Element Doping Of Halide Perovskite And The Effect On The Solar Cells Performance

Halide perovskite materials have drawn great attention due to the prominent photoelectrical properties.In recent years,the efficiency of organic-inorganic hybrid perovskite solar cells has up to 23%.However,the stability and toxicity of lead-based perovskites hinder its future commercialized development.Therefore,it is essential to solve the stability and toxicity of perovskites.In the paper,we attempt to incorporate potassium iodide(KI)into perovskite precursor solution,changing the morphology of film and improving the crystallinity to prepare the stability and highly efficiency devices.By means of scanning electron microscopy(SEM),grazing incident angle X-ray diffraction(GIXRD),θ-2θ X-ray diffraction(XRD),ultraviolet-visible absorption(UV-vis)and photoluminescence(PL)characterizations,the research indicates that the incorporation of KI can form the two-dimensional(2D)K2PbI4 at the grain boundaries of three-dimensional(3D)perovskite structure.The formation of K2PbI4 passivates the grain boundaries and reduces the defect states.When adding KI into 2D layer perovskite solution,it improves the crystallinity and changes the orientation,therefore,the stability and efficiency of 2D layer perovskite solar cells have both improved.In addition,in order to reduce the toxicity of Pb element,replacing Pb with bismuth(Bi),adopting different cations and optimizing the annealing temperature to improve the performance of perovskite solar cells.The main research results can be included in the following parts:1)Surface passivation mechanism of K+doping in FAMA mixed halide perovskite has been unveiled by the experimental characterizations and density functional theory(DFT)calculations.A potassium-rich phase at grain boundaries of K+doped 3D perovskite thin film is discovered according to θ-2θ XRD and GIXRD characterization.Combined with the theoretical simulation results,the potassium-rich phase can be likely 2D K2PbI4.In addition,the dielectric confinement effect between potassium-rich phase and 3D perovskite crystal results in the red-shift of optical properties.The potassium-rich phase at grain boundaries of 3D perovskite exhibits excellent surface passivation effect and dramatically reduces the defect states,leading to highly stability and efficiency perovskite solar cell.Our works represent an important advance to interpret the local chemistry and the structural stability of perovskite thin films to improve their optoelectronic device performance.2)Upon incorporating KI into 2D layer perovskite solution,combining with GIXRD technology,we investigate the incorporation of KI on the effect of 2D layer structure orientation.Meanwhile,compared with DMSO solvent,hot-casting method and the incorporation of KI method,we find the addition of KI can reduce the formation of n<4 phase,the large grain size,perfect crystallinity and vertical orientation provide favorable conditions for preparing highly stability and efficiency and 2D layer structure perovskite solar cells.The research provides the new approach for adjusting the orientation of 2D layer structure and improves the performance of perovskite solar cells.3)Replacing the Pb2+with Bi3+to reduce the toxicity of Pb,by means of SEM,UV-vis,J-V curve,investigate the different ratio between Csl and BiI3 on the effect of device performance.Meanwhile,when using the different cations,the performance of perovskite solar cells will change.When Rb+as the alterative cation,the performance of device is higher than Cs+ or MA+ due to the small exciting binding energy and better film morphology.Further optimizing the annealing temperature,the PCE can up to 0.31%.Although the efficiency is far below the Pb-based solar cells,we provide the method for preparing the environmental friendly perovskite solar cells and the experimental guidance for future research.