2D Perovskite Films Research Articles

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The key to further improve 2D/3D perovskite solar cells is to passivate the defects of 3D perovskite layer and enhance the poor charge transport ability of 2D perovskite film. In the article EOM2‐2021‐0036, Chen and Jin added multifunctional CNT:TiO2 into 3D perovskite layer to effectively passivate the defects of the 3D perovskite layer and improve the charge mobility of the 3D layer as well as enhance the conductivity of 2D perovskite layer, which significantly improves the the device performance. This provides a reference for the development of 2D/3D perovskite solar cells.image

Film formation mechanisms in mixed-dimensional 2D/3D halide perovskite films revealed by in situ grazing-incidence wide-angle X-ray scattering

<h2>Summary</h2> Mixed-dimensional 2D/3D hybrid halide perovskites retain the stability of 2D perovskites (formula (A′)2(A)_n−1Pb_nI_3n+1) and long diffusion lengths of the 3D materials (AMX₃), thereby affording devices with extended stability as well as state-of-the art efficiencies approaching those of the 3D materials. These films are made by spin-coating precursor solutions with an arbitrarily large average layer thickness <i>n</i> (⟨<i>n</i>⟩ > 7) to give films with both 2D and 3D phases. Although the 2D and 3D perovskite film formation mechanisms have been studied, little is understood about composite 2D/3D film formation. We used <i>in-situ</i> grazing-incidence wide-angle scattering with synchrotron radiation to characterize the films fabricated from precursor solutions with stoichiometries of (BA)₂(MA)_n−1Pb_nI_3n+1 (⟨<i>n</i>⟩ = 3, 4, 5, 7, 12, 50, and ∞ (MAPbI₃)). Four different mechanisms are seen depending on the stoichiometry in the precursor solution. Kinetic analysis shows faster and earlier growth of the solvate with increasing ⟨<i>n</i>⟩.

Exciton-Phonon Coupling and Low Energy Emission in 2D and Quasi-2D BA2MAn-1PbnI3n+1 Thin Films with Improved Phase Purity.

Phonon scattering with photogenerated excitons and free charges greatly affects optoelectronic properties of metal halide perovskites and governs their emission line width. Benefiting from the improved phase purity, we are able to analyze exciton-phonon coupling in 2D and quasi-2D BA2MAn-1PbnI3n+1 (n = 1-3) thin films using temperature-dependent photoluminescence (PL) spectroscopy. The layer thickness (n value) dependent coupling of free excitons with both acoustic and longitudinal optical (LO) phonons was extracted quantitatively by fitting the temperature-dependent PL line width and band gap. The low energy emissive signatures below free excitons at low temperature might belong to the emission of self-trapped excitons and bounded excitons in structural defects. Our findings provide a systematic picture for the layer thickness (n value) dependent exciton-phonon coupling in 2D and quasi-2D perovskite thin films and could be helpful for improving the optoelectronic performance of devices made by Ruddlesden-Popper perovskite thin films.

Donor-acceptor-donor type organic spacer for regulating the quantum wells of Dion-Jacobson 2D perovskites

Two-dimensional (2D) metal halide perovskite system has attracted significant attentions due its tunable optoelectronic characteristics and outstanding environmental durability. However, quantum wells (QWs) of 2D perovskite severely restrain the charge transfer between organic/inorganic layers, resulting in the significantly lower photovoltaic performance of 2D perovskite solar cells (PSCs) in contrast to their 3D analogues. To intrinsically refine the QW structures of 2D perovskite for less quantum confinement, we innovatively design the D-A-D (D: donor; A: acceptor) type organic cation as 2D spacer. The push-pull effects between D, A unit endows the organic spacer intramolecular charge transfer characteristic, which effectively lower its bandgap. The resulting 2D perovskite demonstrates flattened energy landscape of the QWs, which suppresses the charge transfer barrier and elongates the carrier diffusion lengths in 2D perovskite film. As a result, optoelectronic properties of this new 2D perovskite resemble those of the 3D counterparts, delivering an impressive PCE of 18.6% for 2D (n = 4) PSCs. This is one of the highest reported efficiency for DJ-type 2D perovskite (n ≤ 4) to date. By rationally selecting other D and A unit, QW structures of 2D perovskites can be further adjusted, which opens huge possibilities for developing a new system of 2D perovskites.

