Yousheng Zou

Improving All‐Inorganic Perovskite Photodetectors by Preferred Orientation and Plasmonic Effect

All-inorganic perovskites have high carrier mobility, long carrier diffusion length, excellent visible light absorption, and well overlapping with localized surface plasmon resonance (LSPR) of noble metal nanocrystals (NCs). The high-performance photodetectors can be constructed by means of the intrinsic outstanding photoelectric properties, especially plasma coupling. Here, for the first time, inorganic perovskite photodetectors are demonstrated with synergetic effect of preferred-orientation film and plasmonic with both high performance and solution process virtues, evidenced by 238% plasmonic enhancement factor and 106 on/off ratio. The CsPbBr3 and Au NC inks are assembled into high-quality films by centrifugal-casting and spin-coating, respectively, which lead to the low cost and solution-processed photodetectors. The remarkable near-field enhancement effect induced by the coupling between Au LSPR and CsPbBr3 photogenerated carriers is revealed by finite-difference time-domain simulations. The photodetector exhibits a light on/off ratio of more than 106 under 532 nm laser illumination of 4.65 mW cm-2 . The photocurrent increases from 0.67 to 2.77 μA with centrifugal-casting. Moreover, the photocurrent rises from 245.6 to 831.1 μA with Au NCs plasma enhancement, leading to an enhancement factor of 238%, which is the most optimal report among the LSPR-enhanced photodetectors, to the best of our knowledge. The results of this study suggest that all-inorganic perovskites are promising semiconductors for high-performance solution-processed photodetectors, which can be further enhanced by Au plasmonic effect, and hence have huge potentials in optical communication, safety monitoring, and biological sensing.

All-inorganic quantum-dot light-emitting diodes based on perovskite emitters with low turn-on voltage and high humidity stability

Recently, both light-to-electricity and electricity-to-light conversion efficiencies of perovskite achieved a breakthrough, e.g. 22.1% for solar cells and 11.7% for light-emitting diodes (LEDs), so the next fatal problem towards practical application, the device stability, became the key issue in this field. Here, we report all-inorganic LEDs including inorganic perovskite emitters (CsPbBr3) and inorganic charge transport layers (CTLs), with an emphasis on the significantly improved device stability. The quantum dot LEDs (QLEDs) were fabricated according to ITO/NiO/CsPbBr3 QDs/ZnO/Al device configuration. On the one hand, the all-inorganic LED lifetime under 65% humidity corresponding to a 70% electroluminescence (EL) conservation rate can be improved up to 3.5 times when compared with LEDs adopting conventional organic CTLs due to the intrinsic chemical stability of these inorganic CTLs and their less hydrophilic surfaces. Furthermore, as a surprise, the bare all-inorganic LED without encapsulation can work in water for about 20 seconds, which is over 10 times more sustainable than the organic–inorganic LED, which proves the excellent water-isolation ability. On the other hand, the all-inorganic QLEDs show the lowest turn-on voltage of 2.4 V among all the reported CsPbBr3 QLEDs because the inorganic CTLs possess well-matched energy band alignments with CsPbBr3, and hence result in efficient carrier injection. This work paves the way to constructing all-inorganic devices for stable perovskite photovoltaic and light-emitting devices.

High Performance Metal Halide Perovskite Light‐Emitting Diode: From Material Design to Device Optimization

Metal halide perovskites have drawn significant interest in the past decade. Superior optoelectronic properties, such as a narrow bandwidth, precise and facile tunable luminance over the entire visible spectrum, and high photoluminescence quantum yield of up to ≈100%, render metal halide perovskites suitable for next-generation high-definition displays and healthy lighting systems. The external quantum efficiency of perovskite light-emitting diodes (LEDs) increases from 0.1 to 11.7% in three years; however, the energy conversion efficiency and the long-term stability of perovskite LEDs are inadequate for practical application. Strategies to optimize the emitting layer and the device structure, with respect to material design, synthesis, surface passivation, and device optimization, are reviewed and highlighted. The long-term stability of perovskite LEDs is evaluated as well. Meanwhile, several challenges and prospects for future development of perovskite materials and LEDs are identified.

