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Wang et al. Energy Mater. 2026, 6, 600064 Page 3 of 34

FUNCTIONS AND MECHANISMS OF ADDITIVES
Crystallization control for high-quality thin films
The formation of high-quality perovskite films is governed by a series of additive-driven interventions across
multiple stages, ranging from ordering colloidal distribution and tailoring intermediate phase selection to
controlling grain coarsening and nucleation. Each of these modulations is strategically engineered to
eliminate defects and optimize device performance.

Ordering colloidal distribution and stacking
At the earliest stage, perovskite inks are best understood as colloidal suspensions rather than ideal molecular
solutions. Their stability is primarily governed by the balance between electrostatic repulsion and van der
Waals attraction, which determines whether solute species remain dispersed or undergo uncontrolled
aggregation . Additives serve as colloidal stabilizers during this stage by suppressing spontaneous clustering
[42]
and homogenizing the level of supersaturation. A cornerstone strategy in this regulatory paradigm involves
the incorporation of tin(II) fluoride (SnF ), in which fluoride ions selectively coordinate with Sn species to
2+
2
mitigate oxidation-induced structural disorders and stabilize Sn-Pb inks . However, a critical mechanistic
[43]
trade-off underpins this canonical approach. While moderate SnF levels effectively passivate surface
2
Sn(IV)-associated deep traps and extend carrier lifetimes, stoichiometric excesses paradoxically induce the
stabilization of tin interstitial (Sn) defects. These Sn traps function as deleterious deep-level electronic states
i
i
that introduce non-radiative recombination pathways, thereby necessitating a delicate equilibrium in defect
management . To circumvent these limitations, diverse alternative strategies have been developed to
[44]
supplement or replace SnF . One direct approach is the use of sacrificial metallic Sn(0) powder, which
2
reduces Sn back to Sn without introducing foreign ionic impurities . A more versatile paradigm relies on
2+
4+
[45]
multifunctional organic additives such as melamine, gallic acid, or theophylline, which provide sustained
oxidative inhibition through robust C=N or C=O coordination [46,47] . In particular, melamine, acting as a
highly symmetric Lewis base, has been shown to strongly coordinate with Sn ions, effectively regulating the
2+
formation of iodostannate clusters and significantly enlarging colloidal dimensions. This molecular
interaction is instrumental in navigating a second fundamental trade-off that requires balancing the
intrinsically rapid nucleation typical of tin-halide perovskites with the necessity for sustained crystal growth.
By retarding crystallization kinetics and simultaneously inhibiting Sn oxidation, the melamine-coordinated
2+
system facilitates a more orderly crystal assembly. This synergistic effect minimizes defect-induced voltage
loss and enhances the overall PCE . The principle of colloidal and kinetic modulation further extends to
[48]
other advanced organic framework additives. For example, small-molecule deformable additives can reshape
the size distribution of colloids to decelerate crystallization while concurrently passivating defects to suppress
stress accumulation . In a similar vein, spatially isomeric fulleropyrrolidine derivatives illustrate how
[49]
tailoring the steric structure of additives can enlarge colloidal aggregates and optimize crystallization kinetics,
ultimately yielding highly uniform tin-based perovskites with low defect densities [Figure 1A].
[50]

Tailoring intermediate phase selection
Once the colloidal framework is stabilized, additives intervene in the nucleation and intermediate-phase
formation stage, where coordination chemistry and weak-anion interactions govern the transition from
solvation complexes to crystalline nuclei. The incorporation of weakly coordinating anions such as chloride
and thiocyanate facilitates the development of reversible halide-rich intermediates including HPbI Cl ,
3-x
x
which serve to homogenize nucleation and promote secondary recrystallization [51,52] . To precisely govern
these processes, a fast-solidification and slow-growth strategy can be employed using a volatile acetonitrile
solvent system in combination with non-volatile additives such as ammonium thiocyanate and
methylammonium chloride . The rapid evaporation of acetonitrile effectively freezes a uniform distribution
[51]
of nuclei during the initial solidification phase . Subsequently, the remaining high-boiling-point additives
[53]