An easily prepared Ag8GeS6 nanocrystal and its role on the performance enhancement of polymer solar cells

Novel Ag₈GeS₆ nanocrystal materials (AGS NCs) have recently earned affectionate attention due to its bulk band-gap of 1.4 eV, which makes it ideal as a broad-spectrum absorber material for both semiconductor photocatalyst and photovoltaic devices. In this paper, we investigated the role of AGS NCs as molecular dopant on solution-processed polymer solar cells (PSCs). Argyrodite AGS NCs was prepared via a colloidal synthesis process using simple inorganic compounds as precursors. Incorporating AGS NCs into PSCs leads to not only improved light absorption of active layer but also increased phase separation of donor and acceptor. Moreover, the doping effect of AGS NCs was also confirmed by nanoscale morphology and photocurrent generation mechanism analysis, revealing that AGS NCs could serve as both exciton dissociation centers and charge transfer medium. This study shows that employment of AGS NCs is a facile way to improve the electrical and optical properties of organic photovoltaic devices.     

Realizing efficient exciton dissociation in an all-organic heterojunction photocatalyst for highly improved photocatalytic H2 evolution

Although graphitic carbon nitride is a promising photocatalyst in the field of energy conversion and environmental purification, the intrinsic properties like excitonic effects and sluggish charge transfer restrict further photocatalytic applications. To circumvent these limitations, the novel all-organic heterojunction photocatalysts were constructed by anchoring organic carbon dots (O-dots) on porous graphitic carbon nitride nanosheets (O-dots/CNS). Results demonstrated that excitons can be e?ectively dissociated into electrons and holes at the interface of O-dots/CNS heterojunction, followed by holes injected to O-dots and electrons accumulated in CNS to realize efficient charge separation. Consequently, the O-dots/CNS with the optimized hydrogen (H₂) evolution performance could be reached 1564.5 μmol h^?1g^?1 under the visible light irradiation. This work not only presents new ideas for rational design photocatalytic reaction system from exciton and charge carrier, but also broaden the applications of this new kind of organic dots in the field of energy conversion.     

Bright electroluminescence from single-layer organic light-emitting diodes comprising an ambipolar carrier transport layer of phenyldipyrenylphosphine oxide

We investigated the carrier transport and recombination characteristics of single-layer organic light-emitting diodes (SLOLEDs) composed of a phenyldipyrenylphosphine oxide (POPy₂) layer doped with orange fluorescent molecules of 2,5-bis-[{bis-(4-methoxy-phenyl)-amino}-styryl]-terephthalonitrile (BST). The SLOLEDs achieved a high external quantum efficiency of 1.6% and a high luminance of 24,000 cd/m² at a low driving voltage of 8 V. These very good electroluminescence characteristics originate from factors that include our use of the following: (1) the ambipolar POPy₂ layer, which can transport balanced amounts of electrons and holes, (2) a high BST-doping concentration that traps injected carriers on BST molecules, and (3) insertion of an undoped POPy₂ layer next to a metallic cathode to prevent exciton quenching.     

Investigation on the synthesis and quantum confinement effects of pure and Mn added Zn(1−x)CdxS nanocrystals

Zn_(1−x)Cd_xS and Zn_(1−x)Cd_xS:Mn²⁺ semiconductor quantum dots (2-4 nm) have been prepared by a novel solvothermal route assisted microwave heating method. The growth parameters governing the smaller size and higher yield have been optimized. The synthesized QDs exhibit a significant blue shift as compared to their corresponding bulk counterpart in the UV-vis optical absorption spectrum. The dielectric constant value varies from 2.79 to 6.17 (at 40 °C, 1 kHz) depending upon the composition of the alloy; lower value corresponds to Zn_0.75Cd_0.25S:Mn²⁺ and the higher value corresponds to Zn_0.25Cd_0.75S:Mn²⁺. The crystallite size to exciton bohr radius ratio being <1 indicates a strong quantum confinement effect in both CdS and ZnS QDs. The quantum confinement effect exists in the sequence of ZnS:Mn²⁺ < Zn_(1−x)Cd_xS:Mn²⁺ (x < 0.5) < ZnS < Zn_(1−x)Cd_xS < CdS < CdS:Mn²⁺.     

