Cheng Chen

Bio: Cheng 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 16, co-authored 24 publications receiving 2718 citations.

Brightly Luminescent and Color-Tunable Colloidal CH3NH3PbX3 (X = Br, I, Cl) Quantum Dots: Potential Alternatives for Display Technology.

Abstract: Organometal halide perovskites are inexpensive materials with desirable characteristics of color-tunable and narrow-band emissions for lighting and display technology, but they suffer from low photoluminescence quantum yields at low excitation fluencies. Here we developed a ligand-assisted reprecipitation strategy to fabricate brightly luminescent and color-tunable colloidal CH3NH3PbX3 (X = Br, I, Cl) quantum dots with absolute quantum yield up to 70% at room temperature and low excitation fluencies. To illustrate the photoluminescence enhancements in these quantum dots, we conducted comprehensive composition and surface characterizations and determined the time- and temperature-dependent photoluminescence spectra. Comparisons between small-sized CH3NH3PbBr3 quantum dots (average diameter 3.3 nm) and corresponding micrometer-sized bulk particles (2–8 μm) suggest that the intense increased photoluminescence quantum yield originates from the increase of exciton binding energy due to size reduction as well a...

Broadband Black-Phosphorus Photodetectors with High Responsivity.

Abstract: An array of black-phosphorus photodetectors with channel lengths down to 100 nm is fabricated, and temperature-dependent photodetection measurements from 300 K down to 20 K are carried out. The devices show high photoresponse in a broadband spectral range with a record-high photoresponsivity of 4.3 × 10(6) A W(-1) at 300 K for the 100 nm device.

Optical properties of amorphous and polycrystalline Sb2Se3 thin films prepared by thermal evaporation

Abstract: Sb2Se3 is a very promising photovoltaic material because of its attractive material, optical and electrical properties. Very recently, we reported a superstrate CdS/Sb2Se3 solar cell with 5.6% certified efficiency. In this letter, we focused on the optical properties of amorphous and polycrystalline Sb2Se3 thin films prepared by thermal evaporation. Using temperature dependent transmission spectrum and temperature dependent photoluminescence, the indirect optical transition nature and bandgap values as functions of temperature were acquired. Using ellipsometry measurements and Swanepoel's envelope method, the refractive indices as well as the dielectric constant in a wide wavelength range of 193–2615 nm were obtained. These works would lay the foundation for the further development of Sb2Se3 thin film solar cells.

10% Efficiency Cu2ZnSn(S,Se)4 thin film solar cells fabricated by magnetron sputtering with enlarged depletion region width

Abstract: High performance Cu2ZnSn(S,Se)4 (CZTSSe) solar cells are fabricated by selenization of the precursor films of Mo/Sn/Cu/ZnS/Sn/ZnS/Cu deposited by magnetron sputtering. The investigation of the solar cells with different Zn/Sn ratio in CZTSSe film discloses that the charge carrier concentration and depletion region width of the device is very sensitive to Zn/Sn ratio of CZTSSe layer. The CZTSSe film with Zn/Sn=1.05 has lower carrier density (5.0×1015 cm−3), which is half of the cell with Zn/Sn=1.12, whereas the depletion region at the CdS/CZTSSe hetero-junction interface of the former (200–250 nm) is 100 nm longer than the latter. As a result, better collection of photo-generated charge carrier is found with the cell with longer Wd in the longer wavelength region above 800 nm. Therefore, the average power conversion efficiency is increased from 6.53% to 9.16% with enlarged depletion region width, and the best performance with 10.2% efficiency is achieved.

Quantum Dot Light-Emitting Diodes Based on Inorganic Perovskite Cesium Lead Halides (CsPbX3)

Abstract: Novel quantum-dot light-emitting diodes based on all-inorganic perovskite CsPbX3 (X = Cl, Br, I) nanocrystals are reported. The well-dispersed, single-crystal quantum dots (QDs) exhibit high quantum yields, and tunable light emission wavelength. The demonstration of these novel perovskite QDs opens a new avenue toward designing optoelectronic devices, such as displays, photodetectors, solar cells, and lasers.

Quantum dot-induced phase stabilization of α-CsPbI3 perovskite for high-efficiency photovoltaics.