Constructing Mie-Scattering Porous Interface-Fused Perovskite Films to Synergistically Boost Light Harvesting and Carrier Transport

Light harvesting (LH) and carrier transport abilities of a photoactive layer, which are both crucial for optoelectronic devices such as solar cells and photodetectors (PDs), are typically hard to be synergistically improved. Taking perovskite as an example, a freeze-drying recrystallization method is used to construct porous films with improvements of both LH and carrier transport ability. During the freeze-drying casting process, the rapid solvent evaporation produces massive pores, the sizes of which can be adjusted to exploit the Mie scattering for enhancement of the LH ability. Meanwhile, owing to the strong iconicity, the interface between perovskite nanocrystals fused during recrystallization, which favors carrier transport. Subsequently, PDs based on these Mie porous and interface-fused films show a high on/off ratio of more than 104 and an external quantum efficiency value of 658 % under 9 V bias and 520 nm light irradiation.

N- and p-type doping of antimonene

Antimonene, monolayer antimony, was recently predicted to be a two-dimensional (2D) semiconductor with a blue photoresponse. N- and p-type doping of this material is essential for its future application in optoelectronic devices, but has not yet been carried out. Here, we introduce tetrathiafulvalene (TTF) and tetracyanoquinodimethane (TCNQ) as electron and hole dopants to attain n- and p-type antimonene semiconductors. Then, the electronic properties of the chemically doped antimonene are investigated based on comprehensive first-principles calculations. Through TTF modified antimonene, we acquire an n-type semiconductor with a deep donor state of 0.73 eV. Importantly, through TCNQ functionalized antimonene, a p-type semiconductor is achieved with a shallow acceptor state of 0.27 eV. Moreover, the co-adsorption of TTF and TCNQ on antimonene can significantly decrease the band-gaps to 0.15 and 0.12 eV in the one- and two-side configurations, respectively, exhibiting n-type semiconductance with shallow donor states. Such n- and p-type antimonene semiconductors may widen the application of two-dimensional semiconductors in electronics and optoelectronics.

Preparation of superhydrophobic nanodiamond and cubic boron nitride films

Superhydrophobic surfaces were achieved on the hardest and the second hardest materials, diamond and cubic boron nitride (cBN) films. Various surface nanostructures of nanocrystalline diamond (ND) and cBN films were constructed by carrying out bias-assisted reactive ion etching in hydrogen/argon plasmas; and it is shown that surface nanostructuring may enhance dramatically the hydrophobicity of ND and cBN films. Together with surface fluorination, superhydrophobic ND and cBN surfaces with a contact angle greater than 150° and a sliding angle smaller than 10° were demonstrated. The origin of hydrophobicity enhancement is discussed based on the Cassie model.

Boosting Two-Dimensional MoS2/CsPbBr3 Photodetectors via Enhanced Light Absorbance and Interfacial Carrier Separation

Transition metal dichalcogenides (TMDs) are promising candidates for flexible optoelectronic devices because of their special structures and excellent properties, but the low optical absorption of the ultrathin layers greatly limits the generation of photocarriers and restricts the performance. Here, we integrate all-inorganic perovskite CsPbBr3 nanosheets with MoS2 atomic layers and take the advantage of the large absorption coefficient and high quantum efficiency of the perovskites, to achieve excellent performance of the TMD-based photodetectors. Significantly, the interfacial charge transfer from the CsPbBr3 to the MoS2 layer has been evidenced by the observed photoluminescence quenching and shortened decay time of the hybrid MoS2/CsPbBr3. Resultantly, such a hybrid MoS2/CsPbBr3 photodetector exhibits a high photoresponsivity of 4.4 A/W, an external quantum efficiency of 302%, and a detectivity of 2.5 × 1010 Jones because of the high efficient photoexcited carrier separation at the interface of MoS2 and CsPbBr3. The photoresponsivity of this hybrid device presents an improvement of 3 orders of magnitude compared with that of a MoS2 device without CsPbBr3. The response time of the device is also shortened from 65.2 to 0.72 ms after coupling with MoS2 layers. The combination of the all-inorganic perovskite layer with high photon absorption and the carrier transport TMD layer may pave the way for novel high-performance optoelectronic devices.