Tuning structural isomers of phenylenediammonium to afford efficient and stable perovskite solar cells and modules

Organic halide salt passivation is considered to be an essential strategy to reduce defects in state-of-the-art perovskite solar cells (PSCs). This strategy, however, suffers from the inevitable formation of in-plane favored two-dimensional (2D) perovskite layers with impaired charge transport, especially under thermal conditions, impeding photovoltaic performance and device scale-up. To overcome this limitation, we studied the energy barrier of 2D perovskite formation from ortho-, meta- and para-isomers of (phenylene)di(ethylammonium) iodide (PDEAI2) that were designed for tailored defect passivation. Treatment with the most sterically hindered ortho-isomer not only prevents the formation of surficial 2D perovskite film, even at elevated temperatures, but also maximizes the passivation effect on both shallow- and deep-level defects. The ensuing PSCs achieve an efficiency of 23.9% with long-term operational stability (over 1000 h). Importantly, a record efficiency of 21.4% for the perovskite module with an active area of 26 cm2 was achieved.

Synergistic Effect of Additives on 2D Perovskite Film Towards Efficient and Stable Solar Cell

Recently，layered Ruddlesden–Popper (RP) phase 2D halide perovskites have attracted tremendous attention due to their excellent environment stability and wide tunability on optoelectronic properties. However, the inhibition of out-of-plane charge transport limits the photovoltaic performance of 2D-based perovskite solar cells (PVSCs). To this respect, an orientation control of crystal growth in layered 2D perovskites has been proven to be effective method to manipulate the carrier transport. Here, we report a new approach to achieve orientation regulation of 2D perovskite via the synergistic effect of dimethyl sulfoxide (DMSO) and thio-semicarbazide (TSC) additives. The 2D (BA)2(MA)3Pb4I13 (BA = n-butylammonium, MA = methylammonium) perovskite films treated with DMSO and TSC additives show uniform morphology, increased grain size, intensified crystallinity and vertical orientation, resulting in reduced trap-state density and improved charge transport properties. The PVSCs assembled from these films yield a significant enhancement in PCE from 1.05% to 14.15% and an excellent environment stability. An unsealed device retains 90.3% of its initial PCE after 720 h storage in air atmosphere with relative humidity of 25 ± 5% at 25 °C. This work provides a possibility to fabricate high-quality 2D perovskite films and gives guidance for additive engineering for efficient and stable 2D PVCSs in future.

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

2D lead halide perovskites, which exhibit bandgap tunability and increased chemical stability, have been found to be useful for designing optoelectronic devices. Reducing dimensionality with decreasing number of layers (n=10-1) also imparts resistance to light-induced ion migration as seen from the halide ion segregation and dark recovery in mixed halide (Br:I=50:50) perovskite films. The light-induced halide ion segregation efficiency, as determined from difference absorbance spectra, decreases from 20% to <1%as the dimensionality is decreased for 2D perovskite film from n=10 to 1. The segregation rate constant (ksegregation ), which decreases from 5.9×10-3 s-1 (n=10) to 3.6×10-4 s-1 (n=1), correlates well with nearly an order of magnitude decrease observed in charge-carrier lifetime (τaverage =233ps for n=10vs τavg =27ps for n=1). The tightly bound excitons in 2D perovskites make charge separation less probable, which in turn decreases the halide mobility and resulting phase segregation. The importance of controlling the dimensionality of the 2D architecture in suppressing halide ion mobility is discussed.

