Overcoming ionic migration in perovskite solar cells through alkali metals

Alkali metals, as additives in perovskite solar cells (PSCs), have been extensively investigated for their impact on performance enhancement. This performance is sensitive to ion-driven interfacial recombination processes that lead to voltage losses and perform with negative capacitance features in impedance spectroscopy (IS). In this study, we exploited negative capacitance as a tool to systematically investigate the influence of Li, Na, and K on the photovoltage of the wide band-gap material MAPbBr3, known for historical photovoltage losses. Sodium cations were found to mitigate adverse interfacial recombination pathways, yielding a remarkable stabilized open-circuit potential of 1.65 V. Impedance measurements indicated sodium significant influence within the material's bulk, corroborated by time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy. These techniques confirmed the ability of Na to decrease ionic migration in perovskite materials. X-ray photoelectron spectroscopy (XPS) revealed the underlying mechanism by which Na accomplishes this task: through an electrostatic interaction with the organic compounds.