Dion-Jacobson Perovskites

• Dion-Jacobson perovskites are layered structures characterized by a single divalent spacer that bridges adjacent slabs, ensuring stronger interlayer connectivity.
• They exhibit tunable optical and electronic properties, where variations in slab thickness and octahedral tilting affect band gaps and exciton-phonon interactions.
• Their enhanced transport, stability, and light‐management properties make them promising for applications in photovoltaics, photonics, and ferroelectric devices.

Dion–Jacobson perovskites are layered perovskites in which adjacent perovskite slabs are separated by a single interlayer cation layer rather than the bilayer arrangement characteristic of Ruddlesden–Popper phases. In contemporary halide-perovskite research, the term usually denotes two-dimensional hybrid organic–inorganic metal-halide perovskites in which divalent diammonium spacers bridge neighboring inorganic slabs, with general formulas such as $$\mathrm{A'}\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$ and, for the $n=1$ lead-iodide case, $\mathrm{A'}\mathrm{PbI}_4$. In oxide chemistry, Dion–Jacobson phases instead denote layered perovskites with primitive stacking of perovskite blocks separated by a single layer of monovalent interlayer cations, as in $\mathrm{A}R\mathrm{B}_2\mathrm{O}_7$ for $n=2$ niobates. Across these contexts, the defining motif is tighter interlayer connectivity than in RP analogues, and that connectivity propagates into band structure, exciton physics, transport, magnetism, ferroelectricity, and device stability (Coriolano et al., 2023, Asensio et al., 2024, Asaki et al., 2020).

1. Structural definition and phase taxonomy

In layered hybrid halide perovskites, DJ and RP phases differ first in the valence and topology of the spacer cation. RP phases use monovalent spacers and, for single-layer structures, follow $(A^+)_{2}MX_4$ or $$(\mathrm{A'})_2\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$; neighboring octahedral sheets are separated by two organic layers and a van der Waals gap. DJ phases use divalent spacers, written as $(\mathrm{A'}^{2+})MX_4$ or $$\mathrm{A'}\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$, so that a single diammonium cation bridges two adjacent slabs through two terminal ammonium groups. The resulting inorganic–organic–inorganic linkage removes the van der Waals gap and typically shortens the interlayer distance relative to RP analogues (Coriolano et al., 2023, Asensio et al., 2024, Zheng et al., 2023).

Context	Representative formula	Defining interlayer motif
Hybrid halide DJ	$$\mathrm{A'}\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$, $n=1$0	One divalent spacer layer bridging adjacent slabs
Hybrid halide RP	$n=1$1, $n=1$2	Two monovalent spacer layers with van der Waals coupling
Oxide DJ	$n=1$3	Single interlayer cation layer and primitive slab stacking

The structural distinction is not purely nominal. In hybrid halides, DJ phases are described as having better out-of-plane connectivity, stronger inorganic–organic coupling, and shorter interlayer distances than RP phases, which is why they are repeatedly treated as favorable platforms for enhanced transport and stability. In oxide DJs, primitive stacking rather than RP-type body-centered slab stacking governs the allowed octahedral rotation patterns and, consequently, the symmetry-breaking routes to ferroicity (Coriolano et al., 2023, Asaki et al., 2020).

A further refinement is that the DJ–RP distinction can be treated as continuous rather than binary. The layer shift factor $n=1$4 quantifies the in-plane displacement between neighboring slabs; DJ end members correspond to $n=1$5 and $n=1$6, whereas the RP end member is $n=1$7. Analysis of 282 (100)-oriented layered hybrid halide perovskites showed that real structures populate the full configuration space rather than clustering only at ideal DJ or RP points, and monoammonium versus diammonium chemistry does not by itself impose a unique layer shift (Marchenko et al., 2020).

2. Structural descriptors and structure–property relations

For halide DJs, local octahedral geometry is a primary control parameter. In $n=1$8 lead-iodide DJs based on 1,6-hexamethylenediammonium (HE) and 3-(dimethylamino)-1-propylammonium (DMPA), the distance between inorganic layers decreases from 11.359 Å in HEPbI$n=1$9 to 10.580 Å in DMPAPbI$\mathrm{A'}\mathrm{PbI}_4$0 phase 1 and 10.387 Å in DMPAPbI$\mathrm{A'}\mathrm{PbI}_4$1 phase 2, while the in-plane Pb–I–Pb angle increases from $\mathrm{A'}\mathrm{PbI}_4$2 in HE to $\mathrm{A'}\mathrm{PbI}_4$3 in DMPA(2) and $\mathrm{A'}\mathrm{PbI}_4$4 in DMPA(1). The same study defines an NH penetration depth $\mathrm{A'}\mathrm{PbI}_4$5, with smaller values corresponding to deeper penetration and stronger local distortion; the reported trend is that larger NH penetration, expressed as smaller $\mathrm{A'}\mathrm{PbI}_4$6, gives stronger tilt and smaller Pb–I–Pb angle (Coriolano et al., 2023).