Abstract: We show nanoscale phase stabilization of CsPbI 3 quantum dots (QDs) to low temperatures that can be used as the active component of efficient optoelectronic devices. CsPbI 3 is an all-inorganic analog to the hybrid organic cation halide perovskites, but the cubic phase of bulk CsPbI 3 (α-CsPbI 3 )—the variant with desirable band gap—is only stable at high temperatures. We describe the formation of α-CsPbI 3 QD films that are phase-stable for months in ambient air. The films exhibit long-range electronic transport and were used to fabricate colloidal perovskite QD photovoltaic cells with an open-circuit voltage of 1.23 volts and efficiency of 10.77%. These devices also function as light-emitting diodes with low turn-on voltage and tunable emission.

CsPbX3 Quantum Dots for Lighting and Displays: Room-Temperature Synthesis, Photoluminescence Superiorities, Underlying Origins and White Light-Emitting Diodes

Abstract: Recently, Kovalenko and co-workers and Li and co-workers developed CsPbX3 (X = Cl, Br, I) inorganic perovskite quantum dots (IPQDs), which exhibited ultrahigh photoluminescence (PL) quantum yields (QYs), low-threshold lasing, and multicolor electroluminescence. However, the usual synthesis needs high temperature, inert gas protection, and localized injection operation, which are severely against applications. Moreover, the so unexpectedly high QYs are very confusing. Here, for the first time, the IPQDs' room-temperature (RT) synthesis, superior PL, underlying origins and potentials in lighting and displays are reported. The synthesis is designed according to supersaturated recrystallization (SR), which is operated at RT, within few seconds, free from inert gas and injection operation. Although formed at RT, IPQDs' PLs have QYs of 80%, 95%, 70%, and FWHMs of 35, 20, and 18 nm for red, green, and blue emissions. As to the origins, the observed 40 meV exciton binding energy, halogen self-passivation effect, and CsPbX3@X quantum-well band alignment are proposed to guarantee the excitons generation and high-rate radiative recombination at RT. Moreover, such superior optical merits endow them with promising potentials in lighting and displays, which are primarily demonstrated by the white light-emitting diodes with tunable color temperature and wide color gamut.

Tuning the Optical Properties of Cesium Lead Halide Perovskite Nanocrystals by Anion Exchange Reactions

Abstract: We demonstrate that, via controlled anion exchange reactions using a range of different halide precursors, we can finely tune the chemical composition and the optical properties of presynthesized colloidal cesium lead halide perovskite nanocrystals (NCs), from green emitting CsPbBr3 to bright emitters in any other region of the visible spectrum, and back, by displacement of Cl– or I– ions and reinsertion of Br– ions. This approach gives access to perovskite semiconductor NCs with both structural and optical qualities comparable to those of directly synthesized NCs. We also show that anion exchange is a dynamic process that takes place in solution between NCs. Therefore, by mixing solutions containing perovskite NCs emitting in different spectral ranges (due to different halide compositions) their mutual fast exchange dynamics leads to homogenization in their composition, resulting in NCs emitting in a narrow spectral region that is intermediate between those of the parent nanoparticles.

Low-threshold amplified spontaneous emission and lasing from colloidal nanocrystals of caesium lead halide perovskites

Abstract: Metal halide semiconductors with perovskite crystal structures have recently emerged as highly promising optoelectronic materials. Despite the recent surge of reports on microcrystalline, thin-film and bulk single-crystalline metal halides, very little is known about the photophysics of metal halides in the form of uniform, size-tunable nanocrystals. Here we report low-threshold amplified spontaneous emission and lasing from ∼10 nm monodisperse colloidal nanocrystals of caesium lead halide perovskites CsPbX3 (X=Cl, Br or I, or mixed Cl/Br and Br/I systems). We find that room-temperature optical amplification can be obtained in the entire visible spectral range (440–700 nm) with low pump thresholds down to 5±1 μJ cm−2 and high values of modal net gain of at least 450±30 cm−1. Two kinds of lasing modes are successfully observed: whispering-gallery-mode lasing using silica microspheres as high-finesse resonators, conformally coated with CsPbX3 nanocrystals and random lasing in films of CsPbX3 nanocrystals. Lead halide perovskite colloidal nanocrystals have promising optoelectronic properties, such as high photoluminescence quantum yields and narrow emission linewidths. Here, the authors report low-threshold amplified spontaneous emission and two kinds of lasing in nanostructured caesium lead halide perovskites.