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Low-dimensional metal halide perovskites have emerged as promising alternatives to the traditional three-dimensional (3D) components, due to their greater structural tunability and environmental stability. Dion-Jacobson (DJ) phase two-dimensional (2D) perovskites, which are formed by incorporating bulky organic diammonium cations into inorganic frameworks that comprises a symmetrically layered array, have recently attracted increasing research interest. The structure-property characteristics of DJ phase perovskites endow them with a unique combination of photovoltaic efficiency and stability, which has led to their impressive employment in perovskite solar cells (PSCs). Here, we review the achievements that have been made to date in the exploitation of DJ phase perovskites in photovoltaic applications. We summarize the various ligand designs, optimization strategies and applications of DJ phase PSCs, and examine the current understanding of the mechanisms underlying their functional behavior. Finally, we discuss the remaining bottlenecks and future outlook for these promising materials, and possible development directions of further commercial processes.

The exceptional photophysical and electronic properties of 2D hybrid perovskites possess potential applications in the field of solar energy harvesting. The present work focuses on the two systems, exhibiting the Dion–Jacobson phase of 2D perovskite consisting of methylammonium (MA) and formamidinium (FA) cations at A‐site and 3‐(aminomethyl)pyridinium (3AMPY) as ring‐shaped organic spacer. Altering A‐site cations creates a distortion of inorganic layers and hydrogen bond interactions. It has been noted that the angles of Pb–I–Pb and I–Pb–I are more symmetric (close to 180°) for (3AMPY)(MA)Pb2I7 compared to (3AMPY)(FA)Pb2I7 and result in increase of bandgap from 1.51 to 1.58 eV. This further leads to a significant difference in Rashba splitting energy under the influence of spin‐orbit coupling effects, where the highest splitting (36 meV) is calculated for conduction band edge of the (3AMPY)(FA)Pb2I7, suggesting the promising applications toward spintronics. The calculated absorption spectra cover the range from 300 to 450 nm, indicating significant optical activity of 2D (3AMPY)(MA)Pb2I7 and (3AMPY)(FA)Pb2I7 in the visible and ultraviolet regions, which bodes well for their application in advanced optoelectronic devices. The bandgap and high absorption coefficients present more than 30% of theoretical power conversion efficiency for both systems, as calculated from the spectroscopic‐limited maximum efficiency. While investigating the influence of A‐site cation variations in Dion–Jacobson phase 2D perovskites (3‐(aminomethyl)pyridinium)(methylammonium)Pb2I7 and (3‐(aminomethyl)pyridinium)(formamidinium)Pb2I7, significant changes in electronic properties are observed. This includes bandgap modifications from 1.51 to 1.58 eV, distinct Rashba splitting effects, and pronounced optical activity, paving the way for high‐efficiency solar energy applications.

Metal halide perovskites (MHPs) show tremendous potential for field‐effect transistors (FETs), but N‐type Pbbased MHP FETs have been hindered by critical challenges, including high defect densities, ion migration, and poor reproducibility. In this work, a simple yet powerful ultrathin TiO2 interlayer strategy is introduced that fundamentally transforms the fabrication of Pb‐based MHP FETs. By pre‐depositing an ultrathin TiO2 layer before perovskite film deposition, reproducible and operationally stable MAPbI3 FETs with remarkable performance are achieved. Comprehensive characterizations reveal that the TiO2 interlayer enhances precursor wetting, promotes larger and more uniform grain formation, reduces defect density, and effectively suppresses non‐radiative recombination and ion migration. The universality of this approach is demonstrated by successfully extending it to 2D Dion‐Jacobson phase perovskites, including PDAPbI4 and its derivatives. The fabricated devices exhibit excellent electrical characteristics, including high on/off ratios, low hysteresis, and impressive stability. As a proof of concept, a complementary inverter is constructed using perovskite‐only components, showcasing the potential for integrated logic circuits. This work provides a robust fabrication method for high‐performance Pb‐based perovskite FETs with broad applicability. An ultrathin TiO2 interlayer strategy is developed for fabricating high‐performance, lead‐based, N‐type perovskite field‐effect transistors. This method improves film quality, reduces defects, and suppresses ion migration, enabling reproducible and stable devices. The strategy is successfully applied to both 3D (MAPbI3) and 2D Dion‐Jacobson phase perovskites, demonstrating its broad applicability and paving the way for perovskite‐based circuits.

