KAUST Workshop Organic Semiconductors and Flexible Electronics
Molecular dopants regulate structural disorder of DPP-based conjugated polymer toward high-performance n-type organic thermoelectrics.(2022-10-09) [Poster]Molecular doping has become the dominating strategy to optimize the performance of organic thermoelectrics (OTEs). While effective, this method remains largely limited by the inverse relationship between the components of the thermoelectric figure of merit, namely the electrical conductivity (?) and the Seebeck coefficient (?). Increasing the charge carrier density via molecular doping is beneficial for ? but detrimental for ?. Novel n-type conjugated polymers display improved ? since their chemical structure allows enhanced doping efficiencies however, this often leads to a quick decrease in ?. In this work, we demonstrate that careful selection of a host-dopant system leads to reduced structural disorder and increased anisotropy, resulting in high ? with minimal reduction of ?. We blend the n-type conjugated polymer 2DPP-2CNTVT with three state-of-the-art n-type dopants: TBAF, N-DMBI, and TAM. TBAF and TAM show conventional trends i.e., only high ? or only high ? respectively. On the other hand, N-DMBI shows high values for both parameters achieving an n-type power factor of 99.3 ?Wm-1K-1. GIXRD assessment demonstrates that N-DMBI doping increases the film crystallinity and changes the original bimodal orientation to a preferential edge-on orientation. This remarks the importance of host-dopant matching and provides a roadmap to decouple the ?-? inverse relationship toward realizing high-performance OTEs.
Comprehensive model for the thermoelectric properties of 2D carbon nanotube networks(2022-10-09) [Poster]Networks of semiconducting single-walled carbon nanotubes (SWCNTs) are interesting thermoelectric materials due to the interplay between CNT and network properties. Here we present a unified model to explain the charge and energy transport in SWCNT networks. We used the steady-state master equation for the random resistor network containing both the intra- and inter-tube resistances, as defined through their 1D density of states that is modulated by static Gaussian disorder. The tube resistance dependence on the carrier density and disorder is described through the Landauer formalism. Electrical and thermoelectric properties of the network were obtained by solving Kirchhoff s laws through a modified nodal analysis, where we used the Boltzmann transport formalism to obtain the conductivity, Seebeck coefficient, and electronic contribution to the thermal conductivity. The model provides a consistent description of a wide range of previously published experimental data for temperature and charge carrier density-dependent conductivities and Seebeck coefficients, with energetic disorder being the main factor to explain the experimentally observed mobility upswing with carrier concentration. Moreover, we show that for lower disorder energies, the Lorentz factor obtained from the simulation is in accordance with the Wiedemann-Franz law for degenerate band semiconductors. At higher disorder, deviations from simple band behavior are found. Suppressed disorder energy and lattice thermal conductivity can be a key to higher thermoelectric figures of merit in SWCNT networks, possibly approaching or even exceeding zT=1. The general understanding of the transport phenomena will help the selection of chirality, composition and charge carrier density of SWCNT networks to improve their efficiency of thermoelectric energy conversion.
The Role of Oxygen in the Operation of Organic Enzymatic Metabolite Sensors(2022-10-09) [Poster]When combined with oxidase enzymes, the NDI-T2 based electron transporting (n-type) polymer led to high performance metabolite sensors, yet their working mechanism has been poorly understood.1,2 By monitoring oxygen, hydrogen peroxide, and pH changes in the electrolyte surrounding the n-type channel and gate as well as the potential of each electrical contact in the transistor, we shed light on the catalytic events occurring at the polymer-enzyme interface. We show that in its doped sate, the n-type film performs oxygen reduction reaction and that the n-OECT characteristics are sensitive to oxygen. We find a correlation between the amount of dissolved oxygen and the n-OECT sensor current generated during the metabolite oxidation and that using the n-type polymer at the gate electrode is critical for sensor operation. Our results show the importance of in operando analysis for understanding polymer-catalytic enzyme activity, as well as the importance of ambient oxygen in the operation of n-type devices. 1: Pappa, A. M.; Ohayon, D.; Giovannitti, A.; Maria, I. P.; Savva, A.; Uguz, I.; Rivnay, J.; McCulloch, I.; Owens, R. M.; Inal, S., Direct metabolite detection with an n-type accumulation mode organic electrochemical transistor. Science advances 2018, 4 (6), eaat0911. 2: Ohayon, D.; Nikiforidis, G.; Savva, A.; Giugni, A.; Wustoni, S.; Palanisamy, T.; Chen, X.; Maria, I. P.; Di Fabrizio, E.; Costa, P. M., Biofuel powered glucose detection in bodily fluids with an n-type conjugated polymer. Nature materials 2020, 19 (4), 456-463.
Preferential Location of Dopants in the Amorphous Phase of Oriented Regioregular Poly(3-hexylthiophene-2,5-diyl) Films Helps Reach Charge Conductivities of 3000 S cm?1(2022-10-09) [Poster]Doping polymer semiconductors is a central topic in plastic electronics and especially in the design of novel thermoelectric materials. In this contribution, we demonstrate that doping of oriented semi-crystalline P3HT films with the dopant tris(4-bromophenyl)ammoniumyl hexachloroantimonate), also known as magic blue (MB), helps reach charge conductivities of up to 3000 S/cm and thermoelectric power factors (PF) of the order of 170±30 mW/mK2 along the polymer chain direction. A combination of transmission electron microscopy (TEM), polarized optical absorption spectroscopy and thermoelectric property measurements helps clarify the conditions necessary to achieve such high charge conductivities. The mechanism of doping is intimately related to the semi-crystalline structure of the polymer and whether crystalline, amorphous or both phases are doped. In the case of MB, mainly amorphous P3HT domains are doped while the structure of crystalline P3HT domains is almost unaltered by doping. A comparison with other dopants such as FeCl3, F4TCNQ, F6TCNNQ and Mo(tdf-COF3)3 indicates that the highest charge conductivities are obtained when the only amorphous phase of P3HT is preferentially doped. Charge transport improves in the sequence: i) doping of the only crystalline phase (F6TCNNQ and F4TCNQ), ii) doping of both crystalline and amorphous phases (FeCl3, Mo(tdf-COF3)3) and iii) doping of the only amorphous phase (Magic blue).