Communication Cite This: J. Am. Chem. Soc. 2017, 139, 15592-15595
pubs.acs.org/JACS
Directional Growth of Ultralong CsPbBr3 Perovskite Nanowires for High-Performance Photodetectors Muhammad Shoaib,†,§ Xuehong Zhang,†,§ Xiaoxia Wang,†,§ Hong Zhou,† Tao Xu,‡ Xiao Wang,† Xuelu Hu,† Huawei Liu,† Xiaopeng Fan,† Weihao Zheng,† Tiefeng Yang,† Shuzhen Yang,† Qinglin Zhang,† Xiaoli Zhu,† Litao Sun,‡ and Anlian Pan*,† †
Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, State Key Laboratory of Chemo/Biosensing and Chemometrics, and School of Physics and Electronic Science, Hunan University, Changsha 410082, China ‡ SEU-FEI Nano-Pico Center, Key Lab of MEMS of Ministry of Education, Southeast University, Nanjing 210096, China S Supporting Information *
of all-inorganic perovskites is difficult due to the lower solubility of inorganic perovskites and more complex Cs−Pb−X phase diagram.22 Graphoepitaxial effect assisted vapor growth is welldeveloped to realize growth of horizontal and aligned semiconductor NWs on sapphire substrates with well-aligned nanosteps or grooves, which can provide a maximum interface area between the substrate and the NWs, resulting in the directional and continuous growth of the NWs.23−27 Here, we report the successful vapor growth of ultralong directional CsPbBr3 perovskite NWs using the graphoepitaxial effect on annealed M-plane sapphire substrates. The wires are well-aligned along the groove direction of the substrate, with lengths up to several millimeters, demonstrating the longest CsPbX3 NWs reported so far. Microstructure characterizations demonstrate the high-quality single-crystal nature of the achieved wires, which was further revealed by the strong light emission and excellent optical waveguiding. High-performance photodetectors were achieved based on individual CsPbBr3 NWs, which have a responsivity of 4400 A/W and a response speed of 252 μs, much higher than that of all previously reported photodetectors on single halide perovskite nano/microstructures.28−36 This study makes an important step toward large-scale preparation of wellaligned perovskite NWs for applications in high-density optoelectronic devices and on-chip integrated photonics systems. To grow directional perovskite NWs, a mixture of CsBr and PbBr2 powders (molar ratio 2:1) was placed at the center of heating zone of a quartz tube. Before the growth, several annealed M-plane sapphire sheets with aligned V-shaped nanogrooves at the surface were placed downstream as the growth substrates. At the same time, high-purity N2 gas was introduced into the quartz tube at 60 sccm. During the growth, the furnace was rapidly heated to 600 °C and maintained this temperature for 10 min, with the pressure inside the tube kept at ∼760 Torr (normal pressure). Next, the furnace was naturally cooled to room temperature. A large number of directional and ultralong NWs on the sapphire surface were obtained after the growth. Figure 1a shows the typical low-magnification scanning electron microscope (SEM) image of the collected sample, which exhibits a large area of perfectly aligned CsPbBr3 NWs, with lengths of up to several millimeters. The inset shows the
ABSTRACT: Directional growth of ultralong nanowires (NWs) is significant for practical application of large-scale optoelectronic integration. Here, we demonstrate the controlled growth of in-plane directional perovskite CsPbBr3 NWs, induced by graphoepitaxial effect on annealed M-plane sapphire substrates. The wires have a diameter of several hundred nanometers, with lengths up to several millimeters. Microstructure characterization shows that CsPbBr3 NWs are high-quality single crystals, with smooth surfaces and well-defined cross section. The NWs have very strong band-edge photoluminescence (PL) with a long PL lifetime of ∼25 ns and can realize highquality optical waveguides. Photodetectors constructed on these individual NWs exhibit excellent photoresponse with an ultrahigh responsivity of 4400 A/W and a very fast response speed of 252 μs. This work presents an important step toward scalable growth of high-quality perovskite NWs, which will provide promising opportunities in constructing integrated nanophotonic and optoelectronic systems.
I
norganic semiconductor perovskite CsPbX3 (X = Cl, Br, I) nanostructures have attracted tremendous attention for developing novel light-emitting diodes, lasers, and photodetectors, due to their extraordinary optoelectronic properties.1−7 Though CsPbX3 quantum dots, nanoplates, and nanowires (NWs) have been realized by solution-based methods,8−11 conventional chemical vapor deposition, generally exploited to grow high-quality electronic materials, may offer an alternative pathway to achieve high-quality all-inorganic perovskite nanostructures. Many efforts have recently been devoted to realize the growth of perovskite CsPbX3 nanostructures using the vapor route, including single-crystalline nanoplates, nanowire networks, and nano/microrods.12−17 Large-scale growth or assembly of semiconductor NWs with horizontal alignment on surfaces is highly desirable in future integrated devices.18−20 Growth of directional and ultralong CsPbX3 NWs is an important step in their integration into practical devices but still remains challenging. Recently, ultralong organic−inorganic perovskite wires were synthesized via template-assisted solution methods.21 However, solution growth © 2017 American Chemical Society
Received: August 18, 2017 Published: October 23, 2017 15592
DOI: 10.1021/jacs.7b08818 J. Am. Chem. Soc. 2017, 139, 15592−15595
Communication
Journal of the American Chemical Society
between the NW and V-shaped nanogroove.23 The measured lattice spacings of the NW are approximately 0.59 and 0.58 nm, corresponding to (001) and (010) lattice planes of monoclinic perovskite CsPbBr3.38 The corresponding fast Fourier transform pattern shows clear diffraction spots from both the substrate (red) and CsPbBr3 NW (cyan), demonstrating that the directional NW is a high-crystallinity structure with axial growth along the [100] direction (Figure 2d).19 The formed NW with triangular cross section is also thermodynamically favorable by exposing the (100) surfaces with low surface energy.19,33 SEM, XRD, and TEM results demonstrate that the directional and ultralong high-quality CsPbBr3 NWs were successfully achieved along the nanogrooves on the annealed M-plane sapphire. Formation of these directional and ultralong CsPbBr3 NWs can be understood from the following aspects. The vapor precursors first deposit and graphoepitaxially nucleate at the Vshaped nanogrooves of the sapphire substrate, as revealed by the HRTEM in Figure 2c,23 to form CsPbBr3 nanocrystal seeds, which will further grow into 1D nanostructures along (100) planes with low surface energy.19,33 Due to the existence of nanogrooves, NW growth is realized directionally with [100] orientation along the V-shaped nanogrooves via graphoepitaxial effect driven by the maximum interface area between the substrate and NW.23−27 This is quite different from the observed orientational random growth of micro/nanorods on SiO2/Si substrate.19 It is interesting to find that a high growth pressure plays a key role in realizing the ultralong growth of the directional CsPbBr3 NWs. Comparison experiments at low pressure (∼300 Torr) demonstrate that only microwires with larger diameter (2− 5 μm) are obtained, with their ultimate length
