Reversible Ionic Migration into Transport Layers

Determine whether mobile ionic charges migrate reversibly into the transport layers of perovskite solar cells on timescales relevant to transient ion current measurements.

Background

The paper examines why transient ion current measurements of n-i-p perovskite solar cells can yield apparent ion densities above the capacitive limits predicted for transport layers. One proposed explanation is that ionic species are not confined to the perovskite absorber but can enter the transport layers, thereby increasing the electrically accessible ionic charge and extending the measurement’s sensitivity.

In-situ biasing time-of-flight secondary-ion mass spectrometry detects iodide within the Spiro-OMeTAD hole-transport layer and lithium within the SnO₂ electron-transport layer. However, the measurements do not determine whether these ionic species migrate reversibly into and out of the transport layers during the transient-ion-current timescale, as opposed to reflecting irreversible diffusion, degradation, or more complex interfacial electrochemistry.

References

While our ToF-SIMS measurements cannot establish whether mobile ionic charges migrate reversibly into the TLs, the presence of ionic species across other layers suggests that, in this case, ionic conductivity is perhaps not strictly confined to the perovskite absorber.

— Overcoming Transport Layer Bottlenecks to Quantify Ionic Parameters from Transient Ion Current Measurements of Perovskite Solar Cells  (2609.10438 - Jiao et al., 9 Sep 2026) in Section 2, subsection “HTL doping variation of n-i-p devices,” paragraph discussing in-situ biasing ToF-SIMS measurements