Search

The perovskite solar cells (PSCs) are still facing the two main challenges of stability and scalability to meet the requirements for their potential commercialization. Therefore, developing a uniform, efficient, high quality and cost-effective electron transport layer (ETL) thin film to achieve a stable PSC is one of the key factors to address these main issues. Magnetron sputtering deposition has been widely used for its high quality thin film deposition as well as its ability to deposit films uniformly on large area at the industrial scale. In this work, we report on the composition, structural, chemical state, and electronic properties of moderate temperature radio frequency (RF) sputtered SnO2. Ar and O2 are employed as plasma-sputtering and reactive gases, respectively. We demonstrate the possibility to grow a high quality and stable SnO2 thin films with high transport properties by reactive RF magnetron sputtering. Our findings show that PSC devices based on the sputtered SnO2 ETL have reached a power conversion efficiency up to 17.10% and an average operational lifetime over 200 h. These uniform sputtered SnO2 thin films with improved characteristics are promising for large photovoltaic modules and advanced optoelectronic devices. [ABSTRACT FROM AUTHOR]

In the present work, we report on the microstructural and optoelectronic properties of SnOx thin films deposited by a reactive radio frequency magnetron sputtering. After SnOx growth by sputtering under O2/Ar flow, we have used three different treatment methods, namely (1) as deposited films under O2/Ar, (2) vacuum annealed films ex-situ, and (3) air annealed films ex-situ. Effects of the O2/Ar ratios and the growth temperature were investigated for each treatment method. We have thoroughly investigated the structural, optical, electrical and morphology of the different films by several advanced techniques. The best compromise between electrical conductivity and optical transmission for the use of these SnOx films as an n-type TCO was the conditions O2/Ar = 1.5% during the growth process, at 250 °C, followed by a vacuum post thermal annealing performed at 5 × 10–4 Torr. Our results pointed out clear correlations between the growth conditions, the microstructural and optoelectronic properties, where highly electrically conductive films were found to be associated to larger grains size microstructure. Effects of O2/Ar flow and the thermal annealing process were also analysed and discussed thoroughly. [ABSTRACT FROM AUTHOR]

Thin films of Sr2FeMoO6 (SFMO) are grown epitaxially on (001) SrTiO3 substrates by pulsed laser deposition and the effects of the strain relaxation on the electronic properties of SFMO are determined. Ab initio calculations suggest that the variation of SFMO lattice parameters due to strain has a limited impact on the magnetization, and SFMO is half metallic only for thickness above 44 nm.

Exchange coupling is studied in NiO/CoFe(sub 2) and CoFe(sub 2)O(sub 4)/CoFe(sub 2) systems grown by pulsed laser deposition. An exchange coupling of 0.06 and 0.05 erg/cm(super 2) is obtained for NiO/CoFe(sub 2) and CoFe(sub 2)/CoFe(sub 2)O(sub 4) systems, respectively; no coupling is observed when NiO is integrated in the top hard electrode but coupling is observed when a CoFe(sub 2)O(sub 4) layer is used.

Thin films of Sr(sub 2)FeMoO(sub 6)(SFMO) are grown on SrTiO(sub 3) substrates by pulsed laser deposition. The deposition rate is suspected to have a strong influence on the Fe/Mo ordering and highly magnetic samples are obtained under a low gas flow of either 20percent oxygen or a 0.3 percent oxygen or argon.

The lower than expected magnetization of imperfect Sr2FeMoO6 (SFMO) double perovskites is usually attributed to the presence of Fe at antisite positions that would be antiferromagnetically coupled to their regular neighbors. However, ab initio calculations suggest strongly that such defective Fe sites would be ferromagnetically coupled and, consequently, the magnetization reduction would originate from other kinds of defects. The magnetic, hyperfine, and structural properties of SFMO perovskites prepared by solid-state reaction under a variety of conditions are reported and correlated with ab initio calculations of the magnetic moments and hyperfine fields of Mo and Fe ions in different local environments (antisites, antisite neighbors, and neighbors of an oxygen vacancy). When plotted against the order parameter the experimental magnetization is found to decrease at a rate of about -7.6μB per Mo–Fe antisite pair as in other previous experiments, where the theoretical calculation predicts -6.56μB per antisite pair if the moments of Fe antisites are antiparallel to the regular Fe moments. Unfortunately, the energy of this configuration is found to be 0.7 eV higher than that of the parallel configuration for which the magnetization reduction is only -0.19μB per antisite pair. Sources for the supplementary reduction of magnetization have then been considered. The presence of spurious phases cannot account for the observation. Oxygen vacancies do reduce significantly the magnetization (-2.00 μB/vacancy), but no significant sign of their effect is found in the Fe Mössbauer and Mo nuclear magnetic resonance spectra. Moreover, the position of the spectral lines of defects are compatible with the theoretical findings for Fe antisites in the antiparallel spin configuration. [ABSTRACT FROM AUTHOR]

