Zhuo Chen

Bio: Zhuo Chen is an academic researcher from Huazhong University of Science and Technology. The author has contributed to research in topics: Photoluminescence & Perovskite (structure). The author has an hindex of 3, co-authored 4 publications receiving 33 citations.

Direct synthesis of cubic phase CsPbI3 nanowires

Abstract: One-dimensional all-inorganic halide perovskites have emerged as one of the most prominent materials in the application of optoelectronic devices due to their remarkable properties such as a low number of defects, morphological anisotropy, mechanical flexibility and fast charge transfer capability. Particularly, cubic (α) phase CsPbI3 has the narrowest band gap of 1.73 eV among all-inorganic lead halide perovskites, exhibiting the greatest potential in solar cell applications. However, the direct synthesis of room temperature stabilized α-CsPbI3 nanowires is challenging and remains unfulfilled because the synthesis reaction usually involves a phase change process, resulting in an undesired orthorhombic (δ) phase with a wider bandgap of 2.82 eV. Here, we report a low-temperature approach to directly synthesize highly stabilized α-CsPbI3 nanowires. Low reaction temperature, capping ligand protection, and extended growth time are employed to successfully grow α-CsPbI3 nanowires. The as-synthesized α-CsPbI3 nanowires are 10–20 μm in length and 5–80 nm in diameter. The X-ray diffraction (XRD), photoluminescence (PL), and UV-vis absorption results verify that these cubic phase nanowires maintain excellent stability at room temperature for 90 days. The CsPbI3 nanowires show a PL peak located at around 685 nm and the UV-vis absorption spectrum further reveals that the band gap is about 1.77 eV. The excellent optical properties of the phase-stable CsPbI3 nanowires offer great potential in the field of optoelectronic devices.

Cu2+-Doped CsPbI3 Nanocrystals with Enhanced Stability for Light-Emitting Diodes.

Abstract: Black phase CsPbI3 perovskites have emerged as one of the most promising materials for use in optoelectronic devices due to their remarkable properties. However, black phase CsPbI3 usually possesses poor stability and involves a phase change process, resulting in an undesired orthorhombic (δ) yellow phase. Here, the enhanced stability of CsPbI3 nanocrystals is achieved by incorporating the Cu2+ ion into the CsPbI3 lattice under mild conditions. In particular, the Cu2+-doped CsPbI3 film can maintain red luminescence for 35 days in air while the undoped ones transformed into the nonluminescent yellow phase in several days. Furthermore, first-principles calculations verified that the enhanced stability is ascribed to the increased formation energy due to the successful doping of Cu2+ in CsPbI3. Benefiting from such an effective doping strategy, the as-prepared Cu2+-doped CsPbI3 as an emitting layer shows much better performance compared with that of the undoped counterpart. The turn-on voltage of the Cu2+-doped quantum-dot light-emitting diode (QLED) (1.6 V) is significantly reduced compared with that of the pristine QLED (3.8 V). In addition, the luminance of the Cu2+-doped QLED can reach 1270 cd/m2, which is more than twice that of the pristine CsPbI3 QLED (542 cd/m2). The device performance is believed to be further improved by optimizing the purification process and device structure, shedding light on future applications.

Gram-scale synthesis of all-inorganic perovskite quantum dots with high Mn substitution ratio and enhanced dual-color emission

Abstract: Mn-doped all-inorganic perovskite quantum dots (QDs) provide prominent applications in the fields of low-cost light source or display, because of their remarkable properties including dual-color emission and reduced lead content, as well as high photoluminescence quantum yields (PLQYs) and high stability. However, the existing synthesis approaches usually require hash conditions, such as high temperature and nitrogen protection, which is a major hurdler for the practical manufacturing. In addition, the significantly high Mn substitution ratio in CsPbX3 QDs is still challenging. The real dual-color emission with two strong emission peaks in the Mn-doped all-inorganic perovskite QDs has attracted great interest. Here we present a gram-scale approach to synthesize both CsPbxMn1−xCl3 and CsPb1−xMnxClyBr3−y QDs at 100 °C in the air with high Mn substitution ratio, up to 55.64% atomically. The as-prepared CsPb1−xMnxClyBr3−y QDs exhibit high PLQYs of 62.41% and dual-color emission with two strong emission peaks around at 400–450 nm and 600 nm, respectively. The enhanced peak at 400–450 nm is a result of the hybrid halides in CsPbBrxCl3−x host. Furthermore, the unique advantage of the optical emission and high PLQYs properties of the CsPbxMn1−xCl3 QDs has been demonstrated as invisible ink for encryption applications and polymer composites. Our gram-scale synthesis approach for Mn-doped all-inorganic perovskite QDs may boost the future research and practical applications of QDs-based white LED, spintronics, and molecular barcoding.

