Layered V 2 O 5 hydrate has been applied as the hole transport layer (HTL) in organic solar cells (OSCs). V 2 O 5 is obtained from a sodium metavanadate solution in water under ambient conditions, resulting in a final thin film of formula V 2 O 5 $0.5H 2 O. The 0.5 water molecules are not removed from the V 2 O 5 layered structure unless the sample is heated above 250 C, which makes the thin film highly stable under real working conditions. The HTL was used in OSCs in the normal and the inverted configurations, applying metallic Ag as the back-metal electrode in both cases. Fabrication of both OSC configurations completely by solution-processing printing methods in air is possible, since the Al electrode needed for the normalconfiguration OSC is not required. The work function (WF) and band gap energy (BG) of the V 2 O 5 thin films were assessed by XPS, UPS and optical analyses. Different WF values were observed for V 2 O 5 prepared from a fresh V 2 O 5-isopropanol (IPA) solution (5.15 eV) and that prepared from a 24 hold solution (5.5 eV). This difference is due to the gradual reduction of vanadium (from V 5+ to V 4+) in IPA. The OSCs made with the V 2 O 5 thin film obtained from the 24 hold V 2 O 5-IPA solution required photoactivation, whereas those made with the freshly obtained V 2 O 5 did not. Outdoor stability analyses of sealed OSCs containing a V 2 O 5 HTL in either configuration revealed high stability for both devices: the photovoltaic response at T 80 was retained for more than 1000 h. Broader context Organic Solar Cells (OSCs) have achieved an impressive increase in power conversion efficiency in the past few years, with values above the 12% range. Yet, in order to be competitive with existing energy sources from fossil fuels and modern inorganic photovoltaic technologies, OSCs must reduce fabrication costs and improve its energy payback time (EPBT). To achieve the latter, the fabrication of OSCs by large scale, solution processing methods applying inexpensive, low temperature techniques is required. An important aim is the exclusion of toxic organic solvents, being water-based or alcohol-based solutions is highly desired. In this work, a layered V 2 O 5 hydrate has been applied as the hole transport layer in stable OSCs. V 2 O 5 is obtained from the dissolution of sodium metavanadate in water under ambient atmospheric conditions, resulting in a nal thin lm with the V 2 O 5 $0.5H 2 O formula. OSCs with normal and inverted conguration applying metallic Ag as the back metal electrode in both cases have been fabricated. The use of a Ag electrode eliminates the need for a highly reactive work function metal electrodes (Al, Ca) for the normal conguration OSC, and permits the fabrication of both OSC congurations completely by solution processing printing methods in air. Outdoor stability analyses of sealed devices showed high stability, maintaining the photovoltaic response at T 80 for more than 1000 h.

In this work, we report magnetoelectric coefficient measurements in BiFeO3 (BFO) compounds using dynamic lock-in technique to evidence magnetoelectric coupling behavior. The response of the magnetoelectric coefficient shows rapid increase from low frequencies (0.1kHz) to around 5kHz, reaching a maximum, and then decreasing monotonously to 100kHz. For a constant frequency at 7kHz, the maximum magnetoelectric coefficient was close to 7mV∕cmOe, obtained at a bias magnetic field of H=120Oe. Thus, we demonstrated the feasibility of this technique for characterizing multiferroic materials.

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Three-dimensional magnetophotonic crystals (3D-MPCs) are being postulated as appropriate platforms to tailor the magneto-optical spectral response of magnetic materials and to incorporate this functionality in a new generation of optical devices. By infiltrating self-assembled inverse opal structures with monodisperse nickel nanoparticles we have fabricated 3D-MPCs that show a sizable enhancement of the magneto-optical signal at frequencies around the stop-band edges of the photonic crystals. We have established a proper methodology to disentangle the intrinsic magneto-optical spectra from the nonmagnetic optical activity of the 3D-MPCs. The results of the optical and magneto-optical characterization are consistent with a homogeneous magnetic infiltration of the opal structure that gives rise to both a red-shift of the optical bandgap and a modification of the magneto-optical spectral response due to photonic bandgap effects. The results of our investigation demonstrate the potential of 3D-MPCs fabricated following the approach outlined here and offer opportunities to adapt the magneto-optical spectral response at optical frequencies by appropriate design of the opal structure or magnetic field strength.

Coupling magnetic materials to plasmonic structures provides a pathway to dramatically increase the magneto-optical response of the resulting composite architecture. Although such optical enhancement has been demonstrated in a variety of systems, some basic aspects are scarcely known. In particular, reflectance/transmission modulations and electromagnetic field intensification, both triggered by plasmon excitations, can contribute to the magneto-optical enhancement. However, a quantitative evaluation of the impact of both factors on the magneto-optical response is lacking. To address this issue, we have measured magneto-optical Kerr spectra on corrugated gold/dielectric interfaces with magnetic (nickel and iron oxide) nanoparticles. We find that the magneto-optical activity is enhanced by up to an order of magnitude for wavelengths that are correlated to the excitation of propagating or localized surface plasmons. Our work sheds light on the fundamental principles for the observed optical response and demonstrates that the outstanding magneto-optical performance is originated by the increase of the polarization conversion efficiency, whereas the contribution of reflectance modulations is negligible.

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Material selective sensitivity of a magneto-optical polar Kerr effect to magnetic contributions from different inclusions in self-organized magnetic nanostructures is presented. The method is supported by modeling of the magneto-optic response based on the effective medium approximation and by hysteresis loop measurement of the multiferroic BiFeO3–CoFe2O4 self-assembled nanostructure. Magneto-optic selective sensitivity is demonstrated and explained as an effect of different complex diagonal and off-diagonal permittivity tensor elements of two materials.