The photocatalytic activity of layered perovskite-like oxides in water splitting reaction is dependent on the hydration level and species located in the interlayer slab: simple or complex cations as well as hydrogen-bonded or non-hydrogen-bonded H2O. To study proton localization and dynamics in the HCa2Nb3O10·yH2O photocatalyst with different hydration levels (hydrated—α-form, dehydrated—γ-form, and intermediate—β-form), complementary Nuclear Magnetic Resonance (NMR) techniques were applied. 1H Magic Angle Spinning NMR evidences the presence of different proton containing species in the interlayer slab depending on the hydration level. For α-form, HCa2Nb3O10·1.6H2O, 1H MAS NMR spectra reveal H3O+. Its molecular motion parameters were determined from 1H spin-lattice relaxation time in the rotating frame (T1ρ) using the Kohlrausch-Williams-Watts (KWW) correlation function with stretching exponent β = 0.28: Ea=0.2102 eV, τ0=9.01 × 10−12 s. For the β-form, HCa2Nb3O10·0.8H2O, the only 1H NMR line is the result of an exchange between lattice and non-hydrogen-bonded water protons. T1ρ(1/T) indicates the presence of two characteristic points (224 and 176 K), at which proton dynamics change. The γ-form, HCa2Nb3O10·0.1H2O, contains bulk water and interlayer H+ in regular sites. 1H NMR spectra suggest two inequivalent cation positions. The parameters of the proton motion, found within the KWW model, are as follows: Ea=0.2178 eV, τ0=8.29 × 10−10 s.

In recent years, two-dimensional (2D) layered perovskites, have aroused considerable research interest due to their structural tunability and more stability compared to their 3D counterparts. The presence of long-chain organic cations strongly increases the stability of 2D perovskites. The electronic and optical properties of materials, as important parameters, can significantly affect the function of optoelectronic devices. In this paper, the electronic and optical properties of two-dimensional (2D) layered perovskite materials were studied due to their growing application in optoelectronic devices. The band structure, exciton binding energy, dielectric function, optical conductivity, absorption, and reflection spectra of a 2D (OCA) (MA) n−1 Pb n Br 3n+1 (n = 1, 2, 3) perovskite with Dion–Jacobson structure compared with (BA) 2 (MA) n−1 Pb n Br 3n+1 (n = 1, 2, 3) with Ruddlesden–Popper structure were calculated by density functional theory (DFT) method. We observed that by increasing the number of inorganic sheets, n, the band gap, carrier effective mass, and exciton binding energy of both structures decrease and reach the value of 3D perovskite almost for n = 3 due to quantum confinement effects. The obtained results indicate that the 2D (OCA) with DJ structure has a suitable band gap, high exciton binding energy, and good high absorption in comparison to that of the 2D (BA) with RP structure. DFT calculations can help to get more insight into the experimental findings. These results can be implemented for designing and developing new 2D materials for optoelectronic devices.

HighlightsSoluble compounds are added to the Dion–Jacobson (DJ) perovskite precursor solutions.Current studies and development trends of additive compounds in DJ-phase perovskite solar cells are reviewed.The innate functions of additive compounds in DJ-phase perovskite solar cells are developed.An insightful perspective is outlined for future research in additive compounds for DJ-phase perovskite solar cells.Because of their better chemical stability and fascinating anisotropic characteristics, Dion–Jacobson (DJ)-layered halide perovskites, which owe crystallographic two-dimensional structures, have fascinated growing attention for solar devices. DJ-layered halide perovskites have special structural and photoelectronic features that allow the van der Waals gap to be eliminated or reduced. DJ-layered halide perovskites have improved photophysical characteristics, resulting in improved photovoltaic performance. Nevertheless, owing to the nature of the solution procedure and the fast crystal development of DJ perovskite thin layers, the precursor compositions and processing circumstances can cause a variety of defects to occur. The application of additives can impact DJ perovskite crystallization and film generation, trap passivation in the bulk and/or at the surface, interface structure, and energetic tuning. This study discusses recent developments in additive engineering for DJ multilayer halide perovskite film production. Several additive-assisted bulk and interface optimization methodologies are summarized. Lastly, an overview of research developments in additive engineering in the production of DJ-layered halide perovskite solar cells is offered.