Synthesis of highly luminescent Mn-doped CsPbCl3 nanoplatelets for light-emitting diodes

Abstract: Two-dimensional all-inorganic halide perovskites (CsPbX3, X = Cl, Br or I) have emerged as prominent materials due to their unique properties, including ultrathin thickness in high surface area for catalysis, good mechanical flexibility for flexible electronics/optoelectronics, and high charge extraction and transport for photodetectors. However, the high luminescence of two-dimensional Mn-doped CsPbX3 that is crucial to light-emitting diodes and display applications remains unfulfilled. The existing synthesis approaches of two-dimensional Mn-doped CsPbX3 usually result in low luminescence because of either low solubility of precursors at low temperature or high concentrated nanocubes at high temperature (e.g. 180 °C). Herein, we report a moderate-temperature and atmospheric approach to synthesize highly luminescent Mn-doped CsPbCl3 nanoplatelets with only 4 monolayers. Different Mn–Pb feed ratios are explored to study the morphology evolution from nanocubes to nanoplatelets and the corresponding influence of two emission peaks at around 400 nm and 600 nm. The photoluminescence quantum yield (PLQY) of our Mn-doped CsPbCl3 nanoplatelets is up to 53.76%, which is the highest reported value in Mn-doped two-dimensional all-inorganic halide perovskites. The nanoplatelets exhibit excellent stability at room temperature in air (over 60 days). For the first time, both orange-red and warm white light-emitting diodes (LEDs) have been achieved through the nanoplatelets as the color conversion materials. Moreover, flexible composite fluorescent polymer films based on the nanoplatelets are demonstrated with high luminescence and stability (over 6 months), which indicate prominent potential in flexible displays.

Fabrication of ZnO dual electron transport layer via atomic layer deposition for highly stable and efficient CsPbBr3 perovskite nanocrystals light-emitting diodes

Abstract: Electron transport layers (ETLs) are important components of high-performance all-inorganic perovskite nanocrystals light-emitting diodes (PNCs-LED). Herein, atomic layer deposition (ALD) of inorganic ZnO layer is combined to the organic 1,3,5-Tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi) to form dual ETLs to enhance both the efficiency and stability of PNCs-LED simultaneously. Optimization of ZnO thickness suggested that 10 cycles ALD yields the best performance of the devices. The external quantum efficiency of the device reaches to 7.21% with a low turn-on voltage (2.4 V). Impressively, the dual ETL PNCs-LED realizes maximum T 50 lifetime of 761 h at the initial luminance of 100 nit, which is one of the top lifetimes among PNCs-LEDs up to now. The improved performance of dual ETL PNCs-LED is mainly due to the improved charge transport balance with favorable energy level matching. These findings present a promising strategy to modify the function layer via ALD to achieve both highly efficient and stable PNCs-LED.

Colloidal Metal‐Halide Perovskite Nanoplatelets: Thickness‐Controlled Synthesis, Properties, and Application in Light‐Emitting Diodes

Abstract: Colloidal metal-halide perovskite nanocrystals (MHP NCs) are gaining significant attention for a wide range of optoelectronics applications owing to their exciting properties, such as defect tolerance, near-unity photoluminescence quantum yield, and tunable emission across the entire visible wavelength range. Although the optical properties of MHP NCs are easily tunable through their halide composition, they suffer from light-induced halide phase segregation that limits their use in devices. However, MHPs can be synthesized in the form of colloidal nanoplatelets (NPls) with monolayer (ML)-level thickness control, exhibiting strong quantum confinement effects, and thus enabling tunable emission across the entire visible wavelength range by controlling the thickness of bromide or iodide-based lead-halide perovskite NPls. In addition, the NPls exhibit narrow emission peaks, have high exciton binding energies, and a higher fraction of radiative recombination compared to their bulk counterparts, making them ideal candidates for applications in light-emitting diodes (LEDs). This review discusses the state-of-the-art in colloidal MHP NPls: synthetic routes, thickness-controlled synthesis of both organic-inorganic hybrid and all-inorganic MHP NPls, their linear and nonlinear optical properties (including charge-carrier dynamics), and their performance in LEDs. Furthermore, the challenges associated with their thickness-controlled synthesis, environmental and thermal stability, and their application in making efficient LEDs are discussed.