Recent progress of metal halide perovskite photodetectors

Metal halide perovskites are the rising stars of optoelectric semiconductor materials and have shown great potential in the field of photodetectors, due to their excellent optoelectronic properties such as nearly 100% photoluminescence quantum yields, greater than 175 μm of carrier diffusion length and tunable wavelength of light absorption. In fact, metal halide perovskite based photodetectors covering a broad range of light with sensitive response have been demonstrated. In this review, we focus on the recent progress of metal halide perovskite photodetectors. The synthesis, optoelectronic properties of metal halide perovskites, perovskite photodetectors for different spectral regions, strategies for device performance improvement and applications of photodetectors are reviewed. After summarizing and analyzing the current research and challenges, the outlook is presented for future studies on metal halide perovskite photodetectors.

Structural, electrical and optical properties of Mg-doped CuAlO2 films by pulsed laser deposition

CuAl1−xMgxO2 (x = 0, 0.01, 0.02, 0.05) films were deposited on sapphire and fused silica substrates by pulsed laser deposition and underwent annealing in an Ar atmosphere at the temperature of 1000 °C. The effects of Mg concentration on the structural, morphological, electrical and optical properties were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV-visible-NIR spectrophotometry and a Hall effect measurement system. The results indicate that Mg is successfully doped into the CuAlO2 film with p-type conduction after annealing. Single and pure-phase CuAl1−xMgxO2 (x = 0, 0.01, 0.02, 0.05) films with c-axis orientation are obtained on sapphire substrates in the studied doping range, and a secondary phase is not detected by XRD measurements. The substitution of Mg2+ ions in Al3+ sites induces lattice distortion and results in the decline of the crystalline quality. The Hall effect measurement reveals that the carrier concentration increases and Hall mobility decreases with the increase of Mg doping concentration. The resistivity of the CuAl1−xMgxO2 films decreases and then increases with increasing Mg doping concentration from 0 to 5%. The minimum resistivity of 11.45 Ω cm is obtained at room temperature for the CuAl1−xMgxO2 films with x = 2%. The optical transmittance gradually reduces with the increase of Mg concentration due to the enhancement of absorption of incident photons. The optical band gaps of CuAl1−xMgxO2 films are found to decrease from 3.54 to 3.43 eV as the Mg doping concentration increased from 0 to 5% due to the formation of impurity energy levels.

Amperometric glucose sensor based on boron doped microcrystalline diamond film electrode with different boron doping levels

Boron doped microcrystalline diamond (BDMD) films with different boron concentrations were deposited on Si (100) by microwave plasma chemical vapor deposition in a gas mixture of CH4/H-2/TMB. The influence of boron concentration on the surface morphology, microstructure, and electrochemical properties of BDMD film electrodes was studied. It was found that boron dopants play an important role in the structural quality and electrochemical properties of BDMD film electrodes. The increase of doped boron concentration results in the reduction of diamond grain size and the domination of two peaks located at approximately 500 and 1220 cm(-1) in the Raman spectra. Marked differences are observed for BDMD film electrodes with various boron concentrations in impedance characteristics. The electron transfer reaction on BDMD film electrodes becomes faster and reversibility is improved with the increase of boron concentration. Meanwhile, the electrochemical reactions on the BDMD film electrodes become a diffusion controlled process. The non-enzymatic glucose sensors based on as-prepared BDMD film electrodes were developed. The glucose oxidation peak position and current density are dependent on the B/C ratio for the BDMD film electrodes. The results show that appropriate boron doping concentration can improve the conductivity and electrocatalytic activity of BDMD film electrodes. The BDMD film electrode with B/C ratio of 10 000 ppm exhibits the highest sensitivity of 96.88 mu A mM(-1) cm(-2), lowest detection limit of 0.018 mM and widest linear range of 0.1 to 5 mM. The developed nonenzymatic glucose sensors based on as-prepared BDMD film electrodes demonstrate selective detection of glucose in alkaline solution containing interfering species of ascorbic acid and uric acid.