Impedance Spectroscopy Tutorial
1. Introduction
Impedance Spectroscopy (IS) probes a device with a small sinusoidal voltage perturbation around a chosen DC operating point and measures the complex current response. The complex impedance is \(\displaystyle Z(\omega)=\frac{\tilde V(\omega)}{\tilde I(\omega)}\), from which we analyse \(\mathrm{Re}[Z]\), \(\mathrm{Im}[Z]\), magnitude \(|Z|\), and phase \(\phi\). In OghmaNano, IS is performed with the Frequency (FX) domain tools and produces both Bode (vs. frequency) and Nyquist (−Im vs. Re) plots. This tutorial shows how to set up the frequency mesh, run IS on a standard OPV/perovskite stack, and interpret the main features. The same methods shown in this tutorial can be applied to any device with electrical contacts including OFETs, Perovskite devices, sensors and lasers.
2. Getting started
From the New simulation tab in the file ribbon, open the New simulation window (see ??). Choose Organic solar cells, then pick a ready-made PM6:Y6_E6_0hrs demo device to start (see ??). We will use the FX domain tools to run IS around a nominal operating point.
3. Run the simulation & inspect impedance outputs
fx_real.csv, fx_imag.csv, fx_phi.csv).
With the device open, go to the Editors tab and select the FX domain editor (??). Configure your frequency mesh (next section), then run the simulation from the File ribbon. When the run completes, browse the Output tab to find IS data products (??). You can double-click files to plot them directly.
4. Frequency mesh & configuration
Use a logarithmic sweep that covers the processes you expect (e.g., \(10^0\)–\(10^6\) Hz for contact/transport RCs). Keep the AC amplitude small (e.g., 10–20 mV) to remain in the linear regime. Choose the DC operating point (bias or illumination) from the device’s standard configuration before launching the FX analysis.
5. Reading Bode & Nyquist plots
Double-click the IS outputs to view standard plots. The Nyquist plot (−Im vs. Re) often shows semicircles whose diameters relate to resistive elements; their characteristic frequency links to the associated capacitance via \(\tau=1/\omega_0\). The Bode plots show how \(\mathrm{Re}[Z]\), \(\mathrm{Im}[Z]\), and phase evolve with frequency.
fx_real.csv).
fx_imag.csv).
fx_phi.csv).
💡 Tasks: Explore how IS responds to physical changes (try factors of 3–10 for clear shifts):
- Change the series/contact resistance and observe the high-frequency intercept in Nyquist.
- Increase an interfacial capacitance (e.g., at ETL/HTL) and track the semicircle radius/peak shift.
- Alter carrier mobility in the active layer and note changes to mid-frequency features.
- Switch illumination level (dark → 1 sun) and compare IS—photogeneration can reshape the spectra.
- Narrow/widen the frequency range to ensure all arcs are captured (low-f ionic/transport, high-f contact).
✅ Expected results
- Higher series/contact resistance shifts the Nyquist intercept to larger Re(Z) and can compress high-f arcs.
- Increasing interfacial capacitance moves a semicircle peak to lower frequency (larger time constant \(\tau=RC\)).
- Reducing mobility often increases resistive components, enlarging arcs and shifting features to lower frequency.
- Under illumination, additional recombination/transport channels can introduce or reshape arcs.
- If a suspected arc sits outside your sweep, extending the frequency window usually reveals it.