Study On Enhanced Photovoltaic Performance Of Dye-sensitized Solar Cells Via TiO₂ Surface Modification By Zeolitic Imidazolate Frameworks

Dye-sensitized solar cells（DSCs）,as a new type of solar cells,are different from traditional silicon solar cells.They have high economic efficiency and low process requirements.They have wide application prospects in clean energy field.The charge recombination and the dark current of DSCs will seriously affect the photoelectric properties of the battery,especially photoelectric conversion efficiency.Zeolitic Imidazolate Frameworks（ZIFs）is a kind of zeolite topology polymer porous material with a novel infinite network structure.Research of ZIFs materials used in dye-sensitive cells is still relatively few.In this paper,a very thin blocking layer of a metal organic framework ZIF-8/14 has been successfully coated on the surface of mesoporous TiO₂ films.This paper explored how it affected battery photoelectronic performance and found a new method to improve the photoelectric performance of the dye-sensitive cells.In this paper,ZIF-8 and ZIF-14 films were respectively prepared on the porous TiO₂ photocathode by in situ growth method,and the influence of reaction time,temperature and concentration on the photovoltaic properties of the cells was investigated.The phase and microstructure of ZIFs were studied by XRD,SEM and TEM.The JV and IPCE properties of the cells were measured by electrochemical workstation.The electrochemical impedance spectroscopy was used to analyze the reasons of ZIFs modified TiO₂ photocathode and improved the performance of batteries.In addition,the microstructure of TiO₂ is also designed to be suitable for solid-state dye cells.It was found that ZIF-8 coating layer was prepared on the TiO₂ porous film by in-situ growth using zinc acetate and 2-methylimidazole as precursors and methanol as solvent.With the increase of the temperature,V_OC increaseed slightly and the J_SCC andηincreased first and then decreased;with the the increase of concentration of ZIF-8,V_OC increased firstly and then remained unchanged,J_SC andηshowed the best at 0.25 mM and then decreased.Compared to the uncoated samples,dye-sensitized solar cells with such films exhibit enhanced open circuit voltage(V_OC)and short circuit current(J_SC)by 3%and 21%,respectively,leading to a 9.42%energy conversion efficiency.Analogy ZIF-8,using zinc acetate and 2-ethyl imidazole as precursors,N,N-dimethylformamide（DMF）as solvent prepared a thickness of1-3nm ZIF-14 coating.After ZIF-14 modified battery,V_OC increased by 8%,J_SCC increased by 7%,ηincreased from 6.82%to 7.84%by 15%.The TiO₂ modified with ZIFs materials increased the dye adsorption capacity and reduced the charge recombination,which provides new possibilities for the improvement of the photoelectric performance of the dye-sensitive cells.Spherical TiO₂ nanorod aggregates with a sub-micron level（400-800 nm）with a short rod diameter of about 20 nm and a length of several tens of nanometers were prepared by solvothermal method.The specific surface area was about 100.9 m²/g and the internal pore size was about 16.6 nm,pore volume of about 0.49 cm³/g.Compared with traditional commercial CCIC TiO₂,anodes based TNA retain large pore holes.With the increase of film thickness of TNA anodes,the photoelectric performance of the cell is obviously increased.The TNA anode were used to enhance the J_SC andηby 25.8%and by 23.3%,respectively,compared with the traditional CCIC TiO₂ solar cells with cobalt-gel electrolyte.After 700 h of light stability test,the solar cell stability was good and the photoelectric conversion efficiency increased from 7.1%to 8.0%.This is related to the high specific surface area and porous structure of TNA,which can adsorb more dye molecules.The submicron TNA spherical particles gather around to form large-sized voids,which providing sufficient space for rapid propagation of large molecular size cobalt（II/III）redox in the gel system.