Showing papers by "Bruno Lucas published in 2018"

Organic thermoelectric devices based on a stable n-type nanocomposite printed on paper

Abstract: We present a fully inkjet-printed flexible thermoelectric device using organic and organic/inorganic hybrid materials. As part of our effort in the development of an n-type material, we present an approach to synthesize a solution processable thermoelectric hybrid material based on in situ oxidative polymerization and intercalation that can yield layered quasi two-dimensional superlattice structures. Thus, we have inserted poly(3,4-ethylenedioxythiophene) (PEDOT) within the nanotemplates of vanadium pentoxide gel (V2O5·nH2O) in order to enhance the charge carrier concentration. Furthermore, for the first time, we adapted the hybrid (PEDOT)xV2O5 material to the inkjet printing technology, thus successfully proving the printability of (PEDOT)xV2O5. Hence, we successfully produced a thermoelectric device composed of 4 thermocouples. Moreover, we optimized the geometry of the organic thermoelectric generator (OTEG) device thanks to a numerical model; the simulated and measured results are presented. The OTEG yielded a power density as high as 0.266 μW cm−2 for a temperature gradient of 20 K, therefore unveiling the potential of hybrid V2O5-based compounds for thermoelectric applications.

Experimental investigation on On-Off current ratio behavior near onset voltage for a pentacene based organic thin film transistor

Abstract: The performance of a pentacene based organic thin film transistor (OTFT) with polymethylmethacrylate as a dielectric insulator and indium tin oxide based electrical gate is investigated. On the one hand, we showed that the threshold voltage increases with gate voltage, and on the other hand that it decreases with drain voltage. Thus, we noticed that the onset voltage shifts toward positive voltage values with the drain voltage increase. In addition, threshold-onset differential voltage (TODV) is proposed as an original approach to estimate an averaged carrier density in pentacene. Indeed, a value of about 4.5 × 10 16 cm −3 is reached at relatively high gate voltage of −50 V; this value is in good agreement with that reported in literature with other technique measurements. However, at a low applied gate voltage, the averaged pentacene carrier density remains two orders of magnitude lower; it is of about 2.8 × 10 14 cm −3 and remains similar to that obtained from space charge limited current approach for low applied bias voltage of about 2.2 × 10 14 cm −3 . Furthermore, high I On / I Off and I On / I Onset current ratios of 5 × 10 6 and 7.5 × 10 7 are reported for lower drain voltage, respectively. The investigated OTFTs also showed good electrical performance including carrier mobility increasing with gate voltage; mobility values of 4.5 × 10 −2 cm 2 V −1 s −1 and of 4.25 × 10 −2 cm 2 V −1 s −1 are reached for linear and saturation regimes, respectively. These results remain enough interesting since current modulation ratio exceeds a value of 10 7 that is a quite important requirement than high mobility for some particular logic gate applications.

Frequency electrical conductivity dependence and dielectric relaxation of ZnO–P 2 O 5 /Co composites

Abstract: This work focuses on the experimental study of the conductivity and the permittivity of ZnO–P2O5/Co (ZP/Co) composites as function of frequency in the range of 100–106 Hz at room temperature. The conductivity evolution shows a high percolating jump from low to high loaded ZP matrix with Co filler, indicating an insulator–semiconductor phase transition. Above the percolation threshold, the obtained conductivity is between 10−1 and 10° S/cm and is frequency independent. While, for low filler volume fraction, it is frequency dependent and it is about 10−8 S/cm at 100 Hz. Moreover, it should be noticed that around the percolation threshold, a significant value of dielectric constant about 105 was observed at room temperature and low frequency 100 Hz. Furthermore, the distribution of the relaxation processes was also investigated below the percolation threshold. Indeed, a relaxation peak about 106 rad/s in the curves of electric modulus M″(ω) was observed. It is successively described by Davidson–Cole model and an account of the interpretation of obtained results is given.

High on-off current modulation ratio investigated at onset voltage for an organic thin film transistor

Abstract: The performance of a pentacene based organic thin film transistor with polymethylmethacrylate as a dielectric insulator and indium tin oxide based electrical gate is investigated. On the one hand, we showed that the threshold voltage increases with gate voltage, and on the other hand that it decreases with drain voltage. Furthermore, high current modulation ratios of 5×106 and 7.5×107 are reported for a lower drain voltage, respectively. These results are very important since current ratio exceeds a value of 107 is a quite interesting requirement than high mobility for some logic gate applications.