Studying the effect of EDAI passivation on surface defects in triple cation mixed halide perovskite with PEEM

Nanoscale defects in photovoltaic materials can significantly impact solar cell performances, and yet their small size and location at buried interfaces make them challenging to study. A nanoscale imaging technique capable of identifying different types of defect and assessing their impacts to device performance is highly desirable. Photoemission electron microscopy (PEEM) with low energy photons could provide the necessary resolution for such investigations. In this paper, we demonstrate the use of PEEM and photoemission spectroscopy techniques to investigate defects in perovskite films and evaluate the effect of ethylenediamine iodide (EDAI) surface passivation, one of the well-studied passivation techniques that is known to reduce open-circuit voltage losses and enhance power conversion efficiency. Photoemission spectra show that mid-gap defects are spatially distributed similarly in both passivated and unpassivated samples but exhibit significantly reduced photoemission intensity after passivation, indicating effective defect passivation. This reduction suggests that EDAI mitigates recombination losses, potentially improving device stability and efficiency. Additionally, we observe that these defects are active hole traps. Given the extreme sensitivity of perovskite to light exposure and the inherently low hole trapping signal (<5 %), we outline the methodology for extracting this very weak signal.