Photoinduced Halide Segregation in Ruddlesden-Popper 2D Mixed Halide Perovskite Films

Elucidation of the suppression of photoinduced segregation in 2D mixed halide, A2PbI2Br2: Critical role of A2PbBr4 photostability

2D lead halide perovskites are used to improve device operational stability due to increased environmental stability and reduced ion migration compared to 3D perovskites. However, the relationship between the 2D perovskite stability under illumination and spacer cation is still not well understood. Thus, we examine photoinduced halide segregation (PHS) in different 2D mixed-halide perovskites and show that PHS is suppressed in the materials which have photostable bromide halide phase. As the spacer cations provide the barrier to ion migration in 2D perovskites, PHS would be facilitated by the loss of spacer cations through their interactions with various mobile oxidized halide species, resulting in organic ammonium deprotonation and spacer cation vacancy formation. The existence of a photostable A2PbBr4 phase, which does not exhibit spacer cation loss, results in the suppression of PHS in 2D mixed halide perovskites due to reduced spacer vacancy formation and consequently reduced halide ion migration under illumination.

Stretchable Primary-Blue Color-Conversion Layer: In Situ Crystallization of Phase-Engineered Perovskite Nanocrystals in an Organic Matrix

Although the use of ultraviolet (UV) light-emitting diode backlight with red, green, and blue color-conversion layers (CCLs) in displays simplifies the manufacturing process and improves display uniformity, research on blue CCLs remains limited and has been mostly reported in the sky-blue region (> 470 nm), which is insufficient to satisfy the Rec. 2020 color standard. As halide perovskites offer a high extinction coefficient, color purity, and photoluminescence quantum yield (PLQY), they become highly competitive color-converting materials for CCLs. This work presents a simple method for the in situ fabrication of perovskite nanocrystal (NC) films for primary-blue CCL and additionally proposes a set of scientific guidance rules regarding significant factors that affect the nucleation and in situ crystallization kinetics of perovskite NCs. The fabricated films are highly stretchable, emit bright primary-blue light (∼460 nm), and have PL that is tolerant to UV irradiation. By introducing fluorinated arylammonium salts, the quantum and dielectric confinement effects are desirably adjusted, which induces efficient energy transfer processes for primary-blue emission. This strategy yields phase-engineered perovskite NCs embedded in an organic matrix, which enables spectrally stable and robust PL under high tensile strain (> 250%) and after prolonged UV irradiation (> 40 d). Consequently, this work demonstrates that the in situ fabricated stretchable blue CCLs achieve 100% agreement with Rec. 2020.

Halide-Diffusion-Assisted Perovskite Lamination Process for Semitransparent Perovskite Solar Cells

Semitransparent perovskite solar cells (PSCs) efficiently absorb light from both front and rear sides under illumination, and hence, PSCs have the potential for use in applications requiring bifacial or tandem solar cells. A facile method to fabricate semitransparent PSCs involves preparing a perovskite (PVSK) film on two transparent substrates and then laminating the substrates together. However, realizing high-performance laminated semitransparent PSCs is challenging because the imperfect contact at the PVSK interlayer results in void formation and partial degradation of PVSK. To address this issue, a halide-diffusion-assisted lamination (HDL) method is proposed. In the method, a controlled halide concentration gradient is used to effectively laminate the top and bottom PVSK layers. Semitransparent PSCs prepared through the HDL method (hereafter referred to as HDL-PSCs) exhibited a power conversion efficiency (PCE) of 18.93%. In particular, an HDL-PSC exhibited higher thermal stability, maintaining its initial PCE for over 1200 h at 85 °C.

Why Mixed Halides in 2D Chiral Perovskites Weaken Chirality-Induced Spin Selectivity

