Structural Design And Photoelectronic Performance Of P-CuSCN Thin Film

CuSCN is a kind of wide bandgap p-type semiconductors with good conductivity,light transmittance and carrier mobility.It has been paid more attention and grained great research interest in the field of photoelectrochemistry.Presently,various of synthesis approaches for CuSCN thin film have been applied including impregnation method,liquid phase evaporation method,copper anodic electrolysis method and electrochemical deposition method.Among them,the electrochemical deposition method is much more widely used,because of its advantages of well deposition in the substrates for large area usage as well as the easily control of the composition and thickness of the CuSCN thin film.As reported,CuSCN thin films have good photoelectrochemical(PEC)performance which is closely related to the morphology of the film.The structure of the p-CuSCN films always have many defects which causes large interface impedance and relatively short carrier's lifetime,thus decreases the performance.Therefore,in this thesis,electrochemical deposition method was employed to prepare p-CuSCN thin films,and the corresponding structure and photoelectric properties of the films were adjusted by changing the different experimental parameters,and also the intrinsic relationship between the structure and PEC performance of the film was also investigated.Meanwhile,we try to modify the CuSCN thin film in terms of structures to improve the PEC performance,and also further explored the mechanism by using,various characterization methods.The main research contents in this thesis is as follows:1.Preparation and photoelectrochemical performance of p-CuSCN semiconductor nanorod thin filmsThe p-CuSCN nanorod thin films were prepared by electrochemical deposition.The structure and photoelectric properties of the films were regulated by changing electrochemical deposition voltages.The experimental results show that the p-CuSCN nanorod film deposited at-0.4 V possessed more uniform nanorod structure,and has exhibited better PEC performancecomparing,with other thin films deposited at other potentials(i.e.,-0.1 V,-0.2V and-0.3 V).2.Preparation and photoelectrochemical performance of carbon quantum dots-decorated p-CuSCN nanorod thin filmsThe p-type CuSCN nanorod film were modified by in-situ decoration of carbon quantum dots(CQDs)to further improve the photoelectric properties of CuSCN thin films.The CQDs-decorated CuSCN thin films were prepared by one-pot electrochemical deposition method,which was performed in the electrolyte containing a certain amount of CQDs solution.Experimental results show that the CQDs were successfully decorated on the CuSCN nanorods,and the optical properties of the CQDs/CuSCN thin films were significantly improved in the visible light region.The flat band potential of the CQDs/CuSCN thin films decreased from 0.3 eV to 0.2 eV,and the photocurrent intensity enhanced about 6.5 times obviously.The results also showed that the CQDs can effectively improve the photoelectric properties of CuSCN films.The results confirmed that the impedance of CQDs/CuSCN thin films was lower than that of the CuSCN films,and the carrier migration and separation of the CQDs/CuSCN films were better than that of the CuSCN films,the lifetime of the photoinduced carrier was also improved,(increased from 66.4 ms to 108.32 ms),leading to an improvement of the photoelectric performance.3.Preparation and photoelectrochemical performance of p-CuSCN thin films deposited on KSCN-pretreated FTO substrateThe FTO conductive substrate was pretreated by being immersed in KSCN solution,and then the CuSCN nanorod thin films were deposited on the KSCN-pretreated FTO substrate,and the influence of the KSCN pretreatment on the PEC performance of the CuSCN thin film was also explored.Firstly,the FTO glass was immersed into the KSCN solution for a period of time,and then the CuSCN thin films were deposited on the KSCN-pretreated FTO glass.The photoelectric properties of the obtained CuSCN thin films was subsequently examined.The results showed that KSCN pretreatment process can change the morphology and improve the photocurrent of the CuSCN thin film.The photocurrent of the CuSCN film deposited on the KSCN-pretreated FTO was about 13 times than that of the CuSCN thin film,which could bedescribed to the fact that the KSCN pretreatment could significantly improve the mobility and lifetime of photogenerated carriers for the CuSCN thin film.According to the exploration of the influence of KSCN pretreatment on the structure,we concluded that after pretreatment the surface of FTO absorbed KSCN particles via the interaction between the SCN-and conductive oxide,which formed KSCN adsorption layer,thus changed the structure and morphology of the FTO and also improved the surface hydrophilicity of the FTO.The KSCN pretreatment process was beneficial to the electrochemical deposition process of CuSCN thin film on the FTO substrate,and accordingly a well-organized and more uniform CuSCN nanorods film could be formed which greatly improved the PEC properties of the CuSCN thin films.