Room temperature dielectric bistability in solution-processed spin crossover polymer thin films
Journal of Materials Chemistry C Royal Society of Chemistry 4 (2016) 6240-6248
Abstract:
The spin crossover (SCO) phenomena are a remarkable example of state spin switching at the molecular level. The low- and high-spin states can be reversibly selected through application of external stimulus - often simply a variation in temperature. Since the particular spin-state embodies optical, electronic and structural characteristics, the spin switching can be readily detected or probed using a variety of techniques. In this regard, SCO phenomena show great promise for a range of devices. The key to this uptake is the preparation of high-quality, thin-films capable of retaining SCO properties, and solution-based materials, in particular, provide further opportunities for integration or blending with other functional materials. The present work examines SCO behaviour from two iron(II)-triazole polymers, with short and long side chains, prepared and examined in a variety of formats – from bulk powders to thick and thin films. Magnetic, optical and electronic techniques all verify the SCO behaviour is faithfully maintained for all formats. The two materials serve to highlight the impact on key properties arising from the different density of Fe atoms. The results, all from solution-based materials, are extremely promising and clearly emphasise the growing capability of materials and processing advances associated with SCO materials.Nanoscale current spreading analysis in solution-processed graphene oxide/silver nanowire transparent electrodes via conductive atomic force microscopy
Journal of Applied Physics American Institute of Physics 119:19 (2016) 195501-195501
Charge-Carrier Density Independent Mobility in Amorphous Fluorene-Triarylamine Copolymers
Advanced Functional Materials Wiley (2016)
Abstract:
A charge-carrier density dependent mobility has been predicted for amorphous, glassy energetically disordered semiconducting polymers, which would have considerable impact on their performance in devices. However, previous observations of a density dependent mobility are complicated by the polycrystalline materials studied. Here charge transport in field-effect transistors and diodes of two amorphous, glassy fluorene-triarylamine copolymers is investigated, and the results explored in terms of a charge-carrier density dependent mobility model. The nondispersive nature of the time-of-flight (TOF) transients and analysis of dark injection transient results and transistor transfer characteristics indicate a charge-carrier density independent mobility in both the low-density diode and the high-density transistor regimes. The mobility values for optimized transistors are in good agreement with the TOF values at the same field, and both have the same temperature dependency. The measured transistor mobility falls two to three orders of magnitude below that predicted from the charge-carrier density dependent model, and does not follow the expected power-law relationship. The experimental results for these two amorphous polymers are therefore consistent with a charge-carrier density independent mobility, and this is discussed in terms of polaron-dominated hopping and interchain correlated disorder.Significant Stability Enhancement in High-Efficiency Polymer:Fullerene Bulk Heterojunction Solar Cells by Blocking Ultraviolet Photons from Solar Light.
Advanced science (Weinheim, Baden-Wurttemberg, Germany) 3:4 (2016) 1500269
Abstract:
Achievement of extremely high stability for inverted-type polymer:fullerene solar cells is reported, which have bulk heterojunction (BHJ) layers consisting of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene-alt-3-fluorothieno[3,4-b]thiophene-2-carboxylate] (PTB7-Th) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM), by employing UV-cut filter (UCF) that is mounted on the front of glass substrates. The UCF can block most of UV photons below 403 nm at the expense of ≈20% reduction in the total intensity of solar light. Results show that the PTB7-Th:PC71BM solar cell with UCF exhibits extremely slow decay in power conversion efficiency (PCE) but a rapidly decayed PCE is measured for the device without UCF. The poor device stability without UCF is ascribed to the oxidative degradation of constituent materials in the BHJ layers, which give rise to the formation of PC71BM aggregates, as measured with high resolution and scanning transmission electron microscopy and X-ray photoelectron spectroscopy. The device stability cannot be improved by simply inserting poly(ethylene imine) (PEI) interfacial layer without UCF, whereas the lifetime of the PEI-inserted PTB7-Th:PC71BM solar cells is significantly enhanced when UCF is attached.Long‐range proton conduction across free‐standing serum albumin mats
Advanced Materials Wiley‐VCH Verlag 28:14 (2016) 2692-2698