Extracting meaning from ion migration in perovskite solar cells

Angus, Fraser (2026) Extracting meaning from ion migration in perovskite solar cells. PhD thesis, University of Glasgow.

Abstract

Perovskite solar cells (PSCs) have rapidly emerged as one of the most promising nextgeneration photovoltaic technologies, with certified power conversion efficiencies now exceeding 27%. Unlike conventional photovoltaic materials, metal-halide perovskites contain mobile ionic defects that fundamentally alter the underlying device physics. As a consequence, PSCs conduct both electronic and ionic charge. Ion migration has been widely linked to current–voltage hysteresis, performance variability, and long-term degradation. While considerable effort has focused on mitigating these effects, far less attention has been paid to the information that can be extracted from the presence and redistribution of mobile ions within operating devices.

In this thesis, ion migration is used as a diagnostic of internal device energetics and recombination dynamics. Central to this work is the Stabilise and Pulse (SaP) technique, which enables controlled manipulation of ionic redistribution within an operating solar cell. By altering the distribution of mobile ions within the device, SaP modulates the internal electric field and enables access to the flat-band condition, which, as shown here, is equivalent to the built-in potential in PSCs. Controlling ionic redistribution, therefore, provides a means to probe interfacial charge accumulation, recombination behaviour, and energetic alignment within the device.

Using this approach, we experimentally show, for the first time, that mobile ions can systematically enhance the open-circuit voltage of perovskite solar cells, relative to an equivalent ion-free device. This is achieved through ionic redistribution, which reduces minority-carrier accumulation at transport-layer interfaces and suppresses interfacial recombination. The magnitude of this enhancement depends on the surface recombination strength and the energetic alignment of the transport layers.

Applying the SaP methodology to devices incorporating self-assembled molecules reveals that the molecular dipole strength directly shifts the built-in potential in PSCs, confirming that the Fermi-level difference across the transport layers governs the internal potential drop. At the same time, excessively large dipole moments introduce interfacial barriers that lead to charge accumulation and limit current extraction via increased recombination at the interface.

Extending the Stabilise and Pulse analysis to Spiro-based systems further demonstrates that the spatial localisation of the highest occupied molecular orbital plays a decisive role in recombination dynamics and charge extraction. Contrary to conventional design assumptions, promoting direct charge injection does not necessarily improve performance, as it can limit the quasi-Fermi level splitting in perovskite solar cells and reduce the achievable open-circuit voltage. This highlights that control of interfacial recombination can be more important than maximising energetic overlap.

Taken together, these findings show that mobile ionic charge should not be regarded solely as a source of instability, but rather as a feature that reshapes the internal electrostatics of PSCs in a measurable, design-relevant way.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Supported by funding from the Engineering and Physical Sciences Research Council (EPSRC) and a School of Chemistry Scholarship, University of Glasgow.
• Subjects: Q Science > QD Chemistry
• Colleges/Schools: College of Science and Engineering > School of Chemistry
• Funder's Name: Engineering and Physical Sciences Research Council (EPSRC), School of Chemistry Scholarship, University of Glasgow
• Supervisor's Name: Cooke, Professor Graeme
• Date of Award: 2026
• Depositing User: Theses Team
• Unique ID: glathesis:2026-86050
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 22 Jun 2026 15:48
• Last Modified: 23 Jun 2026 10:01
• URI: https://theses.gla.ac.uk/id/eprint/86050

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