Electrospray Preparation Of Copper Zinc Tin Sulfide Films And Their Applications As Counter Electrode For Dye-Sensitized Solar Cells

Counter electrode(CE)is a crucial component in Dye-sensitized solar cell(DSSC),working as electron collector from the external circuit and as catalyst for regeneration of redox couple,which is one of the keys to the preparation of high-performance DSSC.However,the most commonly used CE material in DSSC is Pt based material,which is problematic for largescale application in DSSC due to the high cost and lack of abundance in nature.Therefore,the research and development of new CE materials and their thin-film preparation processes have received long-going attention.As one of the important p-type semiconductors,Cu₂ZnSnS₄(CZTS)has the potential to replace Pt as the CE of DSSC devices due to the earth-abundant composition,low-toxicity,high electrocatalytic activity,diverse crystal structures,and excellent optical properties,etc.This work proposes an environment-friendly,solution/suspension-based electrospray(ES)method to prepare CZTS films with different crystal structures,and applies them in DSSC devices.In detail,there are mainly three parts in the work:Firstly,preparation CZTS nanoparticles with different crystal structures:Octadecene and ethylene glycol solvent systems were used,respectively,to prepare kesterite(KT)and wurtzite(WZ)phase CZTS nanocrystalline materials with high purity and small-size.The phase structure,size morphology and optical properties of CZTS nanocrystals were characterized.Secondly,preparation of CZTS film:First of all,employing ethanol as solvent,CZTS liquid dispersion with high dispersion stability was successfully achieved,making it possible to prepare CZTS film by ES method;then,based on the ES method,CZTS film was prepared.The results showed that the film prepared by the ES method has a continuous surface morphology and is firmly bonded to the substrate,signifying a good film quality;lastly,by changing the preparation condition,the best ES-spraying time was proved to be 10 min,which the CZTS film with the best catalyst property was obtained,which is more suitable for DSSC devices.Finally,study of KT/WZ-CZTS-based DSSC devices:The above-mentioned WZ-phase and KT-phase CZTS films were applied to DSSC devices,and the device performance was studied.Under standard light source irradiation,the WZ-CZTS DSSC achieved the photoelectric conversion efficiency of 6.30%,showing 18.4%improvement compared to that from the KT-CZTS DSSC device.This may be attributed to the fact that,unlike the stable KT phase,the metastable WZ phase has a unique hexagonal structure with a disordered arrangement of cations,and thus has a higher carrier density,which can provide better catalytic performance and conductivity.The above results demonstrate that the CZTS film preparation method proposed in this work is a good preparation method for CZTS using as CE in DSSC device.Additionally,Compared to KT-phase CZTS,the WZ-phase CZTS is better when applied in DSSC as CE.