Thermal Properties of TiO2/PbS Nanoparticle Solar Cells

Photovoltaic performance is shown to depend on ligand capping on PbS nanoparticle solar cells by varying the temperature between 140K and 350K. The thermal response of open‐circuit voltage, short‐circuit current density, fill‐factor and shunt resistance varies between the ligands. A large increase in short‐circuit current density at low temperatures is observed for 1,2‐ethanedithiol and 3‐mercaptopropionic acid and a relatively constant short-circuit current density is observed for the stiffer 1,4‐benzenedithiol. Dark data provide evidence for tunnelling transport being the dominant charge conduction mechanism for all three ligand devices with recombination occurring within deep trap states. Under illumination, devices exhibit band‐to‐band recombination, indicated by an ideality factor of nearly unity

Effects of Different Surface Functionalization and Doping on the Electronic Transport Properties of M2CTx-M2CO2 Heterojunction Devices

By employing nonequilibrium Green's functions in combination with density functional theory, we have examined the electronic and transport properties of p-type doped, undoped, and n-type doped MXene heterojunctions [M2CTx-M2CO2 (M = Ti, Zr, or Hf; T=F, OH; x = 0 or 2)]. The geometries and electronic band structures are all obtained and the current voltage characteristics are predicted. We found that M2CF2-M2CO2 (M = Ti, Zr) heterojunctions have better electrical conductivity than M2C-M2CO2 and M2C(OH)(2) M2CO2, and Hf2C(OH)(2)-Hf2CO2 shows the best conductivity compared with the cases of other terminations studied herein. Rectification behaviors are observed as important characteristics from some of these devices. Moderate n-type doping is found to be effective in enhancing rectification for Hf2C(OH)(2)-Hf2CO2, and the currents at the intermediate positive bias show an excellent rectification ratio. Moreover, high n-type doping may generate a negative differential resistance (NDR) effect in the Hf2C(OH)(2)-Hf2CO2 heterojunction at a high voltage with a wide bias range, and the high doping concentration of both n- and p-types are found to generate high electrical conductivity. The mechanism of rectification and NDR effects is elaborated in detail from the electronic structure level. These findings not only help us to make appropriate choices in surface groups, doped carrier types, and concentration to improve the performance of MXene heterojunctions, but also provide new insight for guiding the design of novel MXene nanoelectronic devices

The Cooperative Effect of Ag and Cu Co-doping on Morphology and Optical Properties of ZnO Nanorods

Zinc oxide (ZnO) has unique physical and optical properties. Proper doping of ZnO plays an important role in adjusting the photoelectric properties of its optoelectronic devices. In this paper, undoped, Ag-or Cu-doped, and Ag+Cu co-doped ZnO nanorod (NRs) arrays were synthesized by hydrothermal method at low temperature. Meanwhile the influence of doping and co-doping on the morphology, structure, and optical properties of ZnO NRs was investigated. The results show that the ZnO NRs prepared under different doping conditions were of wurtzite structure with strong (002) diffraction peak, and the diffraction peak of Ag+Cu co-doped ZnO NRs was similar to that of undoped ZnO NRs, which was due to the synergistic effect of lattice distortion caused by smaller radius Cu2+ doping and larger radius Ag+ doping than Zn2+. Affected by the size effect of nanorods and the Band Gap Renormalization effect, the UV emission peaks of all doped ZnO NRs had a red shift. Compared with that of undoped ZnO NRs, the intensity of visible emission peak of co-doped ZnO NRs increased slightly owing to the increasing defect concentration such as oxygen vacancy, and lay between that of AZO NRs and CZO NRs. Therefore, the co-doping of Ag and Cu makes it possible for ZnO NRs to be widely used in photoelectric field

Current rectification induced by V-doped and Sc-doped in Ti2CO2 devices

In this work, we have investigated the electron transport properties of MXene devices employing nonequilibrium Green's functions in combination with the density functional theory. Here, the twodimensional (2D) and one-dimensional (1D) devices are built on Ti2CO2 materials, in which one lead is alloyed by V, and the other is by Sc. Ab initio calculations show that there exist rectifying behaviors for both 1D and 2D systems, and the Ti2CO2 nanoribbon devices show stronger rectification ratio than the 2D counterpart. The current results indicate that V-doped and Sc-doped electrodes may be a practical way to achieve the current rectification of MXene devices. Finally, the I-V curves for 2D Ti2CO2 under different gate voltage are studied as well. According to data, the currents in a doped Ti2CO2-based device are found to be controllable under the dual-gate induced electric field. (C) 2017 Elsevier B.V. All rights reserved