Critical Role of Organoamines in the Irreversible Degradation of a Metal Halide Perovskite Precursor Colloid: Mechanism and Inhibiting Strategy

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Solution processability enables perovskite solar cells (PSCs) as a potentially advantageous candidate over the conventional vacuum-based photovoltaic technologies. Nevertheless, the stability issue of the metal halide perovskite (MHP) precursor colloids seriously retards the future industrialization of PSCs. Herein we elucidate the key role of organoamines─deprotonated organoamine cations─in the degradation of the most commercially promising formamidinium/methylammonium (FA + /MA + ) mixed cation MHP precursor and determine that the amine-cation reaction of FA-MA +, rather than MA-FA +, is the main route triggering the irreversible degradation process. Subsequently, based on Schiff-base reactions, aldehydes (such as formaldehyde, benzaldehyde, and 3-thenaldehyde) are used to eliminate organoamines for effective suppression of the irreversible degradation of precursors and passivation of H-vacancy traps in the resultant MHP thin films. Furthermore, the optimal benzaldehyde can lead to reduced grain-boundary density to enhance the power conversion efficiency of PSCs from 20.7% to 23.3% with simultaneous improvement in the operational stability.