These structural changes correlate monotonically with optical energies. In the same DJ series, DMPA(1) with Pb–I–Pb $\mathrm{A'}\mathrm{PbI}_4$7 emits at 2.21 eV, DMPA(2) with $\mathrm{A'}\mathrm{PbI}_4$8 at 2.30 eV, and HE with $\mathrm{A'}\mathrm{PbI}_4$9 at 2.50 eV. The reported interpretation is that increased tilt reduces Pb–I orbital overlap, enhances bonding–antibonding splitting, and widens the band gap, so smaller Pb–I–Pb angles produce blue-shifted excitonic photoluminescence (Coriolano et al., 2023).

A broader geometric descriptor is the LSF-based slab registry. In hypothetical single-layer $\mathrm{A}R\mathrm{B}_2\mathrm{O}_7$0, the band gap increases monotonically as the layer shift moves from DJ-like $\mathrm{A}R\mathrm{B}_2\mathrm{O}_7$1 toward RP-like $\mathrm{A}R\mathrm{B}_2\mathrm{O}_7$2. That trend is attributed to decreasing overlap of axial $\mathrm{A}R\mathrm{B}_2\mathrm{O}_7$3-orbitals for terminal halogens in adjacent layers, and it formalizes a point that older DJ/RP labels often left qualitative: the electronic consequences of interlayer registry can be quantified continuously rather than only by family names (Marchenko et al., 2020).

Thickness $\mathrm{A}R\mathrm{B}_2\mathrm{O}_7$4 is a second structural axis. Kinetically controlled space confinement yielded phase-pure 3AMP-based DJ crystals with $\mathrm{A}R\mathrm{B}_2\mathrm{O}_7$5, whose absorption band gaps are 1.95, 1.88, 1.82, and 1.75 eV and whose PL peaks are 1.90, 1.82, 1.79, and 1.75 eV, respectively. This gives an explicit DJ thickness series in which increasing slab thickness reduces confinement and red-shifts both absorption and emission (2212.00989).

3. Excitons, exciton–phonon coupling, and interlayer carrier transport

In $\mathrm{A}R\mathrm{B}_2\mathrm{O}_7$6 DJ lead iodides, excitons are described as Wannier-like, but strongly confined, with strong quantum and dielectric confinement arising from single-octahedron inorganic layers embedded between low-$\mathrm{A}R\mathrm{B}_2\mathrm{O}_7$7 organic spacers. Room-temperature polaritonic experiments directly show large oscillator strength through Rabi splittings of 100–125 meV, but the same confinement also amplifies exciton–phonon coupling and polaronic dressing (Coriolano et al., 2023).

Ultrafast spectroscopy on the rigid DJ perovskites (FPP)PbI$\mathrm{A}R\mathrm{B}_2\mathrm{O}_7$8 and (FPT)PbI$\mathrm{A}R\mathrm{B}_2\mathrm{O}_7$9 resolved coherent phonon bands centered near 45 and 50 cm$n=2$0, respectively, with dominant spectral weight in the 20–70 or 20–80 cm$n=2$1 range. The oscillatory transient-absorption component exhibits a node and a sharp $n=2$2 phase jump at the exciton resonance, the characteristic signature of frequency modulation by a displaced excited-state potential. Using a classical displaced harmonic oscillator model, the work extracted Huang–Rhys factors $n=2$3 for FPP and $n=2$4 for FPT, with reorganization energies $n=2$5 and $n=2$6 meV. DFT-based special-displacement analysis assigns the dominant coupling to low-frequency octahedral rocking and twisting modes in the 30–60 cm$n=2$7 range, establishing room-temperature exciton–polaron formation in these DJ structures (Biswas et al., 2023).

The same ligand dependence propagates into hot-carrier cooling. In FPT, which has stronger exciton–phonon coupling and larger reorganization energy, the slow hot-carrier cooling component $n=2$8 increases from 6 ps to 11.5 ps as the excitation density rises from $n=2$9 to $(A^+)_{2}MX_4$0, and the corresponding amplitude increases from 8.6% to 15.8%. In FPP, $(A^+)_{2}MX_4$1 remains near 8.5 ps and nearly independent of fluence. The stated interpretation is a hot-phonon bottleneck: stronger exciton–phonon coupling increases the hot-carrier lifetime at high excitation density (Biswas et al., 2023).

