Study On Preparation Of ZnO-based Nanocomposite Photoanode And Its Application In DSSCs

As the third generation of photovoltaic solar cells,dye-sensitized solar cells?DSSC?have been considered as the most promising photovoltaic solar cells due to their simple manufacturing process?low fabrication cost and stable performance.Generally,the DSSC was composed of a nanocrystalline semiconductor electrodes-sensitized with light absorbing dye as a photoanode,I-/I3-redox couples as electrolytes and platinized conducting glass as counter electrode.The photoanode plays a crucial role in DSSC because they serve as substrates for dye adorption and conductors of photo-generated electrons from dyes to FTO.ZnO has been considered to be the most promising photoanode material to replace TiO₂ due to its high electron mobility,broad-band gap,controllable morphology,and facile preparation.Currently,the efficiency of ZnO based DSSC is generally low,so it is necessary to systematic research for improving the performance of Zn O based DSSC,and lay the foundation for the future application in the field of photovoltaic devices.In recent years,optimizing the structure and function of the photoanode by a compound approach has been an effective way to improve the performance of DSSC.This article will composite the functional materials with ZnO nanoparticles?NPs?to prepare the composites photoanode for improving the performance of ZnO based DSSC by optimizing the electronic transport properties,optical absorption efficiency of the ZnO NPs photoanode and realizing the multi energy conversion of DSSC.The main contents are list as follows:Three kinds of composite photoanodes were fabricated by a doctor-blade technique in this work.They were ZnO nanoparticles/graphene composite photocathode,ZnO nanoparticles/Ag nanowire@ZnO nanorod composite photoanode and ZnO nanoparticles/Bi₂Te₃ nanosheet composite photoanode,and applied to DSSC.The structure,morphology and light absorption of these composite anode films were characterized by XRD,SEM,TEM,Raman,PL and UV.The influence of composite material contents on the on the power conversion efficiency?PCE?and electrical transport properties of DSSCs was investigated systematically by photocurrent density-voltage?J-V?and electrochemical impedance spectroscopy?EIS?.The main results obtained are as follows:?1?The graphene with diffrent contents?0.0-2.0 wt.%?was employed to prepare composite photoanode for DSSCs.The J-V test results show the addition of graphene can effectively improve the efficiency of DSSC.The highest PCE of 3.50% can be achieved in a DSSC with 1.0 wt.% graphene,which is increased by 31% compared with that of the pristine one.The EIS results show that the graphene in the anode can effectively improve the electron collection efficiency and the transfer rate,as well as improve the electron transport property?2?High aspect ratio of Ag nanowires with diameter of 100 nm and length of several microns were fabricated by a simple hydrothermal method.On this basis,a Ag nanowire @ZnO nanorod?AgNW@ZnONR?core-shell structure was synthesized by a two-step solution phase reaction.The ZnO nanorod shells were about 100-200 nm in length and about 20 nm in diameter.?3?The ZnO nanoparticles photoanode modified by AgNW@Zn ONR core-shell structure with different mass ratios?0-2.5 wt.%?were prepared and applied in DSSCs.The UV-vis absorption spectra results and simulation analysis show that plasmonic effecs?Surface Plasmon Resonance,Surface Plasmon Polarization?of Ag nanowires can effectively improve the light absorption and propagation distance of light in photoanode,and greatly improves the light utilization efficiency of the dye in the photoanode.?4?The DSSCs with different AgNW@ZnONR content were prepared and the influence of different AgNW@ZnONR contents on the device performances of DSSCs was systematically investigated.The J-V characteristics reveal that the short circuit current and power conversion efficiency of the DSSC modified by AgNW@ZnONR was highly imporved.Specially,the DSSC with 1.5 wt.% AgNW@ZnONR achieves the maximum PCE of 4.26%,which is increased by 50.5% compared with that of the pristine ZnO NP DSSC.EIS indicates that the AgNW@ZnONR also plays a beneficial role as the electron transport channel,which can accelerate the electrons transport and restrain the charge recombination.?5?The hexagonal Bi₂Te₃ nanosheets?NS?with a side length of 300-400 nm and a distance of 500-600 nm between the opposite edges were successfully synthesized by hydrothermal method.Embeding different Bi₂Te₃ concentrations?0-0.25 at.%?in ZnO NP photoanodes to form Zn O NPs/Bi₂Te₃ NS composite photoanodes and applied to DSSC.When the content of Bi₂Te₃ is 0.15 at.%,the maximum conversion efficiency of the corresponding DSSC is 4.10%,which is 46.95% higher than that of pure ZnO.The thermoelectric effect of DSSCs shows that the addition of Bi₂Te₃ can realize the simultaneous conversion of photoelectricity and thermoelectricity,which can effectively reduce the temperature of the DSSC,improve the electron concentration and the cells stability.The EIS results further demonstrate that Bi₂Te₃ NSs provide direct access to electron transport,extend electron lifetime,suppress charge recombination,and improve electron transport property.