Research Paper: Equivalent-circuit modeling of electron-hole recombination in semiconductors and mixed ionic-electronic conductors

Scientific Summary

This study addresses the critical need for a general equivalent circuit model of electron-hole recombination in semiconductors and mixed ionic-electronic conductors. The main goal was to formally introduce and integrate accurate circuit elements for radiative and nonradiative recombination into a transmission-line model, analytically equivalent to linearized drift-diffusion equations. The research specifically derived analytical solutions for bulk and interfacial polarization effects, crucial for understanding complex device responses like those in halide perovskite solar cells.

The study established that resistors accurately model radiative recombination, while bipolar transistors are the general, accurate representation for nonradiative recombination in the small-signal regime, simplifying to resistive elements only in specific cases. A key finding is that the influence of mobile ions in mixed conductors significantly dictates the frequency-dependent electronic response at low frequencies by altering the electrostatic potential, extending the concept of ionic-to-electronic current amplification. The models successfully reproduce complex impedance spectra, demonstrating transitions between ion conductor (IC) and mixed conductor (MC-i) approximations, and explaining capacitive or inductive behaviors stemming from dominant recombination processes.

Why it matters

This work offers a comprehensive, analytically accurate platform for interpreting electrical responses of semiconducting and mixed ionic-electronic conducting devices, particularly for halide perovskite solar cells where mobile ion effects complicate analysis. By providing accessible models with analytical solutions, it facilitates the experimental investigation and data fitting of complex impedance spectra, revealing underlying physical properties and recombination mechanisms.

Publication Details

Moia, D. (2025), Equivalent-circuit modeling of electron-hole recombination in semiconductors and mixed ionic-electronic conductors. Physical Review Applied, 23: 014055. https://doi.org/10.1103/PhysRevApplied.23.014055.

Why it matters (Broader Impact of Methodology)

The methodology presented provides a general platform for studying the electrical response of various semiconductor devices under different biases, moving beyond empirical models. It enables a more general physical interpretation of solar cell behavior, including parameters like the ideality factor, and supports the analysis of other time- and frequency-domain measurements. This framework is also extensible to account for additional complexities such as multiple mobile ionic species, nonideal contacts, and redox reactions, broadening its applicability across photoelectrochemical devices.