Acetylsalicylic acid as a crystallization modulator for one-step deposited MAPbI3 in inverted perovskite solar cells

Perovskite solar cells often suffer performance losses during continuous operation due to interfacial charge accumulation and ion migration-related effects. Here, acetylsalicylic acid (ASA) is introduced as an additive in the one-step deposition of CH 3 NH 3 PbI 3 (MAPbI 3 ) for inverted (p-i-n) devices. The effect of ASA is systematically examined by fabricating and characterizing solar cells prepared with different ASA concentrations in the perovskite precursor solution. An optimal ASA concentration of 0.5 mg/mL, yields a champion power conversion efficiency of 20.0% and increases the stabilized power output from 17.1% (reference) to 18.9% under continuous operation. Impedance spectroscopy reveals a reduced accumulation capacitance ( C 2 ) for the optimal ASA condition, consistent with mitigated interfacial accumulation and reduced ionic polarization under operating bias. ASA also modulates crystallization in a concentration-dependent manner, increasing grain and crystallite size at moderate concentration while excessive ASA (2.0 mg/mL) reduces grain size and causes a pronounced fill-factor loss. Optical measurements show increased photoluminescence intensity for ASA-treated films, consistent with suppressed non-radiative recombination. In addition, XRD indicates a lower relative PbI 2 signal for ASA-containing films. Despite the presence of polar (hydrophilic) functional groups in ASA, unencapsulated devices stored for 120 days show no additional degradation relative to the reference, with both device sets retaining ∼80% of their initial PCE .