Growth Of Organometal Halide Perovskite Single Crystal Thin Film And Fabrication Of Photovoltaic Device

Organometal halide perovskite has attracted tremendous attention in photovoltaics since 2009 and it has emerged as promising light absorbers for the third-generation photovoltaics.Due to lower trap state densities and longer carrier diffusion length of organometal halide perovskite single crystal thin films（PSCTFs）compared to polycrystalline counterpart,it’s an ideal candidate for optoelectronic application.However,the growth method for PSCTFs with controllable thickness and large lateral size is limited.In this thesis,we develop space confined sandwiched growth strategy that PSCTFs were grown from a perovskite precursor solution flowing through the micron-thick gap between hydrophobic electron transport layer and hole transport layer.By research we can find:1.The biggest lateral size and the thinnest thickness of CH₃NH₃PbBr₃（MAPbBr₃）and CH₃NH₃PbI₃（MAPbI₃）single crystal thin films that we had grown were 10?10mm²,1.7?m and 5?4 mm²,2.7?m,respectively.By observation under optical microscope,both crystal thin films showed clear profile and square shape.The crystal thickness was largely flat and no grain boundary was found in SEM cross-sectional image.2.By characterization of X-ray diffraction（XRD）,the highly-orientated property of both PSCTFs were found and top surface of MAPbBr₃ single crystal thin film is（100）facet of cubic crystal system.As for MAPbI₃,top surfaces are the nearly-equivalent（200）and（110）facets of the tetragonal crystal system.When conducting rocking curve of the（200）facet diffraction of MAPbBr₃ single crystal thin film,a small full width of half maximum（FWHM）of 0.17°was measured.3.Optical properties of PSCTFs were characterized by absorption spectroscopy as well as steady-state and time-resolved photoluminescence（PL）.The results demonstrated that the absorption edge is located at 546 nm together with PL peaks located at 550 nm for MAPbBr₃ single crystal thin film.In contrast,absorption edge is located at 798 nm together with PL peaks located at 785 nm for MAPbI₃ single crystal thin film.From time-resolved photoluminescence spectrum（TRPL）of PSCTFs,a fast component ofτ=136.1±4.2 and 92.9±0.2 ns together with a slow decay ofτ=876.6±11.4 and 483±4.2 ns were measured for MAPbI₃ and MAPbBr₃ single crystal thin films,respectively.By constructing standard space-charge-limited-current model,trap state density(N_traps)and mobility can be extracted.As for MAPbBr₃ thin film,N_traps=1.7?10¹³ cm^-3,?_e=21.4±0.8 cm² V^-1 s^-1 and?_h=26.7±1.8 cm² V^-1 s^-1.Thus,carrier diffusion length（L）can be calculated as L_e=3.6±0.1μm and L_h=4.1±0.2μm.As for MAPbI₃ thin film,N_traps³?10¹³ cm^-3,?_e=35.1±4.0 cm² V^-1 s^-1,?_h=18.7±1.1 cm² V^-1 s^-1.Accordingly,carrier diffusion length can be calculated as L_e=8.7±0.5μm and L_h=6.2±0.2μm.In addition,perovskite solar cells are conventionally fabricated into normal-or inverted-structure.Hence,we examined the feasibility of another device structure of the perovskite single crystal solar cells,which is called sandwiched structure.The coincidence between the external quantum efficiency curve of the function device with the structure of ITO/poly-PCBCB/MAPbI₃/PTAA/ITO and that of stable absorption spectrum,which were both largely flat between 400-790 nm but drop exponentially at longer wavelengths,reflects effective harvesting photoinduced charge-carriers by the two electrodes.What’s more,it’s consistent with the relative thickness of the sandwiched MAPbI₃ layers than its charge-carrier diffusion length.Owning to the great impermeability of the sandwiched structure,it can endure the extreme condition under boiling water,which highlighted its excellent impermeability from water and heat.