The Research On Preparation And Properties Of ZnO-TiO₂Core-shell Structure And Its Application In Dye Sensitized Solar Cells

Dye sensitized solar cells is a noval third generation solar cells. Its current maxium conversion efficiency has achieved12.3%. The recombinations of photo induced electron restrict the improvement of conversion efficiency. Photoanode plays a key role in DSSC as dye loader and electron transfer and transmission. Recently, research group use unique physics and chemical properties of ZnO and TiO2, developed new route for photoanode design. This paper introduced take advantage of surface defects of ZnO as nucleation centre, and epitaxial growth branched structure TiO2core-shell photoanode. The shell could growth from defects, and good for electron transfer from TiO2to ZnO. Element doping could adjust the energy band of ZnO/TiO2prompt electron transfer and transmission, passivating interface defects. The research content as follow:(1) Prepare ZnO seed layer with sol-gel method and magnetron sputtering, as substrate to overcome lattice mismatch. Compare the microstructure of different methods. Optimize magnetron sputtering parameter, about deposition power, O2/Ar ratio and spacing adjustment of ZnO seed layer. Investigate the properties of Al doping ZnO seed layer with orthogonal experimental design.(2) Prepare ZnO and Al:ZnO nano array on seed layer by chemical bath deposition. Adjust Zinc concentration of solution, temperature, duration and Al doping content. Explore the optimized parameter and nano array growth mechanism. With continuous chemical bath deposition method, optimize the nano array, prompt the nucleation and growth of ZnO nanorod.(3) Branched continuous TiO2shell structure were obtain from magnetron sputtering. Investigate O2/Ar ratio, heat treatment temperature, and microstructure. Discuss the shell formation mechanism.(4) Prepare DSSC module with different photoanode. Study the conversion efficiency, open circuit voltage, short circuit current, and fill factor. Investigate interface transfer and transmission of photo induced electron with electrochemical impediance spectrum. Discuss the mechanism of core-shell structure for inhibition recombination. The results have achieved from experiment and analysis as follow:(1) The ZnO seed layer prepared by sol-gel mothod has strong crystal orientation with increasement of heat treatment temperature. The formation of stipe grain has strong correlation with the decrease of surface energy of nanocrystalline. The optimized parameter of ZnO seed layer prepared by magnetron sputtering is spacing50mm, sputtering power100W, O2/Ar ratio1:3. The internal stress of seed layer reached minimum when temperature is400℃. The optimized parameter of Al:ZnO seed layer is200℃,40W, oxygen flux20%, and treatment temperature is400℃. Under these condition, Al:ZnO layer has best conductivity and photoluminescence.(2) Preferred orientation ZnO nano array with wurtzite structure was affect by substrate and concentration. The increasement of temperature and duration could prompt growth of ZnO nanorod perpendicular substrate. The diameter of nanorod increased with concentration elevated. Continuous chemical bath deposition could maintain concentration in solution, to the benefit of directional growth of nanorod. The conversion efficiency of DSSC modules based c-CBD method reached0.31%. Doping conten2%of Al:ZnO have optimized electrical properties and photoluminescence. When concentration is0.01mol/L, the module of5%Al doping ZnO nanoarray has reached0.42%.(3) ZnO-TiO2core-shell structure prepared by magnetron sputtering with different O2/Ar ratio varied from1:1to1:3. The formation of shell was affected by gas-solid growth pattern, and finally achieved TiO2shell with rutile structure. Core-shell strucre could effectively prompt electron transmission and inhibite recombination. The conversion efficiency reached0.94%. Core-shell structure with different dye load content has132%efficiency compared with ZnO nano array. Chemical impediance spectrum reveals TiO2shell could effectively accelerate electron transter and transmission, inhibite reverse transmission and recombination.