Synthesis and characterization of Ag2S x Se1-x nanocrystals and their photoelectrochemical property.

I-VI chalcogenide low-toxicity semiconductors and their near-infrared optical property are of great importance for solar cell and biological probe applications. Here, we report the synthesis of Ag2S x Se1-x (x = 0-1) ternary nanocrystals (NCs) and their photoelectrochemical properties, using a refined simple hot-injection reaction recipe. The ICP-MS results show the change of non-metallic composition in products and precursors, which can be well fitted with Vegard's equation. Ternary alloying broadens the absorption spectrum region of Ag2S NCs. It can also balance the transfer of photo-excited electrons through the interfaces of TiO2/Ag2S x Se1-x and Ag2S x Se1-x /electrolyte by minimizing electron-hole recombination. By tuning the compositions, an increase in power conversion efficiency (PCE) was observed with the increase of S composition and the size of the NCs. The photoelectrochemical results reveal that Ag2S x Se1-x ternary NCs exhibit higher conversion efficiency than pure binary NCs. The drop in PCE of the binary NCs is mainly attributed to the decreases of the charge separation following exciton transition.

Colloidal PbSe Solar Cells with Molybdenum Oxide Modified Graphene Anodes.

With good electrical conductivity, optical transparency, and mechanical compliance, graphene films have shown great potential in application for photovoltaic devices as electrodes. However, photovoltaic devices employing graphene anodes usually suffer from poor hole collection efficiency because of the mismatch of energy levels between the anode and light-harvesting layers. Here, a simple solution treatment and a low-cost solution-processed molybdenum oxide (MoOx) film were used to modify the work function of graphene and the interfacial morphology, respectively, yielding highly efficient hole transfer. As a result, the graphene/MoOx anodes demonstrated low surface roughness and high electrical conductivity. Using the graphene/MoOx anodes in PbSe nanocrystal solar cells, we achieved 1 sun power conversion efficiency of 3.56%. Compared to the control devices with indium tin oxide anodes, the graphene/MoOx-based devices show excellent performance, demonstrating the great potential of the graphene/MoOx anodes for use in optoelectronics.

Single layer graphene electrodes for quantum dot-light emitting diodes.

Single layer graphene was employed as the electrode in quantum dot-light emitting diodes (QD-LEDs) to replace indium tin oxide (ITO). The graphene layer demonstrated low surface roughness, good hole injection ability, and proper work function matching with the poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) layer. Together with the hole transport layer and electron transport layer, the fabricated QD-LED showed good current efficiency and power efficiency, which were even higher than an ITO-based similar device under low current density. The result indicates that graphene can be used as anodes to replace ITO in QD-LEDs.

Planar temperature sensing using heavy-metal-free quantum dots with micrometer resolution.

This work describes a micrometer resolution and plane-array temperature-sensing method using the photoluminescence (PL) of ZnCuInS/ZnSe/ZnS quantum dots (QDs). Heavy-metal-free QDs were directly deposited on a printed circuit board to analyze the surface temperature of the devices on the board. An optical fiber monochromator and a high-powered microscope were employed to fabricate a system which could collect temperature-dependent QD emissions from the micrometer area for the temperature measurements. This system realizes the imaging of the surface temperature distribution in the planar micrometer area. Temperature sensitivity of the PL intensity reached 0.66% °C(-1), and the relative error was less than 2%.

Electronic properties of four typical zigzag-edged graphyne nanoribbons.

The subband structures and edge magnetism of α-, ß-, γ- and (6, 6, 12)-graphyne nanoribbons with zigzag edges are studied by means of ab initio calculations. Dispersionless subbands and antiparallel edge magnetic ordering occur in these nanostructures, just like in zigzag-edged graphene nanoribbons. More importantly, a very simple tight-binding model is established which can accurately describe the subband structures of these ribbons. From such a model we find that ß-graphyne nanoribbon has many more transport modes than other graphyne and graphene nanoribbons, hence it can carry a much larger current. Such a tight-binding model provides a simple but effective way to study further the transport and optical properties of these graphyne nanoribbons.

RKKY interaction in AB-stacked multilayer graphene.

The RKKY interaction between two magnetic impurities absorbed on the surface layer of half-filled AB-stacked multilayer graphene (ABSMLG) is theoretically studied based on the lattice Green's function technique. In comparison with the case of monolayer graphene, the RKKY interaction in such multilayer graphene presents distinct properties in some aspects. Firstly, from the numerical results, we find that the thickness of the ABSMLG influences the RKKY interaction in a complicated manner, depending on the odd/even parity of the number of layers and the sublattice attribution of the positions of the two magnetic impurities. Then, we derive the asymptotic expressions of the RKKY interactions in ABSMLG in the long-distance limit. For even-layered ABSMLG, we find that the RKKY interactions of the 1A-1A, 1B-1A and 1B-1B couplings fall off as 1/R(2), 1/R(4) and 1/R(6) (1A and 1B stand for, respectively, the sublattice points in the surface layer, which are positioned directly on the plaquette and on a lattice point of the layer underneath). On the other hand, in odd-layered ABSMLG, the decays of these interactions follow the 1/R(2), 1/R(3) and 1/R(3) power laws respectively. In addition, we also find that these analytical expressions are quantitatively valid to describe the RKKY interaction in ABSMLG when the distance between the two magnetic impurities is larger than the lattice constant of graphene by one order of magnitude.