CsCl interface-driven structural resilience of FAPbI₃ to humidity

Abstract

Despite their power conversion efficiencies reaching 28.0%, formamidinium lead iodide (FAPbI₃)-based perovskite solar cells (PSCs) suffer from moisture-induced phase degradation that initiates preferentially at the SnO₂/FAPbI₃ buried interface, yet the coupling between humidity exposure and thermal stress at the interface remains unclear. Here, we introduce a CsCl interlayer at the buried interface of n-i-p-structured PSCs and examine its role in reinforcing the structural resilience of FAPbI₃ against moisture at elevated temperature. This interfacial role is distinguished from the improved crystallinity of the pristine FAPbI₃ film that CsCl is already known to provide. The CsCl interlayer blocked the irreversible formation of Pb-O-related species and enabled partial reconversion of the moisture-driven δ-phase and PbI₂ back to the α-phase during post-exposure annealing. Sequential changes in the lattice bonding environment across the pristine, humidity-exposed, and post-exposure annealed films were analyzed by complementary X-ray diffraction, grazing-incidence X-ray diffraction, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy to elucidate the CsCl interlayer-induced stabilization mechanism in FAPbI₃.

Keywords

Perovskite solar cell / FAPbI₃ / CsCl / moisture stability / structural resilience / phase recovery

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