Abstract
Chemical modification by co-solvents added to [6,6]-Phenyl-C71 butyric acid methyl ester, commonly known as an n-type semiconducting fullerene derivative PC70BM, is reported to change the electrical and thermoelectric properties of this system. Power factor of the casted PC70BM samples achieves values higher than that determined for a variety of organic compounds, including conducting polymers, such as PEDOT:PSS in the pristine form. After chemical functionalization by different solvents, namely N,N-Dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-Methyl-2-pyrrolidone (NMP), acetonitrile (AC), and 1,2-Dichloroethane (DCE), the four-probe in-plane electrical conductivity and Seebeck coefficient measurements indicate a simultaneous increase of the electrical conductivity and the Seebeck coefficient. The observed effect is more pronounced for solvents with a high boiling point, such as N,N-Dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and N-Methyl-2-pyrrolidone (NMP), than in acetonitrile (AC) and 1,2-Dichloroethane (DCE). We identified the origin of these changes using Hall mobility measurements, which demonstrate enhancement of the PC70BM charge carrier mobility upon addition of the corresponding solvents due to the improved packaging of the fullerene compound and chemical interaction with entrapped solvent molecules within the layers.
Highlights
Thermoelectric materials are very effective at turning a temperature difference directly into electricity
To find out how the mixed solvents affect the morphology of the PC70 BM samples, we investigated the sample surface by using an atomic force microscope (AFM)
Using the procedure of mixed-solvents for the PC70BM, we have demonstrated that both thermoelectric parameters, electrical conductivity, and the Seebeck coefficient can be manipulated in such a way that a simultaneous enhancement of both factors can be achieved
Summary
Thermoelectric materials are very effective at turning a temperature difference directly into electricity These materials can contribute to both cooling and thermoelectric power generation [1,2]. Crystals 2018, 8, 237 simultaneously, while keeping κ constant This is a challenging task as an increase in the number of carriers from doping will sacrifice Seebeck coefficient. One way towards improving ZT is to make use of chemical functionalization that increases mobility in the material, maintaining a constant number of carriers, which in turn leads to improving both electrical conductivity and Seebeck coefficient, according to the equation σ = enμ, where e is the electron charge, n is the charge carrier density, and μ is the carrier mobility [8]. The following section contains experimental details related to preparation of the samples, determination of their electrical conductivity, Seebeck coefficients, and charge carrier mobility, followed by a discussion of achieved results
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