Improved free iodine capture by light-driven carbon-halogen bond cleavage in perovskite solar cells with dynamic self-healing ability

Abstract

Carbon-based hole layer-free perovskite solar cells (PSCs) have excellent performance in work function matching, hydrophobicity, electrical conductivity, and relatively low cost, which is a competitive alternative. However, internal defects dramatically affect the stability of PSCs. Especially the iodine vacancy defect of Pb-I terminal has a lower formation energy, which is easier to form and exist stably. In this work, a few additives of p-Bromoaniline (BrC₆H₄NH₂) were introduced to dynamically self-healing defects while capturing the migrating I⁻ ions in perovskite. Under outdoor illumination, most of the C-Br bonds in p-Bromoaniline are activated and broken, resulting in Br⁻ ions and aniline cations (C₆H₄NH₂⁺). As Br⁻ ions with a smaller radius preferentially adsorb and passivate the iodine vacancy at the Pb-I end. Additionally, the C₆H₄NH₂⁺ cation captured I⁻ ions migrating from the perovskite, preventing further chemical reactions of the halogen ions when exposed to light, thus improving the stability of the PSCs through a dual protection mechanism. Under light/dark conditions, by orchestrating the precise cleavage and subsequent reformation of C-X (X = Br, I) bonds, X⁻ ions can undergo repeated cycles to facilitate a dynamic, cyclic self-repair mechanism of iodine vacancy defects. The result revealed that photoelectric conversion efficiency (PCE) of p-Bromoaniline-modified PSCs increased from 13.46 % to 17.18 %. The unencapsulated PSCs maintained a steady-state output power of 83.7 % under AM 1.5 illumination for 40 days at room temperature and RH 60 %.