All‐Inorganic Perovskite Single‐Crystal Photoelectric Anisotropy

Abstract

a substantial effect on the band structure and electron behavior. Unfortunately, over past few years, most perovskite optoelectronic devices focus on polycrystalline perovskite thin-films, [10][11][12][13] and can only get the average surface-related optoelectronic properties of polycrystalline particles. The random arrangement of surface orientation in polycrystalline perovskite thin films seriously affects the carrier transportability and limits the microscopic photovoltaic performance. [14][15][16] Instead, a single-crystal-basedperovskite device can not only effectively improve photovoltaic performances due to their lower trap-state density and ultralong carrier diffusion lengths, [17][18][19] but also provide great opportunity for tailing the surface-determined optical and electronic properties. [17][18][19][20][21] However, it is still a great challenge to engineer the anisotropic surface of halide perovskite single crystals due to their ionic nature and fast crystallization during their regular solution-based growth, [22][23][24] and it is extremely difficult to quantify the surface-dependent optoelectronic properties as well as the underlying anisotropy mechanism.Herein, we report a one-step atmospheric-pressure chemical vapor deposition (APCVD) method for fabricating uniform perovskite CsPbBr 3 cube and tetrahedron single-crystals with precise control of ( 100) and ( 111) surface anisotropy, respectively (Figure S1, Supporting Information, see Methods in the Supporting Information for more synthesis details). The single-crystal-based optoelectronic devices demonstrated that the preferred (100) surface engineering of CsPbBr 3 singlecrystals enables a lowest surface bandgap energy of 2.33 eV, long carrier lifetime of 8.68 ns and high-rate carrier mobility up to 241 µm 2 V -1 s -1 , whereas the polar (111) surface induces ≈0.16 eV upward surface band bending and ultrahigh charged surface defect density of 1.49 × 10 15 cm -3 . Our results pave an ideal way to optimize the performance of halide-perovskitebased optoelectronic and/or catalysis devices by anisotropic surface engineering. Results and DiscussionScanning electron microscopy (SEM) images (Figure 1A-D) and optical microscopy images (Figures S2 and S3, Supporting Information) show that CsPbBr 3 cubes and tetrahedrons are uniform in size (≈4 µm) and monodispersed on the surface of the SiO 2 /Si substrate. The elemental distribution of Cs, Pb and Br was characterized using scanningelectron microscopy-energydispersive X-ray spectroscopy (SEM-EDS) elemental mapping, Engineering surface structure can precisely and effectively tune the optoelectronic properties of halide perovskites, but are incredibly challenging. Herein, the design and fabrication of uniform all-inorganic CsPbBr 3 cubic/tetrahedral single-crystals are reported with precise control of the ( 100) and ( 111) surface anisotropy, respectively. By combining with theoretical calculations, it is demonstrated that the preferred (100) surface engineering of the CsPbBr 3 single-crystals enables a lo...

Facet Engineering for Stable, Efficient Perovskite Solar Cells

“…(100) facet leads to a high carrier mobility of 241 μm 2 V −1 s −1 and a long carrier lifetime of 8.68 ns, whereas a low carrier mobility of 49 μm 2 V −1 s −1 and a short carrier lifetime of 5.88 ns are observed for the (111) facet. 44 Zhou and co-workers studied the (111) facet on MAPbBr 3 crystals and found that the higher MA + and [PbBr 6 ] 4− densities on the (111) plane cause a higher built-in electric field, which ultimately affects the dark current, photocurrents, and on/off ratios. 45 On the basis of this discussion, it is concluded that the shape of the perovskite crystals can be controlled by ligands and preparation methods.…”

“…The surface potentials of these two facets are also measured by Kelvin probe force microscopy, and the results show that the (100) facet exhibits an n-type behavior, whereas the (112) facet exhibits a p-type behavior . It was also demonstrated that the preferred (100) of CsPbBr 3 single crystals enables a low surface bandgap energy of 2.33 eV, and the polar (111) facet induces ∼0.16 eV upward surface-band bending . When a perovskite crystal is exposed with two facets, one facet has a lower Fermi energy level compared with the other facet, and the energy bands of adjacent facets will bend, leading to the formation of an internal electric field.…”

“…Liu and co-workers also reported that the trap density of the (100) and (111) facets of the CsPbBr 3 perovskite are 1.19 × 10 15 and 1.49 × 10 15 cm –3 , respectively. The lower trap density of the (100) facet leads to a high carrier mobility of 241 μm 2 V –1 s –1 and a long carrier lifetime of 8.68 ns, whereas a low carrier mobility of 49 μm 2 V –1 s –1 and a short carrier lifetime of 5.88 ns are observed for the (111) facet . Zhou and co-workers studied the (111) facet on MAPbBr 3 crystals and found that the higher MA + and [PbBr 6 ] 4– densities on the (111) plane cause a higher built-in electric field, which ultimately affects the dark current, photocurrents, and on/off ratios .…”

“…43 It was also demonstrated that the preferred (100) of CsPbBr 3 single crystals enables a low surface bandgap energy of 2.33 eV, and the polar (111) facet induces ∼0.16 eV upward surface-band bending. 44 When a perovskite crystal is exposed with two facets, one facet has a lower Fermi energy level compared with the other facet, and the energy bands of adjacent facets will bend, leading to the formation of an internal electric field. Furthermore, the difference between the valence band maximum (VBM) and conductive band minimum (CBM) can also influence the photogenerated exciton separation and redistribute the charge carriers between these facets.…”

Anisotropy in Perovskite Single Crystals: From Fundamentals to Applications

“…Several studies focusing on the anisotropic nature of PSCs have been reported. Especially, anisotropic light–matter interaction has been extensively studied in these perovskite single-crystalline materials. − Cho et al investigated the anisotropic response of carrier transport in the crystalline CH 3 NH 3 PbI 3 film and showed that control of crystal orientation can significantly affect the charge transport parameters . Additionally, some researchers demonstrated the anisotropic behavior of lead-halide CH 3 NH 3 PbI 3 crystals. , Furthermore, Zuo et al.…”