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Wang et al. Energy Mater. 2026, 6, 600064 Page 15 of 34

and flexible rotatable linkers. Upon deposition onto the perovskite surface, the electron-rich functional
groups of PY-IT, particularly its cyano and carbonyl moieties, function as Lewis bases that firmly coordinate
with undercoordinated Pb , effectively passivating defects across both the top surface and adjacent grain
2+
boundaries. Driven by its unique topological features, PY-IT spontaneously self-arranges to adopt a face-on
orientation. This polymeric network not only physically seals the vulnerable perovskite boundary but also
leverages its rotatable linkers to insert deeply into grain boundaries, thereby establishing a continuous
electron transfer channel. Furthermore, through strong π-π interactions with the subsequent fullerene-based
ETL, this multifunctional polymeric interlayer synergistically suppresses non-radiative recombination and
optimizes energy-level alignment, thereby maintaining ≈80% of its initial PCE after 1,000 h of simulated
1-sun illumination under maximum power point tracking (MPPT) .
[134]

Hydrophobic barriers
Beyond the intrinsic chemical vulnerabilities addressed through crystallization control, such as the rapid
oxidation of divalent tin, a review of the current literature reveals that the long-term operational stability of
these devices is predominantly challenged by extrinsic environmental stressors. Among these, moisture
remains the primary driver of severe perovskite degradation . Although recent literature proposes utilizing
[135]
the targeted SAM 4-(9H-carbazol-9-yl)phenylboronic acid (4PBA) to replace hygroscopic and acidic hole
transport materials such as poly(3,4-ethylenedioxythiophene):poly(styrenesulphonic acid) (PEDOT:PSS), the
latter remains the predominantly utilized option in narrow-bandgap tin-lead perovskite systems [136] .
Proponents of 4PBA highlight that its boronic acid group provides robust coordination anchoring to
eliminate acidic corrosion while its hydrophobic backbone effectively blocks moisture infiltration to extend
device lifetime. However, this hydrophobicity, originating from the peripheral carbazole group, introduces a
critical fabrication challenge. While constructing a formidable moisture barrier, this hydrophobic nature
directly induces severe dewetting of the highly polar perovskite precursor solution at the interface. The
precursor droplets readily shrink and agglomerate, causing the resulting perovskite film to exhibit numerous
pinholes and extensive areas of exposed substrate. Consequently, the pursuit of enhanced interfacial stability
inadvertently compromises device scalability and manufacturing reproducibility. Furthermore, the
self-assembly process of molecules like 4PBA is highly sensitive to the pretreatment state of the substrate,
relying heavily on the specific spatial distribution and density of surface hydroxyl groups. If the surface
activation of the conductive glass substrate exhibits microscopic inhomogeneity, the organic monolayer will
suffer from localized aggregation and generate unmodified voids. These spatial discontinuities inevitably
allow direct physical contact between the perovskite layer and the underlying bare oxide, triggering severe
interfacial non-radiative recombination and uncontrollable leakage currents. As a result, rather than
improving operational efficiency, these structural imperfections degrade the Voc of the photovoltaic devices.
Currently, the predominant approach to combat moisture-driven degradation relies on the integration of
highly hydrophobic molecules. For instance, Sharma et al. applied alkylamine hydrochlorides of varying
[137]
carbon chain lengths to successfully transform the perovskite surface from a hydrophilic state to a highly
hydrophobic one, thereby achieving stable operational performance for over 1,500 h under 35%-40% relative
humidity conditions. However, directly employing these strongly hydrophobic species inevitably encounters
the same manufacturing paradox previously discussed regarding the 4PBA monolayer. The inherent conflict
between constructing a robust moisture barrier and maintaining adequate precursor wettability severely
limits device scalability and manufacturing reproducibility. To overcome this fundamental bottleneck, future
research should leverage ML algorithms and high-throughput computational screening to discover novel
molecular alternatives that simultaneously guarantee exceptional environmental stability without sacrificing
large-area film scalability and device efficiency.