Single‐crystalline perovskites are ideal candidates for lasing and other optoelectronic applications. Although significant efforts have been made to grow both bulk single‐crystalline perovskites in liquid solution, their dimensions are still too large to make nanoscale whispering‐gallery‐mode (WGM) resonator based lasers that possess high quality (Q) factor and small volume. Besides, most reported perovskite resonators do not possess atomically smooth surfaces and facets, which limits the Q and thereby increases the lasing threshold. Here, atomically smooth triangular PbI2 templates are fabricated on a mica substrate by the vapor phase deposition method and are converted to atomically smooth perovskites which have regular and unwrinkled facets with average surface roughness less than 2 nm. By using a CH3NH3PbI3 nanoplatelet with a side length of 27 µm and thickness of 80 nm, room temperature WGM lasing with a Q up to 2600 is demonstrated, the highest reported for hybrid organic–inorganic perovskite nanoplatelets. In addition, the volume of the WGM mode is reduced significantly in comparison with the prior reports. The realized high‐quality triangular CH3NH3PbI3 perovskite nanoplatelets with high Q factor and small volume are expected to perform as ideal cavities for long pulse durations lasers and would find potential applications in integrated optoelectronic devices.

Record-Low-Threshold Lasers Based on Atomically Smooth Triangular Nanoplatelet Perovskite

Lead halide perovskites are promising optoelectronic materials due to their unique properties such as strong light absorption, high carrier mobility, easily tunable bandgap, and compatibility with solution processable techniques. Most of the perovskite photodetectors are made of polycrystalline films, which are inferior due to large defective grain boundaries with respect to their single-crystalline (SC) counterparts. We have successfully grown SC lead halide perovskite wafers as large as 10 mm by combining the space-confined growth and seed-induced crystallization methods. In contrast, the single space-confined growth method only produces multiple SCs with sizes smaller than 3 mm. Due to the absence of grain-boundaries, the trap density of the prepared large SC perovskite wafer is only 2.36 × 1010 cm−3, much lower than that of polycrystalline thin films. The photodetectors based on the SC perovskite wafer with excellent crystalline quality show a light on/off current ratio of 4.3 × 103, a response time of 770 μs, and a linear dynamic range of 119 dB. At the lowest detectable illumination power density of 80 nW cm−2, the prepared photodetector shows the highest external quantum efficiency, responsivity and detectivity of 904%, 3.87 A W−1, and 1.77 × 1013 Jones, respectively. Moreover, a natural SC perovskite device without any modification possesses good stability with its photocurrent maintained above 80% of its original value after 30 days of storage in air. The results indicate that high-performance photodetectors based on SC perovskite wafers may become competitive in future semiconductor information applications.

Single-crystalline lead halide perovskite wafers for high performance photodetectors

Solution-processable, single-crystalline perovskite nanowires are ideal candidates for developing low-cost photodetectors, but their detectivities are limited due to a high level of unintentional defects. Through the surface-initiated solution-growth method, we fabricated high-quality, single-crystalline, defects-suppressed MAPbI3 nanowires, which possess atomically smooth side surfaces with a surface roughness of 0.27 nm, corresponding to a carrier lifetime of 112.9 ns. By forming ohmic MAPbI3/Au contacts through the dry contact method, high-performance metal–semiconductor–metal photodetectors have been demonstrated with a record large linear dynamic range of 157 dB along with a record high detectivity of 1.2×1014  Jones at an illumination power density of 5.5  nW/cm2. Such superior photodetector performance metrics are attributed to, first, the defects-suppressed property of the as-grown MAPbI3 nanowires, which leads to a quite low noise current in the dark, and second, the ohmic contact between MAPbI3 and Au interfaces, which gives rise to an improved responsivity compared with the Schottky contact counterpart. The realized high-performance MAPbI3 nanowire photodetector advances the development of low-cost photodetectors and has potential applications in weak-signal photodetection.

High detectivity photodetectors based on perovskite nanowires with suppressed surface defects

As a potential candidate for modern optoelectronics, two-dimensional PbI2 nanosheets have received much attention. In this paper, we report a simple, low-cost cooling supersaturated aqueous solutio...

PbI2 Nanosheets for Photodetectors via the Facile Cooling Thermal Supersaturation Solution Method

2H-type lead iodide (PbI2) is a two-dimensional (2D) layered semiconductor and has recently received considerable attention as a precursor for lead halide perovskite solar cells. Although the pressure-induced structural phase transitions of PbI2 have been investigated for several decades, the detailed crystalline structure of PbI2 at high pressure is still elusive because of lacking in situ x-ray diffraction (XRD) studies. In this report, in situ Raman spectra and XRD patterns of 2H-PbI2 under pressure have been investigated in a diamond-anvil cell. Both Raman spectra and XRD patterns provide consistent evidence for two structural phase transitions upon compression at approximately 0.58 and 2.6 GPa. The XRD patterns suggest that the complete pressure-driven phase transition sequence of PbI2 up to 20 GPa is two-dimensional hexagonal 2H- P3¯m1→polytype 4H-P3m1→three-dimensional (3D) orthorhombic Pnma. The uncovered 2D to 3D structural transition in 2H-PbI2 advances the understanding of structural stability of 2H-type layered semiconductors and lead halide perovskite. 

Pressure-induced two-dimensional to three-dimensional structural phase transition in 2H-type layered lead iodide PbI2

In this work, the synthesis of regular single crystalline lead iodide nanoplatelets are carried out based on the physical vapor phase deposition method. Different lead iodide nanoplatelets are obtained by tuning the location of the mica substrate along with the temperature of the tube furnace. The rules of size, thickness, density of the lead iodide nanoplatelets at varied deposition conditions are analyzed according to the crystal growth principles. It was claimed in literature that the photoluminescence of lead iodide could be obtained only at a low temperature (lower than 200 K). Here, at room temperature, we successfully obtained the photoluminescence spectra of the prepared lead iodide nanoplatelets, which possess two apparent peaks due to the biexcitons and the inelastic scattering of excitons, respectively. Our present study contributes to the development of nanoscaled high performance optoelectronic devices.

Controllable deposition of regular lead iodide nanoplatelets and their photoluminescence at room temperature

The invention belongs to the technical field of design and preparation of a mini-type laser resonant cavity and particularly relates to a metal halide perovskite mono-crystal micro-cavity and a production method thereof. A methylamine lead-iodide perovskite mono-crystal micro-cavity takes a mica sheet as a substrate, and methylamine lead-iodide perovskite is deposited to form the mono-crystal micro-cavity; the shape is a regular triangular or hexagonal nano-sheet; and the size of the edge of a triangular shape or a hexagonal shape is 3-15 microns, and the thickness is 50-100 nanometers. The invention further relates to the production method. In the second step of vapor phase deposition (a process of converting a lead halide crystal to a perovskite crystal), any inert gas is not introduced, and preparation of a perovskite crystal is finished through a standing and evaporating method.

Methylamine lead-iodide perovskite mono-crystal micro-cavity and production method thereof

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Controllable deposition of regular lead iodide nanoplatelets and their photoluminescence at room temperature

Methylamine lead-iodide perovskite mono-crystal micro-cavity and production method thereof