Anion regulation engineering for efficient Ruddlesden-Popper inverted perovskite solar cells

Recently, many studies have focused on exploiting new spacer cations to boost the power conversion efficiency (PCE) of Quasi-two-dimensional (Q-2D) Ruddlesden-Popper (RP) perovskites solar cells (PSCs). As another essential part of RP perovskite structure, halogen anions have a substantial impact on crystalline quality. However, there are few studies about how halogen anions affect RP PSCs and their possible underlying mechanisms. Here, we investigate different halide anions that impact the optoelectronic properties of RP perovskite films. Specifically, we use PEAI, PEABr, and PEACl (PEA = phenethylammonium) to fabricate RP perovskite films based on PEA 2 MA 3 Pb 4 I 11 X 2 (X = I, Br or Cl, n = 4) for systematical study. Through a series of characterizations and analyses, RP perovskite films with PEACl show a higher proportion of vertical crystal orientation and fewer trap-states, which leads to improved carrier transmission pathways. As a result, the devices based on PEACl (PEA 2 MA 3 Pb 4 I 11 Cl 2 , n = 4) achieve a champion PCE of 12.02%, which is higher than PEAI (6.76%, PEA 2 MA 3 Pb 4 I 13 , n = 4) and PEABr (4.26%, PEA 2 MA 3 Pb 4 I 11 Br 2 , n = 4). • The effect of halogen anions on 2D PSCs is systematically investigated. • The Cl − contributes to the vertical orientation of 2D perovskite film. • The Br − impairs the crystallization quality in 2D perovskite film. • RP PSCs based on PEA 2 MA 3 Pb 4 I 11 Cl 2 achieves a champion PCE of 12.02%. • PSCs of PEA 2 MA 3 Pb 4 I 11 Cl 2 retains 97.1% of its initial PCE after 500 h.

High-phase purity two-dimensional perovskites with 17.3% efficiency enabled by interface engineering of hole transport layer

State-of-the-art p-i-n-based 3D perovskite solar cells (PSCs) use nickel oxide (NiOX) as an efficient hole transport layer (HTL), achieving efficiencies >22%. However, translating this to phase-pure 2D perovskites has been unsuccessful. Here, we report 2D phase-pure Ruddlesden-Popper BA2MA3Pb4I13 perovskites with 17.3% efficiency enabled by doping the NiOX with Li. Our results show that progressively increasing the doping concentration transforms the photoresistor behavior to a typical diode curve, with an increase in the average efficiency from 2.53% to 16.03% with a high open-circuit voltage of 1.22 V. Analysis reveals that Li doping of NiOX significantly improves the morphology, crystallinity, and orientation of 2D perovskite films and also affords a superior band alignment, facilitating efficient charge extraction. Finally, we demonstrate that 2D PSCs with Li-doped NiOX exhibit excellent photostability, with T99 = 400 h at 1 sun and T90 of 100 h at 5 suns measured at relative humidity of 60% ± 5% without the need for external thermal management.

2D Hybrid Halide Perovskites: Structure, Properties, and Applications in Solar Cells.

2D metal-halide perovskites have attracted intense research interest due to superior long-term stability under ambient environments. Compared to their 3D analog, the alternate arrangement of organic and inorganic layers leads to forming a multilayer quantum well (MQW), which endows 2D perovskites with anisotropic optoelectronic properties. In addition, the spacer layer functions as a hydrophobic barrier to effectively prevent 2D perovskite films from ion migration and moisture penetrating, thus realizing outstanding stability. Recently, 2D perovskites have been widely developed with abundant species. The stunning photovoltaic performance with the coexistence of long-term stability and high-power conversion efficiency (PCE) has been realized in 2D perovskite solar cells (PSCs), which paves an avenue for commercialization of PSCs. This review begins with an introduction of crystal structure and crystallization kinetics to illustrate the unique layer characters in 2D perovskites. Then, electron structure, excitons, dielectric confinement, and intrinsic stability properties are discussed in detail. Next, the photovoltaic performance based on recent Ruddlesden-Popper (RP), Dion-Jacobson (DJ), and alternating cations in the interlayer (ACI) phase 2D-PSCs is comprehensively summarized. Finally, the confronting challenges and strategies toward structural design and optoelectronic studies of 2D perovskites are proposed to offer insight into the advanced underlying properties of this family of materials.

