IMPS Simulation Tutorial

1. Introduction

IMPS (Intensity-Modulated Photocurrent Spectroscopy) measures how a device’s photocurrent responds to a small sinusoidal modulation of the incident light. Sweeping frequency yields a complex transfer function whose magnitude and phase carry information about carrier transport, recombination, and interfacial processes. With OghmaNano you can simulate IMPS directly on your device model to generate Nyquist and Bode plots that mirror experiment.

2. Getting started

Open the New simulation window (see Figure 1a) and double-click the IS/IMPS/IMVS/CV category to browse frequency-domain examples (see Figure 1b). Load an IMPS template to get a ready-to-run project with sensible defaults.

New simulation window with categories including IS/IMPS/IMVS/CV. — *New simulation* window—select the **IS/IMPS/IMVS/CV** group.

List of IMPS/IMVS/IS example templates. — Example templates for frequency-domain studies. Choose an **IMPS** setup.

3. Configure & run IMPS

Simulation type ribbon with IMPS highlighted. — **Simulation type** ribbon with **IMPS** selected.

Main OghmaNano window showing the device structure scene. — Main device window—run IMPS from here once the experiment is configured.

Open the Frequency domain experiment window and set your frequency mesh (??). For IMPS, use Excite with: Light and Measure: Current (short-circuit by default). Choose a modulation depth that keeps you in the small-signal regime. When ready, click Run simulation.

Frequency mesh editor with segments and colored sample points across decades. — **Frequency mesh.** Define start/stop and density per segment.

Bode-style IMPS plot showing the real component of photocurrent versus frequency. — **Real(I) vs frequency.** One view of the current response spectrum.

Bode-style IMPS plot showing the imaginary component of photocurrent versus frequency. — **Imag(I) vs frequency.** Complements the real part to reveal time constants.

4. Inspecting the outputs

IMPS produces a Nyquist plot (Imag vs Real photocurrent) and Bode plots vs frequency (e.g. Real/Imag and Phase). The Nyquist locus often forms an arc; its characteristic frequency is linked to recombination/transport times. The phase plot helps separate capacitive storage from kinetic limits.

IMPS Nyquist plot: Imaginary(I) vs Real(I) with frequency annotations. — **Nyquist (IMPS).** Imag(I) vs Real(I) with frequency markers.

Phase of photocurrent response versus frequency (IMPS). — **Phase(I) vs frequency.** Phase lag highlights storage and recombination delays.

Output tab listing IMPS result files written by the simulation. — **Outputs.** Find CSVs and plots in the *Output* tab for post-processing.

💡 Tasks: Probe sensitivity with these tweaks (start small; then try ×10 changes):

Shift the frequency mesh lower/higher to expose slow traps or fast transport.
Reduce the light modulation depth to stay in small-signal (linear) regime.
Alter recombination or interfacial parameters and watch the Nyquist arc shift in size/position.
Compare IMPS on devices with different transport layers to see which bottleneck dominates.

✅ Expected results

A clear Nyquist arc; the apex frequency tracks a dominant recombination/transport time constant.
Lower recombination rate → arc moves to lower frequencies; magnitude may increase.
Stronger capacitive effects → larger phase lag and broader low-frequency features.
Mesh extending to lower f reveals slow processes; higher f highlights fast transport limits.