Zhe Xia

Thermal Evaporation and Characterization of Sb2Se3 Thin Film for Substrate Sb2Se3/CdS Solar Cells

Sb2Se3 is a promising absorber material for photovoltaic cells because of its optimum band gap, strong optical absorption, simple phase and composition, and earth-abundant and nontoxic constituents. However, this material is rarely explored for photovoltaic application. Here we report Sb2Se3 solar cells fabricated from thermal evaporation. The rationale to choose thermal evaporation for Sb2Se3 film deposition was first discussed, followed by detailed characterization of Sb2Se3 film deposited onto FTO with different substrate temperatures. We then studied the optical absorption, photosensitivity, and band position of Sb2Se3 film, and finally a prototype photovoltaic device FTO/Sb2Se3/CdS/ZnO/ZnO:Al/Au was constructed, achieving an encouraging 2.1% solar conversion efficiency.

Effects of temperature and atmosphere on the magnetism properties of Mn-doped ZnO

Magnetic properties of Mn-doped ZnO (Zn0.98Mn0.02O) bulk materials prepared by the solid-state reaction method were investigated by measuring magnetization as functions of temperature and magnetic field. The special feature of our sample preparation was the low-temperature processing. When high-temperature (T>700°C) was used, secondary phase was found. The results indicate that the samples sintered in Ar gas show ferromagnetic behavior at room temperature, but it disappears in samples sintered in air. Even for ferromagnetic samples, the obtained saturation value of magnetization is much smaller than the theoretical value, suggesting the possibility that there is a strong antiferromagnetic exchange coupling in this kind of compound.

Sulfurization induced surface constitution and its correlation to the performance of solution-processed Cu2ZnSn(S,Se)4 solar cells.

To obtain high photovoltaic performances for the emerging copper zinc tin sulfide/selenide (CZTSSe) thin film solar cells, much effort has deservedly been placed on CZTSSe phase purification and CZTSSe grain size enhancement. Another highly crucial but less explored factor for device performance is the elemental constitution of CZTSSe surface, which is at the heart of p-n junction where major photogenerated carriers generate and separate. In this work we demonstrate that, despite the well-built phase and large grained films are observed by common phases and morphology characterization (XRD, Raman and SEM), prominent device efficiency variations from short circuited to 6.4% are obtained. Insight study highlights that the surface (0–250 nm) compositions variation results in different bulk defect depths and doping densities in the depletion zone. We propose that suitable sulfurization (at ~10 kPa sulfur pressure) drives optimization of surface constitution by managing the Cu, Zn and Sn diffusion and surface reaction. Therefore, our study reveals that the balance of elemental diffusion and interface reactions is the key to tuning the surface quality CZTSSe film and thus the performance of as resulted devices.

Electrical transport behavior of La0.67Ca0.33MnO3/Fe3O4 composites

Abstract The influence of Fe 3 O 4 contents on the electrical transport properties (resistivity and ac susceptibility) of a series of composite samples of La 0.67 Ca 0.33 MnO 3 /Fe 3 O 4 is studied. Results show that the Fe 3 O 4 phase not only shifts the intrinsic insulator–metal (I–M) transition temperature T P1 to a lower temperature, but also causes a new I–M transition at a lower temperature T P2 ( T P2 T P1 ). On the basis of an analysis by scanning electron microscopy and X-ray diffraction, we suggest that the decrease of the I–M transition temperature and the formation of the new I–M transition are caused by the segregation of a new phases related to the Fe 3 O 4 at grain boundaries or surfaces of the La 0.67 Ca 0.33 MnO 3 grains.

Characterization of Mg and Fe doped Sb2Se3 thin films for photovoltaic application

Sb2Se3 holds a great potential for low-cost thin film photovoltaics because of its very attractive material and optoelectronic properties, and the demonstrated 5.6% certified efficiency and decent device stability. A full understanding of the influence of external impurities on the properties of Sb2Se3 films would help the further improvement of Sb2Se3 solar cells. In this work, we carefully characterized the Mg and Fe doping in Sb2Se3 films. Both Kelvin probe force microscope and Hall measurements revealed that Mg was largely inert while Fe introduced the n-type doping. Temperature-dependent conductivity and admittance further demonstrated that Fe doping introduced two defect levels within the bandgap with their positions ∼0.3 eV and ∼0.4 eV below the conduction band. We caution that iron contamination should be minimized for high efficiency Sb2Se3 solar cells.

A comparative study of low-field magnetoresistance for La2/3Ca1/3Mn1−xCuxO3 (x = 0% and 4%) synthesized at different temperatures

Polycrystalline samples of nominal La2/3Ca1/3Mn1−xCuxO3 (x = 0% and 4%) were fabricated by a sol–gel method following sintering treatments at temperature Ts ranging between 1000°C and 1300°C. Experiments indicate that doping Cu does not cause a change in crystalline structure, but strongly affects transport and magnetoresistance (MR) properties. For lower Ts, when a low magnetic field of H = 0.3 T, is applied, the x = 0 samples show typical intergrain MR behaviour with a monotonic increase in MR0(≡ Δρ/ρ(H = 0)) on cooling; while for the x = 4% samples, in addition to intergrain MR, a characteristic feature similar to colossal MR (CMR) is observed near the insulator–metal transition. The maximum MR with a value ~80% of that for H = 0.3 T is obtained in the sample prepared at 1100°C, which is comparable to the intrinsic CMR response usually observed in large fields of the order of several teslas.