2D Ruddlesden-Popper (RP) perovskites, upon inclusion of a chiral amine, exhibit chirality-induced spin selectivity (CISS). Although alloying at the halogen site in MBA-based RPs (MBA: methylbenzylammonium) is one of the suitable routes to tune the CISS effect, the mixed-halide RP perovskites exhibited complete suppression of chirality when probed through circular dichroism (CD). Here, we present the CISS effect in a series of mixed-halide RP perovskites. We show that photoinduced halide segregation is the origin for the apparent chirality suppression. The spin-dependent charge transport was evidenced through magnetic-conducting atomic force microscopy (mc-AFM) studies and magnetoresistance (MR) measurements. The mc-AFM results show that in (R/S-MBA)2PbI4(1-x)Br4x, the CISS effect decreases with bromide inclusion, nonmonotonically; the microstrain developed in the lattice and the spin-polarized charge transport are found to be correlated. Such a behavior has been explained through an inhomogeneity in the strength of the hydrogen bond between the organic moieties and halogens in the inorganic framework of the compounds. Our results further inferred that the hydrogen-bond-induced coupling transfers the chirality from the amine to the inorganic sublattice. The work explains the weakened CISS effect in mixed-halide chiral RP perovskites and provides a strategy to tune the spin-polarized charge transport as well.

Free Charge Carrier Generation by Visible-Light-Absorbing Organic Spacers in Ruddlesden-Popper Layered Perovskites

Incorporating organic semiconductor building blocks as spacer cations into layered hybrid perovskites provides an opportunity to develop new materials with novel optoelectronic properties, including nanoheterojunctions that afford spatial separation of electron and hole transport. However, identifying organics with suitable structure and electronic energy levels to selectively absorb visible light has been a challenge in the field. In this work, we introduce a new lead-halide-based Ruddlesden-Popper perovskite structure based on a visible-light-absorbing naphthalene-iminoimide cation (NDI-DAE). Thin films of (NDI-DAE)2PbI4 show a quenched photoluminescence and transient absorption dynamics consistent with the formation of a charge transfer state or free charge carriers when either the inorganic or organic layer is photoexcited, suggesting the formation of a type II nanoheterostructure. Time-resolved microwave conductivity analysis supports free charge generation with sum mobilities up to 4 × 10-4 cm2 V-1 s-1. Mixed halide (NDI-DAE)2Pb(IxBr1-x)4 films show modified inorganic layer band gaps and a photoluminescent reversed type I nanoheterostructure with high bromide content (e.g., for x = 0). At x = 0.5, transient absorption and microwave conductivity measurements provide strong evidence that selective visible-light absorbance by the NDI-DAE cation generates separated free carriers via hole transfer to the inorganic layer (leaving photogenerated electrons in the organic layer), which represents an important step toward enhancing light harvesting and affording the spatial separation of charge carrier transport in stable layered perovskite-based devices.

Positive and Negative Effects under Light Illumination in Halide Perovskites

Metal halide perovskites (MHPs) have excellent characteristics and present great potential in a broad range of applications such as solar cells, light-emitting diodes, and photodetectors. However, the light stability of devices remains an unresolved issue and has received great research attention. Under light illumination, MHPs exhibit various anomalous phenomena, such as photoluminescence (PL) enhancement, defect curing, PL blinking, and phase segregation. These phenomena are commonly considered intimately correlated with the performance and stability of MHP devices. In recent years, significant efforts have been made experimentally and theoretically toward understanding the physical origins of these anomalous effects. However, most research focuses on negative effects while the positive effects are mostly ignored. Herein, the positive effects and the negative effects of light soaking in MHPs are systematically discussed with a classification of the correlated physical mechanisms by specifically focusing on variation occurring in timescale from second to hour, corresponding to the unique ionic-electronic interaction. This intends to provide a new insight into ion effects on excellent properties of perovskites, and deep physical understanding of charge-carrier and ion dynamics in perovskite, and theoretical guidelines for the fabrication of high-quality and stability perovskite-based photovoltaic and photoelectric devices.

New Nanophotonics Approaches for Enhancing the Efficiency and Stability of Perovskite Solar Cells

Over the past decade, the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has experienced a remarkable ascent, soaring from 3.8% in 2009 to a remarkable record of 26.1% in 2023. Many recent approaches for improving PSC performance employ nanophotonic technologies, from light harvesting and thermal management to the manipulation of charge carrier dynamics. Plasmonic nanoparticles and arrayed dielectric nanostructures have been applied to tailor the light absorption, scattering, and conversion, as well as the heat dissipation within PSCs to improve their PCE and operational stability. In this review, it is begin with a concise introduction to define the realm of nanophotonics by focusing on the nanoscale interactions between light and surface plasmons or dielectric photonic structures. Prevailing strategies that utilize resonance-enhanced light-matter interactions for boosting the PCE and stability of PSCs from light trapping, carrier transportation, and thermal management perspectives are then elaborated, and the resultant practical applications, such as semitransparent photovoltaics, colored PSCs, and smart perovskite windows are discussed. Finally, the state-of-the-art nanophotonic paradigms in PSCs are reviewed, and the benefits of these approaches in improving the aesthetic effects and energy-saving character of PSC-integrated buildings are highlighted.

