| Organic-inorganic hybrid metal halide perovskite materials have attracted wide attention due to their excellent photoelectric properties,adjustable band gap and solutionable preparation.The power conversion efficiency of perovskite solar cells(PSCs)has rapidly increased from the initial 3.8%to 25.5%in just a few years.At present,the photoactive layer of high-efficiency PSCs is usually a polycrystalline perovskite films prepared by a solution method,the high tolerance of perovskite materials to defects makes it possible to use low-purity materials to obtain high-performance devices.In order to further study the intrinsic properties of perovskite materials,this paper selects perovskite single crystals as the research object,and conducts research on its growth process,halogen ion exchange and stability,etc.The specific contents include:(1)Successfully grown centimeter-level(diagonal length?2 cm)MAPb X3(X=Br,I)perovskite single crystal.The common inversion crystallization method is used to grow MAPb X3single crystals,the"doll"phenomenon that may exist in crystal growth is effectively avoided by precisely control of the heating rate and the process of seed crystal transfer.The single crystal samples were characterized by powder X-ray diffractometer and high-resolution X-ray diffractometer,the rocking curve test results show that the prepared perovskite single crystal has excellent crystalline quality(full width at half maximum<0.05°).The optical properties of the obtained perovskite single crystal samples are consistent with those in the literature,the reproducible preparation of such samples provides a basis for further study of their optoelectronic properties.(2)The exchange reactions of MAPbBr3 and MAPbI3 single crystals with halogen ions in solution were studied.MAPbBr3 and MAPbI3 single crystals were immersed in MAI and MABr ethanol solutions,respectively,significant surface color changes can be observed.The halogen ion exchange reaction on the surface of single crystal was confirmed by absorption spectrum test.The reaction depth of halogen ion exchange reaction on the surface of single crystal was characterized by microscopic selective fluorescence(PL)imaging.Due to the difference of lattice parameters between MAPbBr3 and MAPbI3,the mutual substitution ability of I-and Br-is different.The penetration of I-to MAPbBr3 single crystal is up to millimeter,while the penetration of Br-to MAPbB3 single crystal is only micron.In addition,it was also observed that large-sized organic ammonium cations,such as phenyethylamine,can also be effectively embedded on the surface of MAPbI3 single crystals and form low-dimensional perovskite materials.(3)The study compared the stability of MAPbI3 single crystal,MAPbI3 polycrystalline film and MAPbI3 coated with three-layer inorganic mesoporous film(Ti O2/Zr O2/C)under high temperature and high humidity conditions.The results show that single crystal MAPbI3films have better thermal stability and humidity stability than polycrystalline MAPbI3 films.Single crystal MAPbI3 can withstand the temperature of 200°C,while polycrystalline MAPbI3 can decompose significantly in the range of 160°C to 180°C.The coating effect of the three-layer mesoporous film can effectively enhance the stability of MAPbI3 in polycrystalline form.The aging test was carried out at 180°C and 85%relative humidity,respectively,MAPbI3 deposited in the three-layer mesoporous film showed good stability. |
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