Quantification of Ion Migration in CH3NH3PbI3 Perovskite Solar Cells by Transient Capacitance Measurements

TL;DR

This study quantifies ion migration in MAPbI3 perovskite solar cells using transient capacitance measurements, revealing ion species, their concentrations, diffusion coefficients, and activation energies to better understand device degradation.

Contribution

It provides the first detailed quantification of mobile ion species, their properties, and phase-dependent behavior in MAPbI3 perovskite solar cells, advancing understanding of ion migration effects.

Findings

Identified three migrating ion species, including iodide and methylammonium.

Mobile MA+ ions have higher concentration but lower diffusion coefficient than I- ions.

Activation energy for I- ions is consistent across devices, while MA+ activation energy varies with fabrication.

Abstract

Solar cells based on organic-inorganic metal halide perovskites show efficiencies close to highly-optimized silicon solar cells. However, ion migration in the perovskite films leads to device degradation and impedes large scale commercial applications. We use transient ion-drift measurements to quantify activation energy, diffusion coefficient, and concentration of mobile ions in methylammonium lead triiodide (MAPbI3) perovskite solar cells, and find that their properties change close to the tetragonal-to-orthorhombic phase transition temperature. We identify three migrating ion species which we attribute to the migration of iodide (I-) and methylammonium (MA+). We find that the concentration of mobile MA+ ions is one order of magnitude higher than the one of mobile I- ions, and that the diffusion coefficient of mobile MA+ ions is three orders of magnitude lower than the one for mobile I- ions. We furthermore observe that the activation energy of mobile I- ions (0.29 eV) is highly reproducible for different devices, while the activation energy of mobile MA+ depends strongly on device fabrication. This quantification of mobile ions in MAPbI3 will lead to a better understanding of ion migration and its role in operation and degradation of perovskite solar cells.