two-dimensional perovskite has good application prospects in solar cells laser diodes photodetectors other fields due to its high light absorption efficiency long carrier diffusion length strong light-emitting ability other advantages. Due to the non layered structure multi-phase composition it is difficult to achieve a satisfactory balance between the thickness size of perovskite by the reported preparation methods which leads to the difficulty in obtaining large-scale two-dimensional perovskite materials hinders its development in the field of optoelectronics. Chemical vapor deposition (CVD) has great potential in the preparation of two-dimensional materials. However for perovskite materials the traditional CVD method is difficult to achieve thickness reduction time-consuming. Therefore the development of a simple rapid efficient method for the preparation of two-dimensional thin-layer perovskite is of great scientific significance for the basic research practical application of two-dimensional perovskite materials. Recently Professor Zhai Tianyou of Huazhong University of science technology has developed a vapor deposition method with vertical mass transfer in the confined space realizing the controllable preparation of two-dimensional all inorganic large-scale thin-layer perovskite.
Fig. 1. Two dimensional cspbbr3 grown by vertical mass transfer in a heated plate its characterization. Key points of
1: compared with the traditional horizontal mass transfer growth method the vertical mass transfer limited space greatly reduces the uneven distribution of the source provides a more stable mass transfer environment a small mass transfer distance improves the mass transfer growth efficiency provides a stable good platform for high-quality two-dimensional perovskite growth. The typical two-dimensional perovskite optical photos (Fig. 1D) show that the size is up to 30 μ m the thickness of the thinnest nano sheet is 7.1 nm (Fig. 1E). The average thickness is ~ 14 nm (Fig. 1F). The high quality of two-dimensional perovskite nanosheets was further confirmed by spectroscopic characterization (Fig. g-h). This growth method is not only suitable for the preparation of two-dimensional perovskite but also has guiding significance for the preparation of other two-dimensional materials heterojunction.
Fig. 2. Characterization of perovskite crystal structure substrate epitaxy. Key points of
2: direct observation of the epitaxial growth relationship between 2D cspbbr3 substrate
is different from other epitaxial growth modes determined by XRD other spectroscopic means. We use high resolution TEM to directly observe the epitaxial growth relationship between 2D perovskite substrate reveal the reason for the difference of perovskite growth distribution angle. As shown in Fig. 2E the epitaxial relationship of CPB  / / mica  was observed for the first time with high resolution. In addition the common epitaxial growth relationship CPB  / / mica  shows that the perovskite mainly grows at an angle of 30 (Fig. 2C Fig. 2D). These two kinds of epitaxial relations construct the angle difference of ~ 4 ° between perovskite epitaxial nanosheets.
Fig. 3. Two dimensional perovskite spectroscopy of different components. Key points of
3: by adjusting the composition of halide elements the b gap can be continuously adjusted in the visible light b. The XRD patterns of
show that the controllable preparation of two-dimensional perovskite with different components can be realized by the substitution of different halogen components. As shown in Fig. 3b the PL spectrum shows that the b gap is continuously adjustable in the visible light b. The corresponding fluorescence lifetime also shows a significant continuous controllable property. This growth strategy with tunable b gap composition has a certain reference guiding significance for the design research of two-dimensional perovskite luminescent materials.
Fig. 4. Controllable growth of nanowires nanoplates. Key point 4 of
: the selective growth of nanowires nanosheets is realized by setting the temperature. The
studies show that the growth temperature plays a decisive role in the synthesis morphology of samples. As shown in FIG. 4A the relatively low growth temperature tends to synthesize the perovskite nanosheet structure the high growth temperature is easy to obtain the nanowire structure. Therefore the selective synthesis of nanosheets nanowires can be realized by setting the temperature. The simulation results show that at low temperature the binding energy of perovskite (001) surface substrate is lower it is easier to grow nanosheets; with the increase of temperature the binding energy of perovskite (110) surface substrate tends to be lower the stability of nanowires is enhanced which is consistent with the experimental results.
Fig. 5. Study of photodetectors based on two-dimensional perovskite. Key points of
5: high speed response (~ 20 μ s) of photodetectors based on two-dimensional perovskite nanoplates. The two-dimensional perovskites grown by
based on vertical mass transfer show excellent photoelectron properties. The samples show significant light response under 365 nm laser irradiation. As shown in Fig. 5D the dependence coefficient of photocurrent power is close to 1 which indicates that perovskite has excellent photoelectric conversion ability with detection responsivity of 1012 Jones 10-1 A / W respectively optical response switching speed of ~ 20 μ s. The high-speed photoelectric response ability provides the foundation for the application of two-dimensional perovskite in high-speed optoelectronic devices.
in conclusion a new vertical mass transfer growth method was used to realize the controllable preparation of large-scale two-dimensional all inorganic perovskite. The morphology b gap of the samples were controlled by controlling the temperature the composition respectively. Large size two-dimensional perovskite materials show excellent optoelectronic properties have a good application prospect in the field of photodetectors. This synthesis method has a certain guiding significance for the controllable preparation basic research of other two-dimensional materials their heterojunctions.
this work is currently published in small methods（ DOI:10.1002/smtd.202000102 ）It’s on.
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