Light Intensity Modulated Impedance Spectroscopy (LIMIS) in All-Solid-State Solar Cells at Open Circuit

TL;DR

This paper introduces Light Intensity Modulated Impedance Spectroscopy (LIMIS), a novel photo-impedance technique for analyzing all-solid-state solar cells at open circuit, providing improved insights into their resistive and capacitive properties.

Contribution

The study presents LIMIS as a new method combining IMVS and IMPS signals, offering corrected lifetime evaluations and addressing limitations of traditional impedance spectroscopy in solar cell characterization.

Findings

LIMIS spectra differ from traditional IS, revealing new features.

The method corrects lifetime estimates by combining IS and LIMIS data.

LIMIS provides potential metrics for assessing solar cell performance and stability.

Abstract

Potentiostatic impedance spectroscopy (IS) is a well stablished characterization technique for elucidating the electric resistivity and capacitive features of materials and devices. In the case of solar cells, by applying a small voltage perturbation the current signal is recorded and the recombination processes and defect distributions are among the typical outcomes in IS studies. In this work a photo-impedance approach, named light intensity modulated impedance spectroscopy (LIMIS), is first tested in all-solid-state photovoltaic cells by recording the individual photocurrent (IMPS) and photovoltage (IMVS) responsivity signals due to a small light perturbation at open-circuit (OC), and combining them: LIMIS=IMVS/IMPS. The experimental LIMIS spectra from silicon, organic, and perovskite solar cells are presented and compared with IS. An analysis of the equivalent circuit numerical models for total resistive and capacitive features is discussed. Our theoretical findings show a correction to the lifetimes evaluations by obtaining the total differential resistances and capacitances combining IS and LIMIS measurements. This correction addresses the discrepancies among different techniques, as shown with transient photovoltage. The experimental differences between IS and LIMIS (i) proves the unviability of the superposition principle, (ii) suggest a bias-dependent photo-current correction to the empirical Shockley equation of the steady-state current at different illumination intensities around OC and (iii) are proposed as a potential figure of merit for characterizing performance and stability of solar cells. In addition, new features are reported for the low-frequency capacitance of perovskite solar cells, measured by IS and LIMIS.