Molecular Dynamics and Conductivity of a PTB7:PC71BM Photovoltaic Polymer Blend: A Dielectric Spectroscopy Study

Abstract

Molecular dynamics of a low-band gap polymer, poly­{[4,8-bis­[(2-ethylhexyl)­oxy]­benzo­[1,2-b:4,5-b′]­dithiophene-2,6-diyl]­[3-fluoro-2-[(2-ethylhexyl)­carbonyl]­thieno­[3,4-b]­thiophenediyl]} (PTB7), and its 1:1.5 wt blend with a fullerene derivative, [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM), accessible for organic photovoltaics was studied with the broadband dielectric spectroscopy (BDS) technique in a wide range of frequency (from 10–1 to 106 Hz) and temperature (from −130 to 150 °C). In the BDS spectra, three types of molecular mobility of the polymer chains designated as γ-, β1-, and β2-relaxations, along with conductivity and electrode polarization processes, were recognized, separated, and analyzed. The relaxation processes in PTB7 and PTB7:PC71BM were described with Arrhenius-type equations and related parameters were found. Their analysis allowed us to reveal the influence of the PC71BM molecules on the dynamics of the polymer chains. Based on dc conductivity data, the Cole–Cole diagrams for PTB7 and PTB7:PC71BM were plotted. They allowed for estimating the hole lifetime and its comparison with the hole extraction time.

Electric and Dielectric Properties in Low-Frequency Fields of Composites Consisting of Silicone Rubber and Al Particles for Flexible Electronic Devices

“…As can be seen from Figure 8 , at a constant volume fraction x, the conductivity spectrum, σ(f) consists of two regions: (1) a region in which σ tends to a constant value by decreasing the frequency (at very low frequencies, σ does not depend on frequency) corresponding to DC-conductivity (σ DC ); (2) a dispersion region, where σ rapidly increases with frequency, corresponding to AC-conductivity (σ AC ). A similar frequency dependence σ(f) was also observed for other composite samples, such as Cu 1+x Mn 1-x O 2 type composite materials (with x = 0–0.10) [ 33 ], or polymers of PTB7 type [ 34 ]. This behavior is in accordance with the Jonscher universal law [ 35 ]: …”

“…As seen in Figure 8 , in the first region of the low frequency range, the measured conductivity decreases slowly by the decrease of frequency, tending to a constant value, which will not depend on the frequency, representing the DC component of conductivity (σ DC ) according with the Jonscher universal law [ 35 ]. The numerical values of the DC conductivity were determined based on the Nyquist impedance diagrams, Z″(Z′) in Figure 5 b) and the fit parameters (see Table 1 ) corresponding to the equivalent electrical model for each sample [ 34 , 36 ]. As a result, the values thus obtained for σ DC are listed in Table 1 .…”

The effect of PbS quantum dots on molecular dynamics and conductivity of PTB7:PC71BM bulk heterojunction as revealed by dielectric spectroscopy

“…S2 (ESI †) demonstrates a smooth surface morphology with a root mean square value of 0.775 nm. This value is typical for PTB7:PC71BM:QD composite surfaces 9,15,18,19 and lower than that for the binary PTB7:PC71BM blend (5.45 nm 29 ). The discovered smooth surface indicates good compatibility in a three-component system, ensuring good contact between layers and low interface resistance to encourage charge extraction and transport.…”

“…In the literature, we found a few reports on molecular mobility of donor polymers in BHJ investigated using QENS [23][24][25][26] and BDS. [27][28][29] Comparing the capabilities of both methods, we should emphasize that the QENS technique could particularly be suitable for the analysis of small-scale molecular motions in the polymer because of a low and narrow timescale range (from 1 to 50 ps), whereas the BDS technique allows analyzing the mobility of polymer chains (from 10 À6 to 10 s). Besides, the BDS method can be used to study electrical conductivity, which is a valuable characteristic of a photovoltaic blends.…”

Liquid Metal Patterned Stretchable and Soft Capacitive Sensor with Enhanced Dielectric Property Enabled by Graphite Nanofiber Fillers

“…All contact angle measurements were carried out using goniometer SEO-Phoenix 300 (Surface Electro Optics Co., Ltd., Suwon, Korea). DC conductivity (σ dc ) of the samples were measured using KEYSIGHT 34461A benchtop multimeter (Keysight Technologies, Santa Rosa, California, USA) using the formula [67] given by Equation ( 1)…”