Thin films of Sr2FeMoO6 (SFMO) are grown epitaxially on (001) SrTiO3 substrates by pulsed laser deposition. The in-plane and out-of-plane SFMO lattice parameters are determined for different thicknesses, from 13 to 600 nm. Samples below a critical thickness of around 34 nm are fully strained, samples between 34 and 80 nm are relaxing, and samples between 80 and 600 nm are fully relaxed. Transmission electron microscopy reveals that the relaxation is done by stacking the faults perpendicular to the substrate. Ab initio calculations show first that the variation of SFMO lattice parameters due to strain has a limited impact on the magnetization, which is also observed experimentally. Second, ab initio calculations indicate that SFMO is half metallic only for thicknesses above 44 nm. [ABSTRACT FROM AUTHOR]

Pulsed laser deposition and patterned using optical lithography were used to grow [Sr.sub.2]FeMo[O.sub.6](70nm)/SrTi[O.sub.3](3nm)/Co[Fe.sub.2][O.sub.4](30nm) magnetic tunnel junctions. It was found that the junctions showed no magnetoresistance, but presented a high asymmetry in the current versus voltage curves.

Sr2FeMoO6 (SFMO) double perovskite (DP) in varied conditions is prepared and their magnetic and structural properties with ab initio calculations of the hyperfine fields and local magnetic moments for different types of defects are correlated. The local magnetism is analyzed independently for the Fe and Mo ions, and correlated with the presence of antisite defects.

Sr2FeMoO6(70 nm)/SrTiO3(3 nm)/CoFe2O4(30 nm) magnetic tunnel junctions are grown by pulsed laser deposition and patterned using optical lithography. The square tunnel elements with lateral size of 50 μm exhibit nonlinear zero-field current-voltage (I-V) variation. More interesting, when the temperature is decreased, the I-V curves become highly asymmetric and present a diodelike behavior. In order to explain this behavior, ab initio calculations are performed to obtain the electronic structure for each oxide layer. It is shown that our structure behaves like a usual metal/insulator/semiconductor diode due to the small gap into the majority-spin band of the CoFe2O4 layer. Finally, we point out that the I-V characteristic can be magnetically controlled. [ABSTRACT FROM AUTHOR]

NiO(30 nm)/CoFe2(5 nm) bilayers are grown by pulsed laser deposition on Si (001). After annealing under a magnetic field we observe an exchange bias of -86 Oe, corresponding to an exchange coupling of 0.06 erg/cm2. While a similar exchange coupling is observed in NiO(30 nm)/CoFe2(5 nm)/SrTiO3(3 nm)/Ni80Fe20(5 nm)/Ta(5 nm), the stack SFMO(30 nm)/SrTiO3(3 nm)/CoFe2(5 nm)/NiO(30 nm)/Ta(5 nm) does not provide any exchange bias with NiO on the top electrode. Alternatively, we have used a ferrimagnetic oxide (CoFe2O4) as a bias layer of the top electrode. The stack SFMO(30 nm)/STO(3 nm)/CoFe2(5 nm)/CoFe2O4(70 nm) provides a shift of -70 Oe for the CoFe2(5 nm) layer, corresponding to an exchange coupling of 0.05 erg/cm2. [ABSTRACT FROM AUTHOR]

Thin films of Sr2FeMoO6 (SFMO) are grown on SrTiO3 (001) substrates by pulsed laser deposition. The best films provide 3.2μB/f.u. at 5 K, a Curie temperature above 400 K, low roughness, high crystallinity, and low splashing. Therefore, the use of such SFMO electrodes in magnetic tunnel junctions patterned with conventional lithography is promising. Pseudomorphic epitaxial growth is obtained for thicknesses under 50 nm. Above this thickness the films do not relax homogeneously. A coherent and systematic variation of the magnetization with the deposition conditions is obtained, which highlights a high reproducibility. Under a reasonable O2 partial pressure to avoid parasite phases, the limiting factor for high magnetization is the total pressure or the deposition rate. Therefore, the deposition rate is suspected to have a strong influence on the Fe/Mo ordering. Highly magnetic samples are obtained under a low gas flow of either a 20% O2+N2 or a 0.3% O2+Ar. [ABSTRACT FROM AUTHOR]