Doping Induced Transition from Space-Charge-Limited to Ohmic Conduction in P3HT-PMMA

• Published in: Journal of electronic materials 2023-11, Vol.52 (11), p.7645-7651
• Main Authors: Mandal, Sougata, Menon, Reghu
• Format: Article
• Language: English
• Subjects: Bias; Characterization and Evaluation of Materials; Charge transport; Chemistry and Materials Science; Doping; Electric potential; Electronics and Microelectronics; Equivalent circuits; Glass substrates; Instrumentation; Materials Science; Molecular weight; Nyquist plots; Optical and Electronic Materials; Original Research Article; Polymer blends; Polymethyl methacrylate; Relaxation time; Solid State Physics; Space charge; Spectrum analysis; Time constant; Voltage
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-023-10697-z

The charge transport mechanisms in poly(3-hexylthiophene)-poly(methyl methacrylate) [P3HT-PMMA] blends are investigated in terms of current density–voltage ( J–V ) characteristics and impedance spectroscopy studies. In the undoped sample, the J–V characteristics show two different transport mechanisms for low-voltage (ohmic) and higher-voltage (space-charge-limited) regions. However, after doping, the ohmic transport dominates over space-charge-limited conduction, as confirmed by J–V and Nyquist plot analysis. The resistive and capacitive contributions, relaxation time, and effective capacitance ( C eff ) values are calculated from fit parameters of an equivalent circuit model consisting of one resistor ( R ) and constant phase element (CPE) in parallel. The resistance and C eff values of the doped sample are decreased by a factor of 421 and 21.73, respectively. The relaxation time constant ( τ ) in the undoped sample is 1.75 μs, and it decreases to 19.7 ns in the doped sample. In the undoped sample, the difference in the value of τ , from low bias voltage (ohmic) to high bias voltage (space charge), shows the role of injected carriers, whereas τ remains unchanged in the doped sample.