Unveiling the Excited-State Dynamics of Mn2+ in 0D Cs4PbCl6 Perovskite Nanocrystals

Abstract: Doping is an effective strategy for tailoring the optical properties of 0D Cs4PbX6 (X = Cl, Br, and I) perovskite nanocrystals (NCs) and expanding their applications. Herein, a unique approach is reported for the controlled synthesis of pure-phase Mn2+-doped Cs4PbCl6 perovskite NCs and the excited-state dynamics of Mn2+ is unveiled through temperature-dependent steady-state and transient photoluminescence (PL) spectroscopy. Because of the spatially confined 0D structure of Cs4PbCl6 perovskite, the NCs exhibit drastically different PL properties of Mn2+ in comparison with their 3D CsPbCl3 analogues, including significantly improved PL quantum yield in solid form (25.8%), unusually long PL lifetime (26.2 ms), large exciton binding energy, strong electron-phonon coupling strength, and an anomalous temperature evolution of Mn2+-PL decay from a dominant slow decay (in tens of ms scale) at 300 K to a fast decay (in 1 ms scale) at 10 K. These findings provide fundamental insights into the excited-state dynamics of Mn2+ in 0D Cs4PbCl6 NCs, thus laying a foundation for future design of 0D perovskite NCs through metal ion doping toward versatile applications.

CsPbI3 Nanotube Photodetectors with High Detectivity.

Abstract: In the present work, the exploration of photodetectors (PDs) based on CsPbI3 nanotubes are reported. The as-prepared CsPbI3 nanotubes can be stable for more than 2 months under air conditions. It is found that, in comparison to the nanowires, nanobelts, and nanosheets, the nanotubes can be advantageous to be used as the functional units for PDs, which is mainly attributed to the enhanced light absorption ability induced by the light trapping effect within the tube cavity. As a proof of concept, the as-constructed PDs based on CsPbI3 nanotube present an overall excellent performance with a responsivity (Rλ ), external quantum efficiency (EQE) and detectivity of 1.84 × 103 A W-1 , 5.65 × 105 % and 9.99 × 1013 Jones, respectively, which are all comparable to state-of-the-art ones for all-inorganic perovskite PDs.

Multi-modal anti-counterfeiting and encryption enabled through silicon-based materials featuring pH-responsive fluorescence and room-temperature phosphorescence

Abstract: Optical silicon (Si)-based materials are highly attractive due to their widespread applications ranging from electronics to biomedicine. It is worth noting that while extensive efforts have been devoted to developing fluorescent Si-based structures, there currently exist no examples of Si-based materials featuring phosphorescence emission, severely limiting Si-based wide-ranging optical applications. To address this critical issue, we herein introduce a kind of Si-based material, in which metal-organic frameworks (MOFs) are in-situ growing on the surface of Si nanoparticles (SiNPs) assisted by microwave irradiation. Of particular significance, the resultant materials, i.e., MOFs-encapsulated SiNPs (MOFs@SiNPs) could exhibit pH-responsive fluorescence, whose maximum emission wavelength is red-shifted from 442 to 592 nm when the pH increases from 2 to 13. More importantly, distinct room-temperature phosphorescence (maximum emission wavelength: 505 nm) could be observed in this system, with long lifetime of 215 ms. Taking advantages of above-mentioned unique optical properties, the MOFs@SiNPs are further employed as high-quality anti-counterfeiting inks for advanced encryption. In comparison to conventional fluorescence anti-counterfeiting techniques (static fluorescence outputs are generally used, thus being easily duplicated and leading to counterfeiting risk), pH-responsive fluorescence and room-temperature phosphorescence of the resultant MOFs@SiNPs-based ink could offer advanced multi-modal security, which is therefore capable of realizing higher-level information security against counterfeiting.