The Study Of Perovskite-type Oxides La_0.67Sr_0.33MnO₃ And La_0.5Sr_0.5CoO₃ As Counter Electrodes In Dye-sensitized Solar Cells

Dye-sensitized solar cell (DSSC) is a light-to-energy conversion device which has attracted great attentions largely because of their low-cost, high-efficiency, simple preparation method, and environment-friendly. Traditionally, DSSC is composed of a dye-sensitized photoanode, a counter electrode and an electrolyte. As one of the most critical components of DSSC, the main function of CE was collected electrons from external circuit and catalyzed the reduction of I3- to I" in the electrolyte. Therefore, this requires that the ideal counter electrode materials must possess high electrical conductivity and excellent catalytic activity. Pt is an ideal CE material which possesses high catalytic activity and electrical conductivity. However, as one of the expensive and scarce resources Pt is not suitable for the large-scale application in DSSC. To overcome this problem, it is necessary to exploit the platinum alternative with high efficiency, low cost, and stable characteristics. So far, several low-cost materials have been developed as the platinum alternative materials, such as carbon material, conductive polymers, transition-metal compounds and composites. However, those CE materials also have their limitations. For example, sulfides are poisonous, noble metals are scarce and the fabrication methods of conductive polymers are complex. Therefore, in this work we try to find a CE material with low-cost, high efficiency, good stability, no toxicity and simple fabrication.The chemical elements of perovskite-type oxides widely exist in the periodic table. In recent years, perovskite-type oxides have attracted great attention and have been extensively research due to their interesting physical properties, such as ferroelectric properties, electrical conductivity, magnetic properties and catalytic performance, etc. As one of important member in perovskite family, La0.67Sr0.33MnO3 (LSMO) and Lao.5Sro.5Co03 (LSCO) have attracted a lot of interest and have been extensively applied in fuel cell due to their excellent catalytic properties, adsorption properties, electrical properties, simple manufacturing method, no toxicity and good stability in thermal and chemical atmospheres. Therefore, we try to synthesis the pure LSMO and LSCO via sol-gel method, and then used as CEs for DSSCs. This work should open up a new ideal for finding potential counter electrode materials in perovskite-type oxides. The main contents are as following:(1) La0.67Sr0.33MnO3 (LSMO) perovskite-type oxide with perfect crystallinity was successfully synthesized by sol-gel method. And then XRD and SEM were used for the analysis of purity and observation of morphology for LSMO sample, respectively. The experiment results show that LSMO particles have irregular shape and average sizes of 50-150 nm without any impurities. Then LSMO sample was used as CE material for DSSC. The photocurrent density-photovoltage (J-V) curves and spectroscopy (EIS) test of the DSSCs with LSMO CEs were measured by using a solar light simulator and the electrochemical workstation, respectively. The result shows that the DSSC with LSMO CE possess a high energy conversion efficiency of 6.62%, and that is 92.6% of the level of Pt CE (7.15%). From the result analysis of EIS test we can know that LSMO possess an excellent stability, good conductive properties and catalytic properties. Experiments show that LSMO was an ideal Pt substitute material with excellent conductive properties and catalytic activity in this work.(2) The pure phase La0.5Sr0.5CoO3 (LSCO) perovskite was successfully prepared by sol-gel method. This method is more suitable for large scale preparation due to its simple preparation technology. From the analysis of XRD and SEM we can know that the as-prepared LSCO shows irregular grains with an average size of 100-400 nm. The photovoltaic tests show that LSCO electrode and Pt electrode obtain an energy conversion efficiency of 7.17% and 7.06%, respectively. The EIS test result show that LSCO possess excellent catalytic activity and high electrical conductivity. Experiments show that LSCO was an ideal Pt electrode substitute material in this work. And it will be a promising research direction to improve the catalytic activity and electrical conductivity of LSCO perovskite.The above results showed that, LSMO and LSCO were ideal CE catalytic materials in DSSCs and both of them show excellent catalytic activity and high electrical conductivity. This work should open up a new ideal for finding potential counter electrode materials for DSSC. In addition, further research to improve the energy conversion efficiency of DSSC by changing the morphology and particle size of CE materials or doping other new matter is needed.