Two-dimensional perovskites have demonstrated superior application prospects in optoelectronic fields,such as X^(-)ray detection,light emitting diodes,and photovoltaics,because of their tunability of band structures,i...Two-dimensional perovskites have demonstrated superior application prospects in optoelectronic fields,such as X^(-)ray detection,light emitting diodes,and photovoltaics,because of their tunability of band structures,improved stability,fast responses,and suppressed noise signal.In this work,bulk single crystals of MA_(3)Bi_(2)Br_(9)(MA^(+)=CH_(3)NH_(3)^(+))and the two mixed crystals MA_(3)Bi_(2)(Br_(0.74)I_(0.26))_(9)and MA_(3)Bi_(2)(Br_(0.62)I_(0.38))_(9)were successfully grown using the bottom-seeded solution growth method.MA_(3)Bi_(2)I_(9)crystals were also prepared and characterized for comparisons.X^(-)ray diffraction analysis revealed that all the crystals had quasitwo-dimensional(2D)structures and the partial substitution of I^(-)for Br^(-)did not alter the space group symmetry.However,with the increase of I^(-)concentrations,the incongruent melting temperature gradually decreased from 342℃for MA_(3)Bi_(2)Br_(9)to 328℃for MA_(3)Bi_(2)(Br_(0.62)I_(0.38))_(9),respectively.For the optoelectronic properties,the MA_(3)Bi_(2)Br_(9)was measured to have a direct bandgap of 2.60 eV,while the values decreased to 2.15 eV for MA_(3)Bi_(2)(Br_(0.74)I_(0.26))_(9),2.04 eV for MA_(3)Bi_(2)(Br_(0.62)I_(0.38))_(9),and 1.97 eV for MA_(3)Bi_(2)I_(9),respectively.Similarly,the photoluminescence peaks blue-shifted from 550 nm for MA_(3)Bi_(2)Br_(9),to 453 nm for MA_(3)Bi_(2)(Br_(0.74)I_(0.26))_(9),445 nm for MA_(3)Bi_(2)(Br_(0.62)I_(0.38))_(9),and 444 nm for MA_(3)Bi_(2)I_(9),respectively.Due to the strong dielectric confinement effects and anisotropic exciton transportation characteristics of the 2D structures,the targeted crystals studied all exhibited ultrafast fluorescence decay characteristics,where a decay time as short as 0.65 ns,sub-nanosecond,for MA_(3)Bi_(2)Br_(9),1.06 ns for MA_(3)Bi_(2)(Br_(0.74)I_(0.26))_(9),3.00 ns for MA_(3)Bi_(2)(Br_(0.62)I_(0.38))_(9),and 3.12 ns for MA_(3)Bi_(2)I_(9),respectively,was observed.Besides,the low-dimensional structures also brought the crystals superior environmental stability because of the suppressed ion migrations.This work provides a simple,straightforward method for the large-sized crystal growth of lowdimensional MA_(3)Bi_(2)X_(9)(X^(-)=Br^(-),I^(-)),and reveals their promising application prospects in novel optoelectronic fields.展开更多
基金support from the Innovation and Entrepreneurship Training Program for College Students(X202310452512,X202210452214).
文摘Two-dimensional perovskites have demonstrated superior application prospects in optoelectronic fields,such as X^(-)ray detection,light emitting diodes,and photovoltaics,because of their tunability of band structures,improved stability,fast responses,and suppressed noise signal.In this work,bulk single crystals of MA_(3)Bi_(2)Br_(9)(MA^(+)=CH_(3)NH_(3)^(+))and the two mixed crystals MA_(3)Bi_(2)(Br_(0.74)I_(0.26))_(9)and MA_(3)Bi_(2)(Br_(0.62)I_(0.38))_(9)were successfully grown using the bottom-seeded solution growth method.MA_(3)Bi_(2)I_(9)crystals were also prepared and characterized for comparisons.X^(-)ray diffraction analysis revealed that all the crystals had quasitwo-dimensional(2D)structures and the partial substitution of I^(-)for Br^(-)did not alter the space group symmetry.However,with the increase of I^(-)concentrations,the incongruent melting temperature gradually decreased from 342℃for MA_(3)Bi_(2)Br_(9)to 328℃for MA_(3)Bi_(2)(Br_(0.62)I_(0.38))_(9),respectively.For the optoelectronic properties,the MA_(3)Bi_(2)Br_(9)was measured to have a direct bandgap of 2.60 eV,while the values decreased to 2.15 eV for MA_(3)Bi_(2)(Br_(0.74)I_(0.26))_(9),2.04 eV for MA_(3)Bi_(2)(Br_(0.62)I_(0.38))_(9),and 1.97 eV for MA_(3)Bi_(2)I_(9),respectively.Similarly,the photoluminescence peaks blue-shifted from 550 nm for MA_(3)Bi_(2)Br_(9),to 453 nm for MA_(3)Bi_(2)(Br_(0.74)I_(0.26))_(9),445 nm for MA_(3)Bi_(2)(Br_(0.62)I_(0.38))_(9),and 444 nm for MA_(3)Bi_(2)I_(9),respectively.Due to the strong dielectric confinement effects and anisotropic exciton transportation characteristics of the 2D structures,the targeted crystals studied all exhibited ultrafast fluorescence decay characteristics,where a decay time as short as 0.65 ns,sub-nanosecond,for MA_(3)Bi_(2)Br_(9),1.06 ns for MA_(3)Bi_(2)(Br_(0.74)I_(0.26))_(9),3.00 ns for MA_(3)Bi_(2)(Br_(0.62)I_(0.38))_(9),and 3.12 ns for MA_(3)Bi_(2)I_(9),respectively,was observed.Besides,the low-dimensional structures also brought the crystals superior environmental stability because of the suppressed ion migrations.This work provides a simple,straightforward method for the large-sized crystal growth of lowdimensional MA_(3)Bi_(2)X_(9)(X^(-)=Br^(-),I^(-)),and reveals their promising application prospects in novel optoelectronic fields.
