Study On Nano TiO₂ Solar Cells Sensitized By Natural Dye

At present, developing new energy and protecting environment were the priority of humanity. One of the most effective methods to settle the two tasks was the valid development and utilization of solar energy. Dye-sensitized solar cells(DSSCs) have the advantages of simple preparation, low costs and no pollution. Dye sensitizer, as an important and indispensable part of the DSSC, plays a decisive role on photoelectric performance of the DSSC. Synthetic dyes have generally more expensive price and relatively complex preparation process. While natural dyes have low cost, simple preparation process, no pollution, etc., and could be used as sensitizer in DSSC directly. In this paper, natural dyes extracted from Henna flower were used as sensitizers. The photovoltaic performance of natural dyes sensitized nano Ti O2 solar cells was studied. The natural dye from henna flowers was extracted with water and ethanol and its composition was analyzed by high performance liquid chromatography-diode array detector, fourier transform infrared spectroscopy and nuclear magnetic resonance. The photovoltaic performance of natural dyes sensitized nano TiO2 solar cells was explored. The main achievements are as follows:(1) The natural dyes from henna flower were extracted with ethanol and then used as sensitizer of DSSC. The dyes extracted with solvent with different pH values were tested by UV-Vis absorption spectroscopy. The photovoltaic performance of DSSC sensitized by the henna flower dyes was analyzed. Under neutral(original pH value) conditions, the sensitizer active ingredients at the visible region area are chlorophyll a, carotenoids, etc. Under alkaline conditions, due to the dissociation phenolic hydroxyl proton from lawsone, luteolin, apigenin and others, UV absorption peak had red shift and the absorption intensity increased. Under acidic conditions, chlorophyll lost magnesium in the porphyrin ring to become pheophytin, so the main absorption peak were all at around 420 nm and 670 nm. At pH = 5, the open circuit voltage, short circuit current density, fill factor of henna flower natural dye-sensitized TiO2 solar cells were 0.39 V, 0.66 mA?cm-2, 0.60, respectively. As a result, the photoelectric conversion efficiency reached 0.15% and IPCE at 400 nm reached 1.7%.(2) The natural dyes from henna flower were extracted with water and then used as the sensitizer of DSSC. The adsorption and desorption performance of the extracted dyes in solutions with different pH values was tested. The results showed that it has good adsorption performance at pH = 4. There were higher absorption peaks at 380 nm and 670 nm in UV-Vis spectra. This indicated that the main active sensitizer ingredient was lawsone. The extracted henna flower natural dyes with different concentrations in water were used to sensitize TiO2 solar cells. The results showed that at a concentration of 7.5g / L, the open circuit voltage, short-circuit current density and fill factor of the DSSC were 0.25 V, 0.22 mA ? cm-2 and 1.06, respectively, the photoelectric conversion efficiency achieved 0.06%, and the IPCE reached 0.8% at about 400 nm.