Surface Passivation Using N-Type Organic Semiconductor by One-Step Method in Two-Dimensional Perovskite Solar Cells

Surface passivation, which has been intensively studied recently, is essential for the perovskite solar cells (PSCs), due to the intrinsic defects in perovskite crystal. A series of chemical or physical methods have been published for passivating the defects of perovskites, which effectively suppressed the charge recombination and enhanced the photovoltaic performance. In this study, the n-type semiconductor of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) is dissolved in chlorobenzene (CB) for the surface passivation during the spin-coating process for depositing the two-dimensional (2D) perovskite film. This approach simplifies the fabrication process of 2D PSCs and benefits the film quality. As a result, the defects of perovskite film are effectively passivated by this method. A better perovskite/PCBM heterojunction is generated, exhibiting an increased film coverage and improved film morphology of PCBM. It is found that this technology results in an improved electron transporting performance as well as suppressed charge recombination for electron transport layer. As a result, PSCs based on the one-step formed perovskite/PCBM heterojunctions exhibit the optimized power conversion efficiency of 15.69% which is about 37% higher than that of regular perovskite devices. The device environmental stability is also enhanced due to the quality improved electron transport layer.

Tuning Hybrid exciton–Photon Fano Resonances in Two-Dimensional Organic–Inorganic Perovskite Thin Films

As easy-to-grow quantum wells with narrow excitonic features at room temperature, two-dimensional (2D) Ruddleson-Popper perovskites are promising for realizing novel nanophotonic devices based on exciton-photon interactions. Here, we demonstrate a distinct hybrid exciton-photon Fano resonance in (C4H9NH3)2PbI4 thin films prepared via spin coating. Using a classical coupled-oscillator model and finite-difference time-domain simulations, we link the Fano interference to the coupling of the exciton with the Rayleigh-like scattering of the film microstructure. Combining colloidal plasmonic cavities with the 2D perovskite films, we demonstrate tuning of the Fano resonance. In combination with silver nanoparticles, the exciton-photon Fano interference couples to the in-plane plasmonic modes with indications of Rabi splitting. By creating a nanoparticle on mirror geometry, we address the out-of-plane excitonic component, reaching an intermediate coupling regime. These structures suggest possible photonic targets for biomolecular self-assembly applications.

Memory Seeds Enable High Structural Phase Purity in 2D Perovskite Films for High-Efficiency Devices.

2D perovskites are a class of halide perovskites offering a pathway for realizing efficient and durable optoelectronic devices. However, the broad chemical phase space and lack of understanding of film formation have led to quasi-2D perovskite films with polydispersity in perovskite layer thicknesses, which have hindered device performance and stability. Here, a simple and scalable approach is reported, termed as the "phase-selective method", to fabricate 2D perovskite thin films with homogenous layer thickness (phase purity). The phase-selective method involves the dissolution of single-crystalline powders with a homogeneous perovskite layer thickness in desired solvents to fabricate thin films. In situ characterizations reveal the presence of sub-micrometer-sized seeds in solution that preserve the memory of the dissolved single crystals and dictate the nucleation and growth of grains with an identical thickness of the perovskite layers in thin films. Photovoltaic devices with a p-i-n architecture are fabricated with such films, which yield an efficiency of 17.1% enabled by an open-circuit voltage of 1.20 V,while preserving 97.5% of their peak performance after 800 h under illumination without any external thermal management.

Elastic modulus tailoring in CH3NH3PbI3 perovskite system by the introduction of two dimensionality using (5-AVA)2PbI4

The stiffness of the perovskite active layer plays a critical role in influencing the flexibility of a solar cell. This is one of the important parameters which must be considered while deciding the architecture of the flexible device. Till now, there have been limited studies on the mechanical properties of 2D and 3D perovskite thin films. In this study, we report the very first time, the elastic modulus of the most commonly used 3D perovskite i.e. methylammonium lead iodide (MaPbI3), the pure 2D perovskite (5-AVA)2PbI4 which is based on 5-aminovaleric acid (5-AVA) cation as well as the 2D-3D mixed perovskites thin films through nanoindentation technique. The elastic modulus for the 3D perovskite has been found to be around 16.5 GPa, while it decreases to 6.3 GPa for pure 2D perovskite. The experimental results have also been corroborated by density functional theory calculations done for the 2D and 3D perovskite. The 2D perovskite shows a much lower modulus than the 3D perovskite and can be used within a 2D-3D mixture for improving the mechanical flexibility of the active layer. Also, it is well established that 2D perovskites are much more stable against moisture as compared to their 3D counterparts due to the presence of hydrophobic organic alkyl ammonium cation. Thus, the device containing an active layer comprising of a mixture of 3D and 2D perovskite can be used to improve the environmental stability of the overall device in addition to achieving mechanical durability.

