Study On Two-dimensional Perovskite Single Crystal Preparation And Photoelectric Properties

In the past decade,three dimensional（3D）lead halide perovskites APb X₃[A=CH₃NH₃⁺（MA）and Cs⁺,X=I^-,Br^-,Cl^-]have emerged as high-performance solution processable semiconductors with attractive properties,such as high absorption cross-sections and efficient photoluminescence（PL）with stoichiometric wavelength tunability,low trap state densities,and long carrier diffusion lengths.The past few years witnessed tremendous advances of organic–inorganic perovskites in solar cells,light-emitting diodes,photodetectors,and lasers.Compared with 3D counterpart,two dimensional（2D）layered perovskites with formula L₂A_n-1Pb_nX_3n+1（L=long-chain cations）naturally form organic-inorganic quantum wells（QWs）,leading to high exciton binding energy about hundreds me V and tunable band-gaps dependent on the QW thickness of n.As two-dimensional perovskite films are mixture multi-layers quantum wells and composed of nano-crystallines with numerous grain boundaries,the edge states and surface bound states play inevitable roles in their optoelectronic properties.So pure phase value n controlled 2D layered perovskite single crystals can pave the way to investigate the intrinsic properties as a function of QW thickness.Therefore,we found out two methods to fabricate value n controlled 2D layered perovskite single crystals with a variety of long-chain cations,and investigated the influence of value n to the electric and lasing properties of it.We also successfully fabricated the lead-free 2D layered perovskite single crystals,and found out it has better lasing properties than its lead counterpart.The main research contents of this article are as follows:1.We report a space-confined solution growth method to fabricate large orientation-controlled（BA）₂（MA）_n-1Pb_nX_3n+1（n=1,2,3）single crystal films with thickness about 500-1000nm.Then we use the classical mechanically exfoliated protocol to control the thickness mainly<250nm.In the end,we successfully integrated our exfoliated（BA）₂（MA）_n-1Pb_nX_3n+1（n=1,2,3）single crystals in a metal-semiconductor-metal photodetector and investigate the photo detective properties of it at ambient condition,which shows the responsivity of 2.96A/W,detectivity of 10¹³jones,dark current as low as 10^-14A,on/off ratio reaching 2862.2.We report a facile solution growth method for fabricating single-crystalline flakes（SFCs）of（PEA）₂（MA）_n-1Pb_nI_3n+1(PEA=phenylethylammonium,...