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 cm) and 21.76 % (14.0 cm). Moreover, these devices exhibit outstanding long-term stability, retaining 95 % of their initial efficiency after operation for 1000 hours at the maximum power point.