment as nanoreactors to prevent particle growth. The microemulsion-derived TiNb2O7 nanoparticles possessed a large specific surface area for providing a large contact area between the active materials and electrolyte, thereby increasing the diffusivity of lithium ions. The microemulsion-derived TiNb2O7 nanoparticles exhibited satisfactory discharge capacities at 0.1 C. In the fourth section, the preparation of TiNb2O7 powders via a post treatment process was investigated. After the post treatment process, the bandgap values of prepared samples were decreased because the formation of oxygen vacancies increased the impurity level in the forbidden gap of TiNb2O7. The well-controlled amounts of oxygen vacancies in TiNb2O7 powders were effectively reduced the charge transfer resistance of prepared batteries. In comparison to the pristine TiNb2O7 powders, the rate capability at 20 C of the prepared batteries containing the reduced TiNb2O7 powders was improved. In the fifth section, coating was deposited on the surface of TiNb2O7 powders for enhancing the cyclability of prepared batteries. A coating provided additional redox couples for electrochemical reactions to compensate the degraded discharge capacity of TiNb2O7 caused by the coating layers. A coating prohibited direct contact between TiNb2O7 and electrolyte to suppress interface reactions. When TiNb2O7 was coated with a coating, the capacity retention of prepared batteries at 0.2 C for 100 cycles was significantly improved. This thesis demonstrated that the new methods for enhancing the conversion efficiency of Cu(In, Ga)Se2 solar cells and the novel preparation processes for synthesizing TiNb2O7 powders with high electrochemical properties and a long-term cyclability were successfully developed.