Preparation And Study Of Organic-inorganic Hybrid Perovskite Ferroelectric Multifunctional Materials And Tin(Ⅱ)-based Perovskite Solar Cells

Organic-inorganic hybrid perovskite-type materials,which are able to combine desirable characteristics from both organic and inorganic components,have been extensively studied due to their rich physical properties and promising applications.In recent years,the successful application of three dimensional ABX3 metal halide perovskites as light absorbers in solar cells makes organic-inorganic hybrid perovskites more and more attractive.In the organic-inorganic hybrid perovskite structure,the organic cations occupy the cavities formed by inorganic frameworks.The dynamics of the cation may change upon external stimuli like temperature,which can induce ferroelectric phase transitions.Thus,organic-inorganic hybrid perovskites are good candidates for ferroelectric material.By building functional inorganic frameworks,organic-inorganic hybrid perovskites can combine ferroelectricity with other interesting properties such as magnetic,photoluminescence,and semiconducting property within a single molecular composite.Although the power conversion effiiencies(PCEs)of lead(Pb)halide perovskite solar cells(PVSCs)have been improved from 3.8%to 22.1%in the past few years,the developments of the more environmentally friendly tin(Sn)-based perovskite solar cells are very slow,especially for the Pb-free Sn-based PVSCs and low-bandgap mixed Sn-Pb PVSCs,of which the PCEs are still very low.Based on organic-inorganic hybrid perovskites,luminescent ferroelectrics[C4H8NH2][MnCl3]and[C4H8NH2][MnBr3](C4H8NH2 = pyrrolidinium),and ferroelectric semiconductors[C6H8CH2NH3]2[PbCl4](C6H5CH2NH3 = benzylammonium)and[CHA]2[PbBr4-4xI4x](x = 0,0.1125,0.175,CHA = cyclohexylammonium)have been successfully synthesized.The FASnI3(FA = formamidinium)Pb-free PVSCs and(FASnI3)0.6(MAPbI3)0.4(MA = methylanmonium)with a bandgap of about 1.2 eV mixed Sn-Pb PVSCs have achieved a maximum PCE of 6.22%and 15.08%,respectively.The main contents are summarized as follows.(1)In Chapter Two,[C4H8NH2][MnCl3]undergoes a ferroelectric phase transition at 295 K,with a saturation polarization of 5.5 μC/cm2.[C4H8NH2][MnBr3]exhibits a similar ferroelectric phase transition at 219 K,with a saturation polarization of 6.0 μC/cm2.The ferroelectricity is originated from the reorientation of the pyrrolidinium cation.Both[C4H8NH2][MnCl3]and[C4H8NH2][MnBr3]show intense red luminescence at about 640 nm under a UV excitation,with quantum yield of 56.7%and 28.5%,respectively.[C4H8NH2][MnBr3]also shows weak ferromagnetism.(2)In Chapter Three,[C6H5CH2NH3]2[PbCl4]has a very high Curie temperature of 438 K and large spontaneous polarization of 13 μC/cm2.The ferroelectricity can be ascribed to the reorientation of the benzylammonium cation.[C6H5CH2NH3]2[PbCl4]is also a direct bandgap semiconductor with a bandgap of 3.65 eV.[CHA]2[PbBr4]exhibits a ferroelectric phase transition at 367 K,with a saturation polarization of 5.8 μC/cm2.[CHA]2[PbBr4-4xI4x](x = 0,0.1125,0.175)have similar structure and ferroelectricity.The ferroelectricity is related to the reorientation of the cyclohexylammonium cation.[CHA]2[PbBr4-4xI4x][(x =0,0.1125,0.175)are also direct bandgap semiconductor,and the bandgap is tunable in the range of 3.05-2.74 eV with maintaining good ferroelectricity.(3)In Chapter Four,antisolvent dripping using diethyl ether together with the use of 10 mol%SnF2 additives can produce high-quality FASnI3 perovskite thin fims by one-step solution process.By using inverted planar cell architecture ofITO(indium tin oxide)/PEDOT:PSS(poly(3,4-ethylenedioxythiophene):polystyrene sulfonate)/FASnI3/C60(fullerene)/BCP(2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline)/Ag,the Pb-free FASnI3 PVSCs have achieved a maximum PCE of 6.22%.(4)In Chapter Five,by mixing stoichiometric amounts of FASnI3 and MAPbI3 perovskite precursors together with antisolvent dripping using diethyl ether and one-step solution process can obtain high-quality(FASnI3)o.6(MAPbI3)0.4(MA=methylammonium)perovskite thin fims with a bandgap of about 1.2 eV.By using inverted planar cell architecture of ITO/PEDOT:PSS/(FASnI3)0.6(MAPbI3)o.4/C60/BCP/Ag,the mixed Sn-Pb(FASnI3)0.6(MAPbI3)0.4 PVSCs have achieved a maximum PCE of 15.08%.