Interlayer carrier transport in DJ halides has also been quantified directly. First-principles NAMD on $(A^+)_{2}MX_4$2 lead-iodide heterostructures found sub-picosecond transfer of both electrons and holes from the $(A^+)_{2}MX_4$3 to the $(A^+)_{2}MX_4$4 slab. For a DJ PDMA system and an RP BA system with similar inorganic–inorganic separation, the DJ phase shows much larger VBM–VBM electron–phonon coupling and correspondingly faster hole transfer, whereas CBM–CBM coupling remains similar. A more electronically active DJ spacer, BAESBT$(A^+)_{2}MX_4$5, places spacer orbitals near both VBM and CBM and enhances both hole and electron transfer despite a 10 Å spacer width; CF$(A^+)_{2}MX_4$6-BAESBT further improves CB alignment and accelerates electron transfer from the beginning of the trajectory (Zheng et al., 2023).

4. Synthesis, phase control, and polaritonic photonics

Synthetic control over DJ thickness remains a central issue because higher-$(A^+)_{2}MX_4$7 phases are harder to access than lower-$(A^+)_{2}MX_4$8 ones. In kinetically controlled space confinement, a fixed 3AMP DJ $(A^+)_{2}MX_4$9 parent solution can be driven toward phase-pure $$(\mathrm{A'})_2\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$0 and $$(\mathrm{A'})_2\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$1 by increasing crystallization temperature or time. The study attributes the higher thresholds for DJ $$(\mathrm{A'})_2\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$2 and $$(\mathrm{A'})_2\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$3, relative to RP analogues, to the smaller interlayer spacing and additional interlayer interaction in DJ phases, which limit precursor diffusion during intercalation. An SVM phase diagram in temperature–time space then defines the regions yielding phase-pure $$(\mathrm{A'})_2\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$4, $$(\mathrm{A'})_2\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$5, and $$(\mathrm{A'})_2\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$6 DJ crystals (2212.00989).

At the microscale, DJ lead-iodide single-crystal microwires have been fabricated by template-confined microfluidic growth. In the reported implementation, PDMS channels 6 µm wide and 300 nm high are filled with 0.35 M precursor solution and allowed to crystallize slowly, yielding millimeter-long DJ microwires with flat surfaces and sharp edges. These structures function as rectangular high-index waveguides and can be integrated with PMMA gratings for Fourier-space out-coupling (Coriolano et al., 2023).

Such microwires support room-temperature waveguide exciton–polaritons. In HE and DMPA(2) DJ microwires, TE-polarized angle-resolved PL shows anti-crossing between guided photonic modes and the exciton resonance, and fitting to a coupled-oscillator Hamiltonian gives $$(\mathrm{A'})_2\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$7 meV for HE and $$(\mathrm{A'})_2\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$8 meV for DMPA(2). The same experiments resolve a long-debated double-peak emission in DJ crystals: the additional low-energy edge-emission peak is assigned not to a separate excitonic transition or defect emission, but to guided hybrid exciton–photon modes that propagate to the edge and scatter out there (Coriolano et al., 2023).

This suggests that DJ perovskites occupy an unusual position among solution-processed semiconductors: slab thickness, organic-spacer geometry, and guided-mode engineering can be varied within one materials platform to co-design exciton energy, waveguide dispersion, and strong-coupling behavior. The experimental record already includes deterministic $$(\mathrm{A'})_2\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$9-control on the crystal-growth side and room-temperature polariton waveguides on the photonics side (2212.00989, Coriolano et al., 2023).

5. Stability, photooxidation, and light-driven phase behavior

DJ phases are frequently described as structurally more stable than RP analogues, but the literature has refined the mechanism. In layered Cu-, Mn-, and Co-based HOIPs, temperature-dependent Raman measurements showed that structural phase transitions below room temperature occurred only in EA-containing RP samples; DJ phases with EDA or PEAA showed no detectable structural phase transitions between 80 and 340 K in the monitored modes (Asensio et al., 2024).

Mixed-halide DJs remain dynamically rich under illumination. In encapsulated $(\mathrm{A'}^{2+})MX_4$0, constant illumination drives photo de-mixing from the pristine phase directly to coexisting I-rich and Br-rich DJ phases, as indicated by isosbestic points in the evolving absorption spectrum. The optical changes are almost fully reversible in the dark, but XRD peak broadening and intensity loss do not recover, pointing to irreversible structural changes such as nanodomain formation. The temperature-dependent kinetics yield an activation energy of approximately 0.94 eV for photo de-mixing, and the extracted photo-miscibility gap widens as temperature decreases (Wang et al., 2021).

