Page 18 - Read Online

Wang et al. Energy Mater. 2026, 6, 600064 Page 11 of 34

furan-2-ylmethanaminium chloride (FuMACl) alongside two-dimensional perovskite crystal seeds [109] .
Rather than simply passivating existing imperfections, these two-dimensional seeds function as dispersed
nucleation templates within the bulk precursor solution. Dynamic light scattering (DLS) measurements
reveal that these templates aggregate precursor components into significantly larger clusters, substantially
lowering the thermodynamic Gibbs free energy barrier for nucleation [109] . This strategically modulated
crystallization produces highly crystalline and vertically oriented perovskite grains. Complementing these
internal chemical engineering strategies, recent investigations have introduced an effective environmentally
assisted repair protocol that utilizes controlled oxygen exposure to target specific chemical vulnerabilities at
the grain boundaries. Advanced time-resolved photoemission electron microscopy (TR-PEEM) has revealed
that these boundary defect clusters are predominantly composed of a high density of interstitial iodine [110] .
These interstitial iodine species act as severe deep-level traps that capture photogenerated holes over an
extended spatial range through a rapid diffusion-assisted process. When the fully formed perovskite film is
exposed to small doses of dry air under continuous visible light illumination, the introduced oxygen
specifically interacts with these interstitial iodine-rich clusters. This photochemical reaction effectively
deactivates the hole-trapping capability of the interstitial iodine and neutralizes the most detrimental
boundary defects. By permanently eliminating this primary channel for non-radiative recombination, this
mechanism provides a robust post-crystallization refinement pathway to restore the local electronic integrity
of the polycrystalline lattice. It is important to note, however, that while the oxygen-assisted repair protocol
demonstrates significant efficacy for lead-based perovskites, its application is strictly precluded in
narrow-bandgap tin-lead mixed systems. In these compositions, the bivalent tin cations are
thermodynamically unstable and highly susceptible to rapid oxidation into the tetravalent state upon
exposure to even trace amounts of oxygen. This oxidation cascade induces severe p-type self-doping and
generates a high density of deep-level trap states that severely degrade carrier dynamics. Consequently, the
defect management paradigm must shift when transitioning to tin-containing frameworks. Rather than
relying on oxidative healing, these sensitive systems necessitate the stringent exclusion of oxygen alongside
the incorporation of robust reducing agents and oxidative inhibitors. As previously highlighted, alternative
strategies utilizing sacrificial metallic tin powder to reverse oxidation, or employing multifunctional organic
molecules such as melamine to provide sustained coordination-driven oxidative inhibition, are essential to
preserve both the structural and electronic integrity of the narrow-bandgap lattice.

Interface defects

Interface defects at the perovskite-CTL junction act as detrimental recombination centers that severely
impede device efficiency. While metal oxide layers including tin dioxide (SnO ) [111] , titanium dioxide
2
(TiO ) [112,113] , and zincite (ZnO) [114] are widely employed to enhance interfacial stability, phosphonic
2
acid-based self-assembled monolayers such as [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid
(Me-4PACz) have emerged as superior organic alternatives that form robust chemical bonds to improve
energy-level alignment. However, the practical application of Me-4PACz is frequently hindered by its
polarity-induced aggregation and the resulting poor wettability of perovskite precursor solutions, which
prevents the formation of a homogeneous buried interface [115] . To overcome these limitations, current
research has focused on a co-self-assembled monolayer strategy. By introducing co-assembled modifiers
such as 9H,9′H-[3,3′-bicarbazole]-9,9′-diylbis(butane-4,1-diyl))diphosphonic acid (DCZ-4P) and
4,4',4''-nitrilotribenzoic acid (NA), additional phosphonic acid or carboxyl anchoring groups are
incorporated to strengthen interfacial bonding and optimize precursor wettability, directly inspiring
researchers to develop vertical molecular bridge architectures [116,117] . Operating through a targeted
bifunctional mechanism, 4-bromobenzylphosphonic acid (4Br-BPA) utilizes its phosphonic acid functional
groups to anchor onto the underlying non-stoichiometric nickel oxide (NiO ) substrate . Simultaneously,
[118]
x
strong dipole-dipole interactions between the bridging molecule and adjacent organic species induce a lateral