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Page 12 of 34 Wang et al. Energy Mater. 2026, 6, 600064

tightening effect that significantly densifies the transport layer. Its terminal Br atom then effectively
passivates the perovskite layer by coordinating with undercoordinated Pb . A parallel approach involves the
2+
2,5-thiophenedicarboxylic acid (TDCA), which similarly utilizes its carboxyl group to establish firm
anchoring to the NiO substrate while its upper functional moiety chelates undercoordinated Pb within the
2+
x
perovskite lattice [119] . While co-assembled surface modifiers successfully optimize interfacial chemistry and
precursor wettability at the organic layer surface, molecular bridges execute a three-dimensional stabilization
mechanism. Because their compact molecular architecture allows them to physically penetrate the existing
monolayer voids, they bypass the surface restriction to directly interlock the underlying metal oxide substrate
with the perovskite lattice. This vertical integration not only neutralizes chemical defects across all three
distinct layers but also provides a mechanical locking effect that actively resists interfacial delamination and
thermal stress. Consequently, although both methodologies significantly suppress non-radiative
recombination, the dual-anchoring nature of the molecular bridge provides an inherently more robust
foundation for achieving superior long-term operational stability in inverted photovoltaic devices.

Extended defects
Beyond atomic and mesoscale imperfections, extended defects such as secondary phases represent
macroscopic structural disruptions that undermine the overall electronic homogeneity of the perovskite film.
These defects typically originate from improper crystallization kinetics or an intentional excess of precursor
materials, which leads to the formation of secondary species that can either facilitate or obstruct charge
transport. A particularly prominent example is the secondary phase of PbI , which is frequently introduced
2
by maintaining a stoichiometric excess of approximately 5% in the precursor solution. Previous reports have
consistently demonstrated that this residual PbI plays a critical role in attaining high performance by
2
effectively passivating defects at the grain boundaries and surfaces through the formation of a type-I band
alignment [120,121] . However, the inherent chemical activity of excess PbI introduces a significant trade-off in
2
terms of long-term device durability [122-124] . Excessive or uncontrolled PbI is highly susceptible to
2
photodecomposition and facilitates ion migration, which ultimately results in severe device instability and
pronounced hysteresis in J-V characteristics [125,126] . To resolve this fundamental conflict, recent work has
focused on stabilizing these secondary phases through targeted chemical conversion. Zhao et al. [127]
demonstrated a targeted strategy by doping FAPbI perovskites with rubidium chloride (RbCl), effectively
3
converting the reactive PbI into an inactive compound identified as (PbI ) RbCl. Unlike pure PbI , this
2
2
2 2
RbCl-stabilized compound remains chemically inert under operational conditions while successfully
maintaining the desired passivation effects . This approach achieves a certified PCE of 25.6% and ensures
[127]
that devices retain 80% of their initial efficiency after 500 h of thermal stress at 85 °C. While the chemical
conversion of reactive secondary species represents an effective post-crystallization stabilization approach,
the fundamental suppression of extended macroscopic defects can also be achieved proactively by
controlling the initial crystallization kinetics. This kinetic control is particularly critical in highly reactive
systems where the rapid crystallization induced by conventional antisolvents (e.g., chlorobenzene (CB))
typically generates a high density of grain boundaries and unwanted secondary phases. To address this
challenge, Zhang et al. recently introduced the green antisolvent diethyl carbonate (DEC) to regulate the
[128]
solvent-antisolvent interactions during the formation of tin-based perovskite films. Time-dependent
steady-state absorption analyses reveal that DEC significantly retards the solvent extraction process to
provide a prolonged thermodynamic window for ordered crystal growth. This decelerated crystallization
promotes a highly preferred vertical crystal orientation and dramatically enlarges the average grain size
across the perovskite film. Because macroscopic grain boundaries represent the primary extended defects in
polycrystalline architectures, this morphological optimization directly suppresses their formation and
eliminates the associated deep-level trapping centers.