Exciton quantum confinement in nanocones formed on a surface of CdZnTe solid solution by laser radiation

The investigation of surface morphology using atomic force microscope has shown self-organizing of the nanocones on the surface of CdZnTe crystal after irradiation by strongly absorbed Nd:YAG laser irradiation at an intensity of 12.0 MW/cm². The formation of nanocones is explained by the presence of a thermogradient effect in the semiconductor. The appearance of a new exciton band has been observed after irradiation by the laser which is explained by the exciton quantum confinement effect in nanocones.     

Advances in Materials Research for Displays from Serendipity to Materials by Design

New materials have been developed for PDP for fast addressing and power reduction.They show the transition in R&D from materials invented accidentally to materials-by-design.Cathode-luminescence on MgO...     

Research progress on g–C3N4–based photocatalysts for organic pollutants degradation in wastewater: From exciton and carrier perspectives

Graphitic carbon nitride (g-C₃N₄) can be used to degrade organic pollutants in wastewater owing to its excellent chemical stability, tunable band structure, and visible light (VL) responsiveness. Nevertheless, the application of pristine g-C₃N₄ is significantly hindered by its low specific surface area, unsatisfactory VL utilization (<460 nm), high exciton binding energy (E_b ≈ 0.2 eV), and low photoinduced carrier separation. Development of strategies to overcome these limitations and improve the degradation efficiency has attracted considerable attention. Considering the principles of photoexcitation, this paper describes two unique photoexcitation processes, the carrier and exciton processes, of which the strong exciton effect of g-C₃N₄ has not been extensively discussed in prior reviews. In addition, we comparatively present the latest progress and related mechanisms of the modification strategies such as morphology controlling, elemental doping, defect engineering, and heterojunction building employed in polluted water treatment are compared from the carrier and exciton perspectives. Finally, the unique characteristics, challenges, and future directions are discussed. This review presents research progress on the photoexcitation processes involved in g–C₃N₄–based materials, and proposes that the modification based on the exciton effect and direct verification of the transfer mechanism in the heterojunction can be potential areas of future investigations.     

Enabling high dielectric response and low electrical leakage in polymer/mesoporous-silica@CdTe-quantum-dots nanocomposites by excitonic dipoles and pore-canal restriction

High dielectric response and low leakage conduction are desired in polymer/ceramic composite dielectrics for capacitive energy storage. Rational structural design of hybrid ceramic filler can lead to a balance between high dielectric constant and insulation in composites. In this study, high dielectric constant and breakdown strength were achieved in fluoropolymer/mesoporous silica@CdTe nanocomposite films. Mesoporous silica nanoparticles (MSNs) were employed owing to their high insulation and complex electron-leakage channel. CdTe quantum dots combined with pore-canal inwalls of MSNs were employed because of their internal exciton polarization and MSNs/CdTe interface polarization. Compared with polymer/MSNs composites, polymer/MSNs@CdTe composites exhibited remarkably improved dielectric constant, slightly increased dielectric loss, and slightly reduced breakdown strength. High dielectric constant of ternary composites was ascribed to exciton orientation inside CdTe and interfacial dipole orientation between MSNs and CdTe. High breakdown strength was attributed to high insulation in MSNs and long-range electron transfer inside MSNs@CdTe. An optimal ternary composite with 12 wt% MSNs@CdTe showed a high dielectric constant of ~56, low dielectric loss of ~0.19 at 100 Hz, and high breakdown strength of ~308 MV m^-1. The results of this study can provide insights for enabling large-scale fabrication of modern composite dielectrics based on mesoporous particles@semi-conductive quantum dots fillers.     

Photoluminescence studies of CdS thin films annealed in CdCl2 atmosphere

We have grown CdS films by the Close Spaced Vapor Transport technique under specific conditions: substrate temperature (T_s): 450 °C, source temperature (T_so): 725 °C, argon pressure in the chamber (P_Ar): 100, 200 and 500 mT, deposition time (t_d): 100 s. The films were studied by measuring the luminescence properties at different temperatures in the range 10–300 K. The room-temperature PL spectrum of the as-grown CdS films showed a very broad band centered at 2.26 eV and a shoulder in the low-energy side at 1.80 eV. After CdCl₂ thermal annealing at 300 K, the spectrum showed better PL characteristics: a strong band in the low-energy side at 1.67 eV and a band in the high-energy side at 2.47 eV. The analysis at lower temperatures showed that the high-energy band becomes most intense and shifts to higher energies reaching a value of 2.54 eV, very close to the energy band gap at 10 K. The low-energy band becomes broader and centered around 1.9 eV. Analysis of the PL intensity as a function of temperature in an Arrhenius representation, allows applying a theoretical model for the quenching of the PL intensity.