Insights Into the Role of π‐Electrons of Aromatic Aldehydes in Passivating Perovskite Defects

Carbonyl‐containing aromatic ketones or aldehydes have been demonstrated to be effective defect passivators for perovskite films to improve performances of perovskite solar cells (PSCs). It has been claimed that both π‐electrons within aromatic units and carbonyl groups can, separately, interact with ionic defects, which, however, causes troubles in understanding the passivation mechanism of those aromatic ketone/aldehyde molecules. Herein, we clarify the effect of both moieties in one molecule on the defect passivation by investigating three aromatic aldehydes with varied conjugation planes, namely, biphenyl‐4‐carbaldehyde (BPCA), naphthalene‐2‐carbaldehyde (NACA) and pyrene‐1‐carbaldehyde (PyCA). Our findings reveal that the π‐electrons located in the conjugated system do not directly present strong passivation for defects, but enhance the electron cloud density of the carbonyl group augmenting its interaction with defect sites; thereby, with the extended conjugation plane of the three molecules, their defect passivation ability is gradually improved. PSCs incorporating PyCA with the most extended π‐electrons delocalization achieve maximum power conversion efficiencies of 25.67% (0.09 cm²) and 21.76% (14.0 cm²). Moreover, these devices exhibit outstanding long‐term stability, retaining 95% of their initial efficiency after operation for 1000 hours at the maximum power point.