Organic Ammonium Halide Modulators as Effective Strategy for Enhanced Perovskite Photovoltaic Performance.

Despite rapid improvements in efficiency, long‐term stability remains a challenge limiting the future up‐scaling of perovskite solar cells (PSCs). Although several approaches have been developed to improve the stability of PSCs, applying ammonium passivation materials in bilayer configuration PSCs has drawn intensive research interest due to the potential of simultaneously improving long‐term stability and boosting power conversion efficiency (PCE). This review focuses on the recent advances of improving n‐i‐p PSCs photovoltaic performance by employing ammonium halide‐based molecular modulators. The first section briefly summarizes the challenges of perovskite materials by introducing the degradation mechanisms associated with the hygroscopic nature and ion migration issues. Then, recent reports regarding the roles of overlayers formed from ammonium‐based passivation agents are discussed on the basis of ligand and halide effects. This includes both the formation of 2D perovskite films as well as purely organic passivating layers. Finally, the last section provides future perspectives on the use of organic ammonium halides within bilayer‐architecture PSCs to improve the photovoltaic performances. Overall, this review provides a roadmap on current demands and future research directions of molecular modulators to address the critical limitations of PSCs, to mitigate the major barriers on the pathway toward future up‐scaling applications.

Excitonic Solar Cells Using 2D Perovskite of (BA)2(FA)2Pb3I10

Using substrates at room temperature or at 110 °C, two-dimensional (2D) perovskite films and solar cells using mixed butylammonium (BA) and formamidinium (FA) cations, i.e., (BA)2(FA)n−1PbnI3n+1 (n...

Breakthrough: Phase-Pure 2D Perovskite Films

Obtaining phase-pure 2D perovskite films will extend the understanding and applications in various optoelectronic fields. Recently in <i>Nature Energy</i>, Liang and coworkers first present phase-pure 2D perovskites by replacing BAI with BAAc, showing stronger ionic coordination with the perovskite framework. A PCE of 16.25% with enhanced stability was obtained.

Photo-response of Two-Dimensional Ruddlesden-Popper Perovskite Films for Photovoltaics

Two-dimensional (2D) Ruddlesden-Popper (RP) perovskites have emerged as a prospective candidate to address the instability issues of traditional perovskite solar cells. However, the mechanisms of charge carrier transport of 2D perovskite films obtained by the solution process still remain elusive. In this work, we proposed a novel characterization technique based on the Kelvin probe force microscopy (KPFM) to investigate the micro-scale morphology and surface potential (SP) of the BA2MA3Pb4I13 films. In additionally, a Xenon laser source was adopted to realize the in-situ scanning of the light response of the perovskite film. The obvious increase in surface potential values in the same scanning area before and after white light illumination indicated the emergence of photo-generated charge carriers. Based on the unique photophysical properties and form formation features of the hot-cast BA2MA3Pb4I13 films, we fabricated the 2D perovskite solar cells (PSCs) with an efficiency of 10.95%. As a result, the in-situ KPFM is capable to serve as an effective approach to investigating the charge carrier behaviors in the 2D perovskites for photovoltaic applications.

Impact of grain size on the optoelectronic performance of 2D Ruddlesden–Popper perovskite-based photodetectors

This paper presents the synthesis of grain size-controlled 2D perovskite films for high-performance photodetectors by combining solvent engineering and hot casting.

Perpendicularly oriented 2D perovskite thin films prepared using the bar-coating method and DMSO additive.

A 2D perovskite incorporating an amine moiety with a carboxy group exhibited orientation changes as the amount of DMSO additive varied. The degree of perpendicular orientation was increased by optimizing the amount of DMSO additive, while using the bar-coating method. Moreover, film thickness and the ratio of perpendicular orientation exhibited a positive correlation.