Axial-Equatorial Halide Ordering in Layered Hybrid Perovskites from Isotropic-Anisotropic 207 Pb NMR

Bandgap-tuneable mixed-halide 3D perovskites are of interest for multi-junction solar cells, but suffer from photoinduced spatial halide segregation. Mixed-halide 2D perovskites are more resistant to halide segregation and are promising coatings for 3D perovskite solar cells. The properties of mixed-halide compositions depend on the local halide distribution, which is challenging to study at the level of single octahedra. In particular, it has been suggested that there is a preference for occupation of the distinct axial and equatorial halide sites in mixed-halide 2D perovskites. 207 Pb NMR can be used to probe the atomic-scale structure of lead-halide materials, but although the isotropic 207 Pb shift is sensitive to halide stoichiometry, it cannot distinguish configurational isomers. Here, we use 2D isotropic-anisotropic correlation 207 Pb NMR and relativistic DFT calculations to distinguish the [PbX6 ] configurations in mixed iodide-bromide 3D FAPb(Br1-x Ix )3 perovskites and 2D BA2 Pb(Br1-x Ix )4 perovskites based on formamidinium (FA+ ) and butylammonium (BA+ ), respectively. We find that iodide preferentially occupies the axial site in BA-based 2D perovskites, which may explain the suppressed halide mobility.

Halide Ordering Enables Superior Charge Transport in 3D (NMPDA)Pb2 I4 Br2 Perovskitoid Single Crystal

Halide composition engineering has been demonstrated as an effective strategy for optical and electronic properties modulation in 3D perovskites. While the impact of halide mixing on the structural and charge transport properties of 3D perovskitoids remains largely unexplored. Herein, it is demonstrated that bromine (Br) mixing in 3D (NMPDA)Pb2 I6 (NMPDA = N-methyl-1,3-propane diammonium) perovskitoid yields stabilized (NMPDA)Pb2 I4 Br2 with specific ordered halide sites, where Br ions locate at the edge-sharing sites. The halide ordered structure enables stronger H-bonds, shorter interlayer distance, and lower octahedra distortion in (NMPDA)Pb2 I4 Br2 with respect to the pristine (NMPDA)Pb2 I6 . These attributes further result in high ion migration activation energy, low defect states density, and enhanced carrier mobility-lifetime product (µτ), as underpinned by the electrical properties investigation and DFT calculations. Remarkably, the parallel configured photodetector based on (NMPDA)Pb2 I4 Br2 single crystal delivers a high on/off current ratio of 3.92 × 103 , a satisfying photoresponsivity and detectivity of 0.28 A W-1 and 3.05 × 1012 Jones under 10.94 µW cm-2 irradiation, superior to that of (NMPDA)Pb2 I6 and the reported 3D perovskitoids. This work sheds novel insight on exploring 3D mixed halide perovskitoids toward advanced and stable optoelectronic devices.

Ion Migration in Lead-Halide Perovskites: Cation Matters

Metal halide perovskites exhibit remarkable properties for optoelectronic applications, yet their susceptibility to ion migration poses challenges for device stability. Previous research has predominantly focused on the migration of the halide ions. However, the migration of cations, which also has a significant influence on the device performance, is largely overlooked. In this Perspective, we review the migration of cations and their impacts on perovskite materials and devices. Special attention shall be devoted to recent insights into the migration of L-site organic cations in 2D/3D perovskites. We outline inspirations and directions for further research into the cation migration of perovskites, highlighting new possibilities in advancing perovskite optoelectronics.

