Synthesis And Properties Of Copper Zinc Tin Selenide Nanomaterials

In recent years, researchers have investigated various nanoscale materials for low-cost high-efficiencysolar cells. Because of its similar crystal structure and physicochemical properties (band gap:0.8-1.6eV,absorption coefficient:>10⁴cm^-1) to CuInGaSe₂（CIGSe）, and the abundance of its elements,Cu₂ZnSnSe₄（CZTSe） is considered to be one of the most promising alternatives for CIGSe in solar cellmaterials. CZTSe nanomaterials were synthesized via physical method at the beginning, the key issue forphysical approach was the elimination of the by-products of the binary and ternary phases. At present, thewidely adopted wet chemical route for researchers is hot-injection method, however, this way stillpossesses some disadvantages, such as protective atmosphere, tedious complicated synthesis procedures,the use of high cost organic solvent, or low yield. It is necessary to develop a more facile method tofabricate CZTSe for the development of CZTSe solar cells.To date, CZTSe is mostly used as absorber in inorganic compound thin film solar cells, but the studiesof the properities of CZTSe have been still limited. In this work, we investigated the properties of CZTSeused as absorber in solar cells. Furthermore, dye-sensitized solar cells （DSSCs） are under the spotlight dueto the advantages of low cost, environmental friendliness, simple preparation procedures, and so on. One ofthe most important components in the DSSCs is the counter electrode （CE）, which collects electrons fromexternal circuit and catalyzes the reduction of triiodide ions in electrolyte. The conventional Pt CE is scarceand expensive, which limits the potential large-scale applications. Thus, CZTSe proposed to use as analternative CE in DSSCs may pave a promising way to new class of CE materials for DSSCs.In this dissertation, CZTSe was synthesized by facile one-step solvothermal approach to thedrawbacks of the hot-injection method. Different morphologies of CZTSe were obtained by changingreaction conditions. The morphologies and componets were characterized by XRD, SEM, TEM, XPS,Raman spectrum, and so on. It was demonstrated that the morphology and the band gap can be adjusted bychanging the reaction time in the results. As absorber in thin film solar cells, the absorption characteristicsand photoelectric separation characteristics of CZTSe thin films were characterized in this work. As CE inDSSCs, the properties of CE were also measured. The Pt-like electrocatalytic activities of the synthesizedCZTSe film were demonstrated by cyclic voltammetry experiments. The resistivities of CZTSe thin films were tested using four-point probe technique. The photovoltaic properties of the DSSCs were alsoinvestigated by photocurrent-voltage （J-V） measurements, and the photovoltaic parameters of the DSSCswith CZTSe CE were compared with that of the DSSCs with Pt CE. The J-V results demonstrated that thethickness of the film affected the photocurrent density and fill factor remarkably, which was resulted fromthe differences of electrocatalytic sites and resistance with different thickness films. It was concluded thatthe thiner film was beneficial to the higher solar energy conversion efficiency.