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Hybrid organic–inorganic perovskites have generated considerable research interest in the field of optoelectronic devices. However, there have been significantly fewer reports of their thermoelectric properties despite some promising early results. In this article, we investigate the thermoelectric properties of bismuth-doped CH3NH3PbBr3 (MAPbBr3) single crystals. The high-quality Bi-doped crystals were synthesized by inverse temperature crystallization and it was found that Bi substitutes onto the B-site of the ABX3 perovskite lattice of MAPbBr3 crystals with very little distortion of the crystal structure. Bi doping does not significantly alter the thermal conductivity but dramatically enhances the electrical conductivity of MAPbBr3, increasing the charge carrier density by more than three orders of magnitude. We obtained a negative Seebeck coefficient of −378 μV K−1 for 15% (x = 0.15) Bi-doped MAPb(1−x)BixBr3 confirming n-type doping and also measured the figure of merit, ZT. This work highlights routes towards controlled substitutional doping of halide perovskites to optimise them for thermoelectric applications.

This research concerns the effect of conductive network formation in a polymer melt on the conductivity of multi-walled carbon nanotube/thermoplastic polyurethane composite systems. An extremely low percolation threshold of 0.13 wt.% was achieved in hot-pressed composite film samples, whereas a much higher CNT concentration (3-4 wt.%) is needed to form a conductive network in extruded composite strands. This is explained in terms of the dynamic percolation behaviour of the CNT network in the polymer melt. The temperature and CNT concentration needed for dynamic percolation to take effect were studied by the conductivity versus temperature behaviour of extruded strands, in an attempt to optimise the processing conditions. © 2008 Elsevier Ltd. All rights reserved.

Field emission properties of B-doped carbon nanotubes are investigated from both theoretical and experimental standpoints. Using tight-binding and ab initio calculations, it is observed that B-saturating tip edges of carbon nanotubes induce the presence of large peaks within the local density of states (LDOS) located in an energy region close to the Fermi level (Ef). These localized states suggest a field emission enhancement for the B-doped tubes. In addition, ab initio theoretical results indicate that the work function for B-doped tubes is 1.7 eV lower when compared to pure carbon-terminated nanotubes. Experimentally, it is found that B-doped tubes, which are produced by arc discharge techniques and contain B mainly at the tips, exhibit stable electron field emission at lower turn-on voltages (1.4 V/mum) when compared to pure single- and multiwalled carbon nanotubes (2.8 and 3.0 V/mum, respectively) measured under the same conditions. We strongly believe our results will bring new insights in the fabrication of stable field emission sources.