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Temperature dependent charge transport properties of organic bulk heterojunction (BHJ)formed by p-type π-conjugated polymer and PCBM acceptorare analysed by dc and ac measurements in a wide temperature rangeof 110-473 K. This temperature range includes thermodynamic glass transition temperature (Tg) of the system. A change from Ohmic conduction (J∝V) to space charge limited current conduction with a power law J∝Vm, m≥2at higher applied bias voltages is observed from current-voltage (J-V)characteristics. Carrier concentration (N) is calculated from capacitance–voltage (C–V) measurements taken at different temperatures. Room temperature mobility values at various applied bias voltages are in accordance with that obtained from transient charge extraction by linearly increasing voltage (CELIV) measurement. Sample impedance is measured over five decades of frequency by using lock-in detection method. This data is used to extract temperature dependence of carrier mobility (μ), and dc conductivity (sdc). Significant changes in temperature dependent carrier concentration, carrier mobility and conductivity aroundTg indicates a strong connection between charge transport properties and structural changes of the bulk heterojunction.
Figure 1: (a) Cole–Cole plot for various bias voltages at room temperature. The equivalent circuit in the inset is used to fit the experimental data. The solid lines are the fitting results and points are the experimental data. (b) Arrhenius plots of current density at various voltages in the injection limited region; solid lines are the Arrhenius fits below Tg. (c) Temperature dependent mobility evaluated from Cole–Cole plot. Solid line is a guide to eye. Inset shows the Arrhenius plot of mobility. (d) Arrhenius plot of dc conductivity.
[A. Sarkar, A. B. Rahaman and D. Banerjee,J. Phys. D: Appl. Phys.,51, (2018),095602 (1-10)]
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