Halide Ion Mixing across Colloidal 2D Ruddlesden-Popper Perovskites: Implication of Spacer Ligand on Mixing Kinetics

Halide ion exchange seen in metal halide perovskites provide a substantial opportunity to control their halide composition and corresponding optoelectronic properties. Halide ion mixing across colloidal 3D perovskite nanocrystals have been extensively studied while the mixing within colloidal 2D counterparts remain underexplored. In this study, the halide ion exchange kinetics across colloidally stable 2D Ruddlesden-Popper layered bromide (Br) and iodide (I) perovskites using two different spacer ligands such as aromatic phenethylammonium (PEA) versus linear butyammonium (BA) is demonstrated. The halide exchange kinetic rate constant (k), as determined by tracking time-dependent absorbance changes, indicates that Br/I halide mixing in 2D PEA-based perovskites (2.7 × 10-3 min-1 ) occurs at an order of magnitude slower than in 2D BA-based perovskites (3.3 × 10-2 min-1 ). Concentration (≈1 mM to 100 mM) and temperature-dependent (50 to 80 °C) kinetic studies further allow for the determination of activation barrier for halide ion mixing across the 2D layered perovskites with 75.2 ± 4.4 kJ mol-1 (2D PEA) and 57.8 ± 7.8 kJ mol-1 (2D BA), respectively. The activation energy reveals that the type of spacer cations plays a crucial role in controlling the halide ion mobility and halide stability due mainly to the internal ligand chemical interaction within 2D structures.

Inhibition of Ion Migration for Highly Efficient and Stable Perovskite Solar Cells

In recent years, organic-inorganic halide perovskites are now emerging as the most attractive alternatives for next-generation photovoltaic devices, due to their excellent optoelectronic characteristics and low manufacturing cost. However, the resultant perovskite solar cells (PVSCs) are intrinsically unstable owing to ion migration, which severely impedes performance enhancement, even with device encapsulation. There is no doubt that the investigation of ion migration and the summarization of recent advances in inhibition strategies are necessary to develop "state-of-the-art" PVSCs with high intrinsic stability for accelerated commercialization. This review systematically elaborates on the generation and fundamental mechanisms of ion migration in PVSCs, the impact of ion migration on hysteresis, phase segregation, and operational stability, and the characterizations for ion migration in PVSCs. Then, many related works on the strategies for inhibiting ion migration toward highly efficient and stable PVSCs are summarized. Finally, the perspectives on the current obstacles and prospective strategies for inhibition of ion migration in PVSCs to boost operational stability and meet all of the requirements for commercialization success are summarized.

Synergy of 3D and 2D Perovskites for Durable, Efficient Solar Cells and Beyond

Three-dimensional (3D) organic-inorganic lead halide perovskites have emerged in the past few years as a promising material for low-cost, high-efficiency optoelectronic devices. Spurred by this recent interest, several subclasses of halide perovskites such as two-dimensional (2D) halide perovskites have begun to play a significant role in advancing the fundamental understanding of the structural, chemical, and physical properties of halide perovskites, which are technologically relevant. While the chemistry of these 2D materials is similar to that of the 3D halide perovskites, their layered structure with a hybrid organic-inorganic interface induces new emergent properties that can significantly or sometimes subtly be important. Synergistic properties can be realized in systems that combine different materials exhibiting different dimensionalities by exploiting their intrinsic compatibility. In many cases, the weaknesses of each material can be alleviated in heteroarchitectures. For example, 3D-2D halide perovskites can demonstrate novel behavior that neither material would be capable of separately. This review describes how the structural differences between 3D halide perovskites and 2D halide perovskites give rise to their disparate materials properties, discusses strategies for realizing mixed-dimensional systems of various architectures through solution-processing techniques, and presents a comprehensive outlook for the use of 3D-2D systems in solar cells. Finally, we investigate applications of 3D-2D systems beyond photovoltaics and offer our perspective on mixed-dimensional perovskite systems as semiconductor materials with unrivaled tunability, efficiency, and technologically relevant durability.

Fabrication and Characterization of 2D Layered Perovskites with a Gradient Band Gap

Vertical gradient band-gap heterostructures of two-dimensional (2D) layered perovskites have attracted considerable research interest due to their superior optoelectronic properties and demonstrated potential for use in optical devices. However, its fabrication has been challenging. In this investigation, 2D Ruddlesden-Popper mixed halide perovskite single crystals with a vertical gradient band gap were synthesized by using a solid-state halide diffusion process. X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements after diffusion confirm that the crystalline and morphology remain intact. The transmittance and photoluminescence (PL) spectra show the formation of a vertical gradient band gap that is ascribed to gradient halide distribution through halide intermixing. The mixed halide crystal exhibits high stability with completely suppressed phase segregation in the time-dependent PL measurement. The time-resolved photoluminescence (TRPL) spectra prove that the mixed halide sample has an enhanced carrier transport due to the Förster resonance energy transfer (FRET) effect. Besides, the halide diffusion behavior is found to be different from the previously proposed "layer-by-layer" diffusion model in exfoliated crystals. The gradient band-gap structure is critical for various applications in which vertical carrier transport is demanded.

