Unraveling the Characteristic Shape for Magnetic Field Effects in Polymer–Fullerene Solar Cells

Spin-dependent effects in organic solar cells (OSCs) are responsible for tuning the electric current when an external magnetic field is applied. Here, we report the magnetic field effect (MFE) on wide-bandgap (WBG) solar cells based on the polymers PBDT­(O)-T1 and PBDT­(Se)-T1 blended with PC₇₀BM. Furthermore, we propose an experimental method based on the electrical transport (<i>i</i>–<i>V</i>) measurements to unveil the negative magneto conductance (MC) at small bias. The observed curves in a double-logarithmic scale display a particular S-like shape, independent of the OSC power conversion efficiency (PCE) or MC amplitudes. Additionally, from the slope of the S-like shape curve, it is possible to identify the fullerene concentrations that would result in the minimum MC and the maximum PCE. Our work opens up a door to find more patterns to describe MFE and PCE in polymer–fullerene solar cells, without the application of external magnetic or luminous sources

Structural and Magnetic Properties of LaCoO₃/SrTiO₃ Multilayers

Structural and magnetic properties of the LaCoO₃/SrTiO₃ (LCO/STO) multilayers (MLs) with a fixed STO layer of 4 nm but varied LCO layer thicknesses have been systematically studied. The MLs grown on Sr_0.7La_0.3Al_0.65Ta_0.35O₃ (LSAT) and SrTiO₃ (STO) exhibit the in-plane lattice constant of the substrates, but those on LaAlO₃ (LAO) show the in-plane lattice constant between those of the first two kinds of MLs. Compared with the LCO single layer (SL), the magnetic order of the MLs is significantly enhanced, as demonstrated by a very slow decrease, which is fast for the SL, of the Curie temperature and the saturation magnetization as the LCO layer thickness decreases. For example, clear ferromagnetic order is observed in the ML with the LCO layer of ∼1.5 nm, whereas it vanishes below ∼6 nm for the LCO SL. This result is consistent with the observation that the dark stripes, which are believed to be closely related to the magnetic order, remain clear in the MLs while they are vague in the corresponding LCO SL. The present work suggests a novel route to tune the magnetism of perovskite oxide films