The noteworthy stability of Dion–Jacobson (DJ) phase two-dimensional perovskites marks them as potential contenders for use in optoelectronic applications. Nonetheless, their proliferation is considerably stymied by the constrained charge transport properties inherent to them. This bottleneck is adeptly navigated by deploying 2D-DJ perovskite top layers, seamlessly integrated on 3D perovskite films. We unveil a novel organic cation salt, 4-(Aminomethyl)piperidine (4AMP), as a potent facilitator for treating perovskite photovoltaic films. By employing the annealing technique, we facilitated the in situ creation of a hybrid 2D/3D architecture. Contrasted with conventional 3D architectures, the delineated perovskite heterojunctions with a 2D/3D structure exhibit superior enhanced charge separation, and mitigate photovoltaic losses by proficiently passivating intrinsic defects. The size-graded perovskite 2D/3D structure engineered herein significantly elevates the charge transfer performance, concurrently attenuating the excess lead iodide induced by bulk defects. This precise method resulted in a significant increase in Power Conversion Efficiency, reaching 23.08%, along with an open-circuit voltage (Voc) of 1.17 V. Remarkably, the unpackaged modified device robustly retains 92% of its initial PCE post a 3000 h sojourn under ambient conditions. This discourse propounds a novel paradigm for constructing stable planar PSC 2D/3D heterojunctions, thereby enriching the blueprint for advanced perovskite-based photovoltaic systems.

Many phases related to the perovskite structure are modular in nature, being built from slabs of a parent perovskite interleaved with other structures. These phases are able to accommodate composition change by changing the thickness of the perovskite units or the inter‐slab species. This chapter summarises the structural relationships between four important series, excluding the superconducting cuprates. The Aurivillius phases contain slabs of perovskite sliced along the ideal [100]direction. They are formed by replacement of the interlayer A 2 structures in the Ruddlesden‐Popper phases and A' in the Dion‐Jacobson phases with a layer of composition Bi 2 O 2 . Structures are often given similar but different space groups, and in some cases it is deemed best to described the structures as incommensurate modulated forms. The phases related to Ca 2 Nb 2 O 7 are built from slabs of the perovskite structure, this time cut into slabs parallel to ideal perovskite [110] p planes.

Two‐dimensional (2D) lead halide perovskites (LHPs) have captured a range of interest for the advancement of state‐of‐the‐art optoelectronic devices, highly efficient solar cells, next‐generation energy harvesting technologies owing to their hydrophobic nature, layered configuration, and remarkable chemical/environmental stabilities. These 2D LHPs have been categorized into the Dion‐Jacobson (DJ) and Ruddlesden‐Popper (RP) systems based on their layered configuration respectively. To efficiently classify the RP and DJ phases synthetically and reduce reliance on trial/error method, machine learning (ML) techniques needs to develop. Herein, this work effectively identifies RP and DJ phases of 2D LHPs by implementing various ML models. ML models were trained on 264 experimental data set using 10‐fold stratified cross‐validation, hyperparameter optimization with Optuna, and Shapley Additive Explanations (SHAP) were employed. The stacking classifier efficiently classified RP and DJ phases, demonstrating a minimal variation between the sensitivity and specificity and achieved a high Balance Accuracy (BA) of (0.83) on independent test data set. Our best model tested on 17 hybrid 2D LHPs and three experimental synthesized 2D LHPs aligns well experimental outcomes, a significant advance in cutting edge ML models. Thus, this proposed study has unlocked a new route toward the rational classification of RP and DJ phases of 2D LHPs. Optimized ML framework for predicting RP and Dj phases in perovskite solar cells.