Multilayer Capacitances: How Selective Contacts Affect Capacitance Measurements of Perovskite Solar Cells

TL;DR

This paper introduces a multilayer model to analyze how selective contacts in perovskite solar cells influence capacitance measurements, revealing fundamental limits and emphasizing the significant impact of contact capacitance on parameter extraction.

Contribution

The paper develops a simple multilayer series model that accounts for the resistive and capacitive effects of selective contacts, clarifying their influence on capacitance measurements in perovskite solar cells.

Findings

Capacitance measurements are significantly affected by contact capacitances.

Most experimental data fall within the model's fundamental limits.

Contact capacitance impacts the accuracy of doping and trap density estimations.

Abstract

Capacitance measurements as a function of voltage, frequency and temperature are useful tools to identify fundamental parameters that affect solar cell operation. Techniques such as capacitance-voltage (CV), Mott-Schottky analysis and thermal admittance spectroscopy (TAS) measurements are therefore frequently employed to obtain relevant parameters of the perovskite absorber layer in perovskite solar cells. However, state-of-the-art perovskite solar cells employ thin electron and hole transport layers that improve contact selectivity. These selective contacts are often quite resistive in nature, which implies that their capacitances will contribute to the total capacitance and thereby affect the extraction of the capacitance of the perovskite layer. Based on this premise, we develop a simple multilayer model that considers the perovskite solar cell as a series connection of the geometric capacitance of each layer in parallel with their voltage-dependent resistances. Analysis of this model yields fundamental limits to the resolution of spatial doping profiles and minimum values of doping/trap densities, built-in voltages and activation energies. We observe that most of the experimental capacitance-voltage-frequency-temperature data, calculated doping/trap densities and activation energies reported in literature are within these cut-off values derived, indicating that the capacitance response of the perovskite solar cell is indeed strongly affected by the capacitance of its selective contacts.