Organic−Inorganic Hybrid Perovskite Nanowire Laser Arrays Peng Liu,†,§ Xianxiong He,‡,§ Jiahuan Ren,‡ Qing Liao,‡ Jiannian Yao,†,‡ and Hongbing Fu*,†,‡ †
Tianjin Key Laboratory of Molecular Optoelectronic Sciences, School of Chemical Engineering and Technology, Tianjin University, and Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin 300072, P. R. China ‡ Beijing Key Laboratory for Optical Materials and Photonic Devices, Department of Chemistry, Capital Normal University, Beijing 100048, P. R. China S Supporting Information *
ABSTRACT: Fabrication of semiconductor nanowire laser arrays is very challenging, owing to difficulties in direct monolithic growth and patterning of III−V semiconductors on silicon substrates. Recently, methylammonium lead halide perovskites (MAPbX3, X = Cl, Br, I) have emerged as an important class of high-performance solution-processed optoelectronic materials. Here, we combined the “top−down” fabricated polydimethylsiloxane rectangular groove template (RGT) with the “bottom-up” solution self-assembly together to prepare large-scale perovskite nanowire (PNW) arrays. The template confinement effect led to the directional growth of MAPbX3 along RGTs into PNWs. We achieved precise control over not only the dimensions of individual PNWs (width 460−2500 nm; height 80−1000 nm, and length 10−50 μm) but also the interwire distances. Well-defined dimensions and uniform geometries enabled individual PNWs to function as high-quality Fabry−Perot nanolasers with almost identical optical modes and similarly low-lasing thresholds, allowing them to ignite simultaneously as a laser array. Optical tests demonstrated that PNW laser arrays exhibit good photostabillity with an operation duration exceeding 4 × 107 laser pulses. Precise placement of PNW arrays at specific locations makes our method highly compatible with lithographic techniques, which are important for integrating PNW electronic and photonic circuits. KEYWORDS: lead halide perovskite, templated solution-growth, nanowire array, nanowire laser, nanophotonics field-assisted assembly, laminar flow in microfluidic channels, and so on, still have not achieved high yield, good reproducibility, and high-precision addressability.15 Therefore, the search for cost-effective, massively scalable fabrication of SNW laser arrays is of both fundamental and practical importance. Methylammonium lead halide perovskites (MAPbX3 with MA = CH3NH3 cations and X = Cl, Br, I anions) have recently emerged as an important class of high-performance solutionprocessed semiconductors16−18 with a record-high photovoltaic efficiency of 22.1% in solar cells19 and an external quantum efficiency of up to 11.7% in light-emitting diodes. 20 Furthermore, MAPbX3 are excellent optical-gain materials with high absorption cross sections, efficient photoluminescence (PL), long carrier diffusion lengths, and low trap-state densities.17,21−23 Very recently, single-crystal perovskite nano-
T
he imminent limitations of microelectronic chips have stimulated a great deal of research interest in the area of integrated nanophotonics.1,2 Semiconductor nanowires (SNWs) are workhorses as miniaturized building blocks for nanoscale optoelectronic devices such as field effect transistors, photovoltaic solar cells, and photodetectors.3,4 Moreover, well-faced crystalline structures of SNWs form built-in Fabry−Perot (FP) cavities for laser oscillation.5−7 Development of SNW laser arrays with outputs spanning the full visible spectrum are of great importance for full-color laser display,8 laser lighting,9 and sensing applications.10 In the past decades, a high level of composition and orientation control was achieved in the synthesis of SNWs through the hightemperature “vapor−liquid−solid” (VLS) growth.11,12 Nevertheless, assembling these SNWs into high-density and highly integrated uniform laser arrays had met with limited successes.13 On one hand, direct monolithic growth and patterning of III−V SNWs onto silicon substrate are difficult, owing to material lattice mismatch and incompatible growth temperature.14 On the other hand, postsynthesis assembly of SNWs into highly ordered arrays, such as electric- or magnetic© 2017 American Chemical Society
Received: February 25, 2017 Accepted: May 18, 2017 Published: May 18, 2017 5766
DOI: 10.1021/acsnano.7b01351 ACS Nano 2017, 11, 5766−5773
Article
www.acsnano.org
Article
ACS Nano
Figure 1. Crystal growth process and morphology of MAPbBr3 PNW arrays. (a) Schematic illustration of the preparation procedures, including steps i (solution confinement in RGTs), ii (nucleation at RGT ends), iii (one-dimensional growth along RGTs), and iv (NWL array after detachment of RGTs). (b) Low- (left), medium- (middle), and high-magnification (right) images of MAPbBr3 PNW arrays. (c) AFM image of the MAPbBr3 PNW on silicon substrate.
precise control over the widths (W = 460−2500 nm) and lengths (L = 10−50 μm) of individual PNWs as well as the interwire distances. Meanwhile, the height of PNW (H = 80− 1000 nm) was controlled by the concentration of the stock solution. We found that well-defined dimensions and uniform geometries enabled individual PNWs to function as high-quality FP lasers with almost identical optical modes and similarly low lasing thresholds, allowing igniting them simultaneously as a laser array. We believe that precisely placing of PNW arrays at specific locations, when combined with lithographic techniques, could be promising for integrating PNW electronic and photonic circuits.
wire (PNW) lasers were demonstrated with very low lasing thresholds (220 nJ/cm2) and high quality factors (Q ∼ 3600), which were solution grown by exposing a lead acetate film to a solution of methylammonium halide salt.24 Following this preparation protocol, PNW lasers of formamidinium (FAPbX3)25 and cesium lead halide perovskites (CsPbX3)26,27 were further reported. Because these PNWs were grown on the surface of lead acetate film, they were hand-picked for lasing characterization. Note that the crystal habits of MAPbX3 generally follow platelike morphologies, especially for chlorides and bromides.28−32 Although aligned MAPbI3 microwires were reported recently using nanofluidic channels,33 blade-coating methods,34 and vapor-phase epitaxial growth methods,35 to the best of our knowledge, highly ordered arrays of PNWs with well-controlled dimensions and orientations remain grand challenges. Herein, we developed a solution-growth method to prepare PNW arrays on arbitrary substrates (such as silicon wafer or glass slide) under ambient conditions by using polydimethylsiloxane (PDMS) rectangular groove-templates (RGTs). In our method, the spatially confined template effect led to the directional growth of MAPbX3 along RGTs and therefore generated PNW arrays. By adjusting PDMS-RGTs, we achieved
RESULTS AND DISCUSSION Figure 1a illustrates the template-confined solution-growth procedures. Concave RGTs with a width of ∼1 μm, a height (or depth) of ∼5 μm, and a length varying between 10 and 50 μm (Figure S1) were fabricated using the soft lithography of PDMS.36 In the synthesis of PNW arrays, the PDMS-RGT pad (1 × 1 × 0.5 cm3) was pressed on the top of a stock solution of MAX·PbX2 (0.1 M, 20 μL) in N,N-dimethylformamide (DMF) spreading on a hydrophilic glass slide. Upon mild pressure (95% for a 1000 × 1000 μm2 array. Moreover, the size distributions of PNWs with respect to its width, height, and length are