The most specific mechanistic distinction between DJ and RP photooxidation has been formulated in terms of spacer deprotonation. Comparative studies across multiple RP and DJ lead iodides found that the superior photooxidation resistance of DJ perovskites cannot be explained by commonly proposed differences in superoxide generation, interlayer distance, or lattice structural rigidity. Instead, RP spacers undergo effective loss after a single deprotonation event, whereas a DJ diammonium spacer remains attached after single deprotonation and requires double deprotonation of the same molecule before the neutral amine can leave. The decreased likelihood of such double deprotonation events suppresses organic-cation vacancy formation, halide migration, and irreversible decomposition, and solar cells capped with DJ layers outperform RP-capped analogues in operational stability (Ren et al., 2024).

Taken together, these results narrow a common misconception. Moisture resistance alone does not capture the DJ stability advantage. The available evidence instead points to a broader operando picture in which absence of a van der Waals gap, altered ion-migration pathways, and especially the double-deprotonation requirement of diammonium spacers govern the superior resistance of DJ perovskites to photooxidative and electrochemically induced degradation (Ren et al., 2024).

6. Magnetism, ferroelectricity, and data-driven design

DJ perovskites are not restricted to lead-halide optoelectronics. In Cu-based layered HOIPs, decreasing interlayer distance along the series PEA$(\mathrm{A'}^{2+})MX_4$1CuCl$(\mathrm{A'}^{2+})MX_4$2 $(\mathrm{A'}^{2+})MX_4$3 EA$(\mathrm{A'}^{2+})MX_4$4CuCl$(\mathrm{A'}^{2+})MX_4$5 $(\mathrm{A'}^{2+})MX_4$6 PEAACuCl$(\mathrm{A'}^{2+})MX_4$7 $(\mathrm{A'}^{2+})MX_4$8 EDACuCl$(\mathrm{A'}^{2+})MX_4$9 drives a crossover from a 2D ferromagnet to quasi-3D antiferromagnetism. In the DJ member EDACuCl$$\mathrm{A'}\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$0, $$\mathrm{A'}\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$1 K, $$\mathrm{A'}\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$2, and the magnetization remains almost linear up to 50 kOe, consistent with strong AFM interlayer coupling. In the Mn DJ EDAMnCl$$\mathrm{A'}\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$3, $$\mathrm{A'}\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$4 K, no spin-canting is detected, and the weaker spin-flop transition is attributed to perfectly aligned neighboring octahedral layers that suppress Dzyaloshinskii–Moriya interactions. By contrast, the Co-based DJ-like EDACoCl$$\mathrm{A'}\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$5 remains essentially paramagnetic (Asensio et al., 2024).

In oxide DJs, layered $$\mathrm{A'}\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$6 niobates provide a distinct functional regime. Dense polycrystalline CsNdNb$$\mathrm{A'}\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$7O$$\mathrm{A'}\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$8 and RbNdNb$$\mathrm{A'}\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$9O$$\mathrm{A'}\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$0 exhibit room-temperature polarization hysteresis loops consistent with ferroelectricity, with remanent polarizations of 2–3 $$\mathrm{A'}\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$1C/cm$$\mathrm{A'}\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$2. The reported mechanism is hybrid improper ferroelectricity induced by the combination of two non-polar octahedral rotations. CsNdNb$$\mathrm{A'}\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$3O$$\mathrm{A'}\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$4 shows a dielectric anomaly at 625 K corresponding to the ferroelectric transition, whereas no dielectric anomaly is observed in RbNdNb$$\mathrm{A'}\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$5O$$\mathrm{A'}\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$6 up to 773 K, consistent with persistence of polar $$\mathrm{A'}\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$7 symmetry to higher temperature (Asaki et al., 2020).

Recent computational workflows have generalized DJ design space far beyond traditional trial-and-error spacer selection. An inverse-design study introduced a 12-digit invertible fingerprint for conjugated diammonium spacers, combined with high-throughput DFT, interpretable ML, and synthesis-feasibility screening; it identified 56 DJ perovskites with targeted Ib, IIa, and IIb energy-level alignments. In parallel, a multiscale screening study covering more than 2,000 RP and DJ 2D perovskites computed band gaps, thermoelectric metrics, and Rashba–Dresselhaus splitting, with BDA MA$$\mathrm{A'}\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$8Pb$$\mathrm{A'}\mathrm{A}_{n-1}\mathrm{B}_n\mathrm{X}_{3n+1}$$9I$n=1$00 reported at $n=1$01 (Lyu et al., 30 Sep 2025, Stanton et al., 17 May 2025).

Device-level modeling has also started to incorporate DJ-specific architectures directly. SCAPS-1D simulations of a 2D/absorber/2D stack using DJ phases as both transport layers reported peak efficiencies of 41.00% for Sb$n=1$02Se$n=1$03 and 41.19% for CZTSSe in $n=1$04 structures. A plausible implication is that DJ perovskites are becoming not only active absorbers and capping layers but also a modular interface platform for transport, passivation, and band-alignment control in heterogeneous devices (Hasan et al., 18 Aug 2025).