Thermoelectric Effect and Application of Organic Semiconductors

Human development and society progress require solving many pressing issues, including sustainable energy production and environmental conservation. Thermoelectric power generation looks like promising opportunity converting huge heat from the sun and waste heat from industrial sector, housing appliances and infrastructure and automobile and other fuel combustion exhaust directly to electrical energy. Thermoelectric power generation will be of high demand, when technology will be affordable, providing low price, high conversion efficiency, reliability, easy applicability and advanced ecological properties of end products. In this context, organic thermoelectric materials attract great interest caused by non-scarcity of raw materials, non-toxicity, potentially low costs in high-scale production, low thermal conductivity and wide capabilities to control thermoelectric properties. In this chapter, we focus mainly on thermoelectric effect in several organic semiconductors, both crystalline and disordered. We present theory of some transport phenomena determining thermoelectric properties of organic semiconductors, including general expression of thermoelectric effect, percolation theory of Seebeck coefficient, hybrid model of Seebeck coefficient, Monte Carlo simulation and first-principle theory. Finally, a future outlook of this field is briefly discussed

Possible Luttinger liquid behavior of edge transport in monolayer transition metal dichalcogenide crystals.

In atomically-thin two-dimensional (2D) semiconductors, the nonuniformity in current flow due to its edge states may alter and even dictate the charge transport properties of the entire device. However, the influence of the edge states on electrical transport in 2D materials has not been sufficiently explored to date. Here, we systematically quantify the edge state contribution to electrical transport in monolayer MoS2/WSe2 field-effect transistors, revealing that the charge transport at low temperature is dominated by the edge conduction with the nonlinear behavior. The metallic edge states are revealed by scanning probe microscopy, scanning Kelvin probe force microscopy and first-principle calculations. Further analyses demonstrate that the edge-state dominated nonlinear transport shows a universal power-law scaling relationship with both temperature and bias voltage, which can be well explained by the 1D Luttinger liquid theory. These findings demonstrate the Luttinger liquid behavior in 2D materials and offer important insights into designing 2D electronics

Limitation of the concept of transport energy in disordered organic semiconductors

A systematic study of transport energy in disordered organic semiconductors based on the variable range hopping theory is presented here. The temperature–, electric-field–, material-disorder–and carrier-concentration–dependent transport energy are discussed extensively. We demonstrate that the transport energy is not a general concept and is of limitation even in a low electric field and concentration regime

A Novel Method to Analyze the Relationship between Thermoelectric Coefficient and Energy Disorder of Any Density of States in an Organic Semiconductor

In this work, a unified method is proposed for analyzing the relationship between the Seebeck coefficient and the energy disorder of organic semiconductors at any multi-parameter density of states (DOS) to study carrier transport in disordered thermoelectric organic semiconductors and the physical meaning of improved DOS parameters. By introducing the Gibbs entropy, a new multi-parameter DOS and traditional Gaussian DOS are used to verify this method, and the simulated result of this method can well fit the experiment data obtained on three organic devices. In particular, the impact of DOS parameters on the Gibbs entropy can also influence the impact of the energy disorder on the Seebeck coefficient