Photoanode Preparation And Dye Stnsitized Solar Cells (DSSCs) Study

Dye sensitized solar cells (DSSCs) attracts wide attentions due to their relative high powerconversion efficiency, low cost, simple preparation process and environmental friendliness. Atypical DSSC device is composed of four parts; they are the Photo anode, dye, electrolyte and thecounter electrode. Among them, the morphology and structure of anode plays a main role. Thecrystal grain size, the pore size and the porosity of the photo anode film affects the short-circuitcurrent directly, that will improve the performance dramatically. Compared with the porousnanocrystal photoanode, zero dimensional spherical structure photo anode film has been consideredto be an effective anode because it can absorb more dye and is more suitable for the penetration ofelectrolyte. Focusing on DSSC, this work mainly includes the following parts:(1) Using P25(Degussa TiO2P25) powder as raw materials, some traditional methods suchdoctor-blade, spin-coating, screen printing and hydrothermal are studied. The influences onthe performance of DSSC for their differences among slurries and processes are analizeddetail. The advantages and shortcomings of these methods are described respectively.(2) As a powerful tools to fabricate thin films, Electrostatic spray (ES) has started to getattention for TiO2electrodes preparation in recent years. Using ethanol as dispersionsolvent, photoanodes are fabricated with different solvent concentration, and optimalcondition was realized with corresponding discussion. The best DSSC performance dataare Jsc=9.60mA/cm2, Voc=0.76V, FF=63%, PCE=4.6%.(3) Employing different dispersion solvents containing different number(s) of hydroxyl groupin one molecule, using ES method, the properties of TiO2suspension and thecorresponding photoanode and device performance are studied. The results show that underthe same ES condition, Employing ethanol possessing one OH group within one molecule,sta-ble TiO2suspension can only exist at low TiO2concentra-tion, e.g.7.5%. On the otherhand, when EG or glycerol was used, who possesses2or3OH groups within one sol-ventmolecule, stable suspension can be obtained with TiO2concentration up to40%. Due to thepossibility ofhigher TiO2concentration in the suspension, employing solvent of EG orglycerol can reduce the lm preparation time signi cantly, which is bene cial for massproduction. Additionally, suspension with higher TiO2concentration and higher viscosity tends to yield larger secondary TiO2spheres leading to considerably higher Jsc because ofbetter light scattering.(4) For mass production using ES, high TiO2density is highly desired. Based on the previouswork of this thesis, both ethylene glycol and glycerol are hopeful. Thus, in this part thesetwo dispersion solvents are examined in detail. We find that due to the over dense, lowconductivity and too high boiling point of glycerol, this solvent is not applicable forpreparation of TiO2photoanode. In contrast, photoelectrodes using40wt.%suspensions ofTiO2nanoparticles in ethylene glycol are promising. It is also found that a suitabletemperature range (150C in this work) is important to ensure complete drying ofsuspension droplets while avoiding creation of hollow particles, because the hollowparticles exhibit signi cantly lower carrier mobility and less power conversion ef ciency.The as-sembled DSSC devices fabricated under150C reached power conversionef ciency up to6.81%.(5) Some counter electrodes are made by ES method.We improve our experimental device forIron ions lead into the lose efficacy of the counter electrodes. The stainless steel nozzle inES device is replaced by a graphite rod. We fabricate some counter electrodes by ESprocess whose performances are better than other methods.Reflect films can improve the power conversion efficiency dramatically for they can reflectlight in the DSSC device that means increasing the utilization of the incident light ray.Base on this theory, we simulate the optical field distribution in the DSSC device with areflect films on surface externally and internally of the counter electrode. The reflect filmsare fabricated on the surface of the counter electrode of DSSC by evaporation. The resultsof these experiments illustrate that the reflect film deposited on internal surface of counterelectrode can inprove short circuit current density remarkably.