Charge Transport, Dielectric Response, and Magnetoconductance in Organic Diodes Based on a Novel P18-8 Conjugated Polymer for Magnetic Sensor Applications

This paper reports the use of P18-8, a novel conjugated polymer combining poly-(1,4-phenylene-ethynylene) and poly-(1,4-phenylene-vinylene), in the fabrication of an organic diode with the structure ITO/PEDOT:PSS/P18-8/LiF/Al. The electrical properties of the fabricated device were characterized using impedance spectroscopy across a frequency range of 100 Hz to 1 MHz at various applied voltages. The current density-voltage (<i>J</i>-<i>V</i>) characteristic exhibited ohmic behavior at low applied voltages, while at higher voltages, it conformed to the space charge limited current (SCLC) theory. The impedance (<i>Z</i>*) of the device, as a function of frequency and bias voltage, was modeled using a single parallel resistor and capacitor network connected in series with a resistance. The dielectric loss (ε″) decreased with increasing frequency for all applied voltages, mainly due to deformation and relaxation polarization effects. Peaks in the dielectric loss tangent (tan-(δ)) around 10⁵ Hz indicated dipolar polarization behavior. The lower values of the real part of the complex electric modulus (<i>M</i>') observed at the low-frequency region were attributed to the long-range mobility of charge carriers. Additionally, the imaginary part of the complex electric modulus (<i>M</i>″) reached its maximum value at all applied voltages, resulting in a peak at a specific frequency. The frequency-dependent conductance (σ) demonstrated a power-law dependence (σ ∝ ω^s), where the value of ″s″ increased with applied voltage and exceeded unity. Furthermore, we report the observed magnetoconductance (MC) under a weak static magnetic field (<1 T) at room temperature. Positive MC is observed and reaches up to 0.8% at a magnetic field of 500 mT at room temperature. It is found that with the increase of the voltage, the MC effect decreases. Our analysis of the experimental data was conducted within the framework of the electron-hole (e-h) pair model, employing the Stochastic Liouville Equation.