Two-Dimensional Metal Halides for X-Ray Detection Applications

Metal halide perovskites have recently emerged as promising candidates for the next generation of X-ray detectors due to their excellent optoelectronic properties. Especially, two-dimensional (2D) perovskites afford many distinct properties, including remarkable structural diversity, high generation energy, and balanced large exciton binding energy. With the advantages of 2D materials and perovskites, it successfully reduces the decomposition and phase transition of perovskite and effectively suppresses ion migration. Meanwhile, the existence of a high hydrophobic spacer can block water molecules, thus making 2D perovskite obtain excellent stability. All of these advantages have attracted much attention in the field of X-ray detection. This review introduces the classification of 2D halide perovskites, summarizes the synthesis technology and performance characteristics of 2D perovskite X-ray direct detector, and briefly discusses the application of 2D perovskite in scintillators. Finally, this review also emphasizes the key challenges faced by 2D perovskite X-ray detectors in practical application and presents our views on its future development.

Controlling Phase Transitions in Two-Dimensional Perovskites through Organic Cation Alloying

We demonstrate control over the phase transition temperature of Ruddlesden-Popper two-dimensional (2D) perovskites by alloying alkyl organic cations of varying lengths. By blending hexylammonium with pentylammonium or heptylammonium cations in different ratios, we continuously tune the phase transition temperature of 2D perovskites from approximately 40 to -80 °C in both crystalline powders and thin films. Correlating temperature-dependent grazing incidence wide-angle X-ray scattering and photoluminescence spectroscopy, we also demonstrate that the phase transition in the organic layer couples to the inorganic lattice, impacting PL intensity and wavelength. We take advantage of changes in PL intensity to image the dynamics of this phase transition and show asymmetric phase growth at the microscale. Our findings provide the necessary design principles to precisely control phase transitions in 2D perovskites for applications such as solid-solid phase change materials and barocaloric cooling.

Light-Induced Halide Segregation in 2D and Quasi-2D Mixed-Halide Perovskites

Photoinduced halide segregation hinders widespread application of three-dimensional (3D) mixed-halide perovskites. Much less is known about this phenomenon in lower-dimensional systems. Here, we study photoinduced halide segregation in lower-dimensional mixed iodide-bromide perovskites (PEA2MA n-1Pb n (Br x I1-x )3n+1, with PEA+: phenethylammonium and MA+: methylammonium) through time-dependent photoluminescence (PL) spectroscopy. We show that layered two-dimensional (2D) structures render additional stability against the demixing of halide phases under illumination. We ascribe this behavior to reduced halide mobility due to the intrinsic heterogeneity of 2D mixed-halide perovskites, which we demonstrate via 207Pb solid-state NMR. However, the dimensionality of the 2D phase is critical in regulating photostability. By tracking the PL of multidimensional perovskite films under illumination, we find that while halide segregation is largely inhibited in 2D perovskites (n = 1), it is not suppressed in quasi-2D phases (n = 2), which display a behavior intermediate between 2D and 3D and a peculiar absence of halide redistribution in the dark that is only induced at higher temperature for the quasi-2D phase.

Thermodynamic Origin of the Photostability of the Two-Dimensional Perovskite PEA2Pb(I1-x Br x )4

The two-dimensional (2D) mixed halide perovskite PEA₂Pb(I_1-x Br _x )₄ exhibits high phase stability under illumination as compared to the three-dimensional (3D) counterpart MAPb(I_1-x Br _x )₃. We explain this difference using a thermodynamic theory that considers the sum of a compositional and a photocarrier free energy. Ab initio calculations show that the improved compositional phase stability of the 2D perovskite is caused by a preferred I-Br distribution, leading to a much lower critical temperature for halide segregation in the dark than for the 3D perovskite. Moreover, a smaller increase of the band gap with Br concentration x and a markedly shorter photocarrier lifetime in the 2D perovskite reduce the driving force for phase segregation under illumination, enhancing the photostability.

