Synergistically Improved Thermoelectric Energy Harvesting of Edge-Oxidized-Graphene-Bridged N-Type Bismuth Telluride Thick Films.

Power generation through the thermoelectric (TE) effect in small-sized devices requires a submillimeter-thick film that is beneficial to effectively maintain ΔT compared with a micron-scale thin film. However, most TE thick films, which are fabricated using printing technologies, suffer from low electrical conductivity due to the porous structures formed after sintering of the organic binder-mixed TE ink. In this study, we report an n-type TE thick film fabricated through bar-coating of the edge-oxidized-graphene (EOG)-dispersed Bi2.0Te2.7Se0.3 (BTS) paste with copper dopants. We have found that EOG provides the conducting pathway for carriers through electrical bridging between the separated BTS grains in porous TE thick films. The simultaneous enhancement in electrical conductivity and the Seebeck coefficient of the EOG-bridged TE film result in a maximum power factor of 1.54 mW·m-1·K-2 with the addition of 0.01 wt % EOG. Furthermore, the single element made of an n-type EOG-bridged BTS exhibits a superior output power of 1.65 µW at ΔT = 80 K. These values are 5 times higher than those of bare BTS films. Our results clearly indicate that the utilization of EOG with a metal dopant exerts a synergistic effect for enhancing the electrical output performance of n-type TE thick films for thermal energy harvesters.

Piezoelectric Energy Harvesting from Two-Dimensional Boron Nitride Nanoflakes.

Two-dimensional (2D) piezoelectric hexagonal boron nitride nanoflakes (h-BN NFs) were synthesized by a mechanochemical exfoliation process and transferred onto an electrode line-patterned plastic substrate to characterize the energy harvesting ability of individual NFs by external stress. A single BN NF produced alternate piezoelectric output sources of ∼50 mV and ∼30 pA when deformed by mechanical bendings. The piezoelectric voltage coefficient (g11) of a single BN NF was experimentally determined to be 2.35 × 10-3 V·m·N-1. The piezoelectric composite composed of BN NFs and an elastomer was spin-coated onto a bulk Si substrate and then transferred onto the electrode-coated plastic substrates to fabricate a BN NFs-based flexible piezoelectric energy harvester (f-PEH) which converted a piezoelectric voltage of ∼9 V, a current of ∼200 nA, and an effective output power of ∼0.3 µW. This result provides a new strategy for precisely characterizing the energy generation ability of piezoelectric nanostructures and for demonstrating f-PEH based on 2D piezomaterials.