Are Mixed-Halide Ruddlesden-Popper Perovskites Really Mixed?

Mixing bromine and iodine within lead halide perovskites is a common strategy to tune their optical properties. This comes at the cost of instability, as illumination induces halide segregation and degrades device performances. Hence, understanding the behavior of mixed-halide perovskites is crucial for applications. In 3D perovskites such as MAPb(Br _x I_1-x )₃ (MA = methylammonium), all of the halide crystallographic sites are similar, and the consensus is that bromine and iodine are homogeneously distributed prior to illumination. By analogy, it is often assumed that Ruddlesden-Popper layered perovskites such as (BA)₂MAPb₂(Br _x I_1-x )₇ (BA = butylammonium) behave alike. However, these materials possess a much wider variety of halide sites featuring diverse coordination environments, which might be preferentially occupied by either bromine or iodine. This leaves an open question: are mixed-halide Ruddlesden-Popper perovskites really mixed? By combining powder and single-crystal diffraction experiments, we demonstrate that this is not the case: bromine and iodine in RP perovskites preferentially occupy different sites, regardless of the crystallization speed.

Tuning the optical properties of 2D monolayer silver-bismuth bromide double perovskite by halide substitution

Silver-bismuth double perovskites are promising replacement materials for lead-based ones in photovoltaic (PV) devices due to the lower toxicity and enhanced stability to environmental factors. In addition, they might even be more suitable for indoor PV, due to the size of their bandgap better matching white LEDs emission. Unfortunately, their optoelectronic performance does not reach that of the lead-based counterparts, because of the indirect nature of the band gap and the high exciton binding energy. One strategy to improve the electronic properties is the dimensional reduction from the 3D to the 2D perovskite structure, which features a direct band gap, as it has been reported for 2D monolayer derivates of Cs₂AgBiBr₆obtained by substituting Cs⁺cations with bulky alkylammonium cations. However, a similar dimensional reduction also brings to a band gap opening, limiting light absorption in the visible. In this work, we report on the achievement of a bathochromic shift in the absorption features of a butylammonium-based silver-bismuth bromide monolayer double perovskite through doping with iodide and study the optical properties and stability of the resulting thin films in environmental conditions. These species might constitute the starting point to design future sustainable materials to implement as active components in indoor photovoltaic devices used to power the IoT.

Halide Mixing Inhibits Exciton Transport in Two-dimensional Perovskites Despite Phase Purity

Halide mixing is one of the most powerful techniques to tune the optical bandgap of metal-halide perovskites. However, halide mixing has commonly been observed to result in phase segregation, which reduces excited-state transport and limits device performance. While the current emphasis lies on the development of strategies to prevent phase segregation, it remains unclear how halide mixing may affect excited-state transport even if phase purity is maintained. Here, we study exciton transport in phase pure mixed-halide 2D perovskites of (PEA)2Pb(I1-x Br x )4. Using transient photoluminescence microscopy, we show that, despite phase purity, halide mixing inhibits exciton transport. We find a significant reduction even for relatively low alloying concentrations. By performing Brownian dynamics simulations, we are able to reproduce our experimental results and attribute the decrease in diffusivity to the energetically disordered potential landscape that arises due to the intrinsic random distribution of alloying sites.

Two-Dimensional Halide Perovskites: Approaches to Improve Optoelectronic Properties

Three-dimensional (3D) halide perovskites (HPs) are in the spotlight of materials science research due to their excellent photonic and electronic properties suitable for functional device applications. However, the intrinsic instability of these materials stands as a hurdle in the way to their commercialization. Recently, two-dimensional (2D) HPs have emerged as an alternative to 3D perovskites, thanks to their excellent stability and tunable optoelectronic properties. Unlike 3D HPs, a library of 2D perovskites could be prepared by utilizing the unlimited number of organic cations since their formation is not within the boundary of the Goldschmidt tolerance factor. These materials have already proved their potential for applications such as solar cells, light-emitting diodes, transistors, photodetectors, photocatalysis, etc. However, poor charge carrier separation and transport efficiencies of 2D HPs are the bottlenecks resulting in inferior device performances compared to their 3D analogs. This minireview focuses on how to address these issues through the adoption of different strategies and improve the optoelectronic properties of 2D perovskites.