Layered Halide Perovskites Research Articles

First-principles investigation on the thickness-dependent optoelectronic properties of two-dimensional perovskite BA2SnI4

Recently, Sn-based two-dimensional layered halide perovskites(Sn-2DLHP) with fine light-harvesting performances and longstanding stabilities have attracted considerable interests. However, the impact of thickness on the optoelectronic properties of Sn-2DLHP is still insufficiently known. In this work, we take BA2SnI4(BA=C4H9NH3+) as a representative to present theoretical studies of electronic structure, carrier mobilities, optical absorption, and exciton-binding energy to reveal the effect of thickness on the optoelectronic properties of Sn-2DLHP. Results show that the 2D-layered BA2SnI4 are direct bandgap semiconductors with absorption coefficients of up to 105 cm−1 and appreciable carrier mobilities, which all can be significantly modified by tuning thickness. Notably, the 2D-layered BA2SnI4 have large and thickness-dependent exciton-binding energies, indicating the 2D-layered BA2SnI4 may have more application potential in optoelectronic devices. Our theoretical work paves a theoretical foundation of potential applications for other Sn-2DLHP in optoelectronic devices.

Upgrading of methylammonium lead halide perovskite layers by thermal imprint

The manufacturing of devices from methylammonium-based perovskites asks for reliable and scalable processing. As solvent engineering is not the option of choice to obtain homogeneous layers on large areas, our idea is to ‘upgrade’ a non-perfect pristine layer by recrystallization in a thermal imprint step (called ‘planar hot pressing’) and thus to reduce the demands on the layer formation itself. Recently, imprint has proven both its capability to improve the crystal size of perovskite layers and its usability for large area manufacturing. We start with methylammonium lead bromide layers obtained from a conventional solution-based process. Acetate is used as a competitive lead source; even under perfect conditions the resulting perovskite layer then will contain side-products due to layer formation besides the desired perovskite. Based on the physical properties of the materials involved we discuss the impact of the temperature on the status of the layer both during soft-bake and during thermal imprint. By using a special imprint technique called ‘hot loading’ we are able to visualize the upgrade of the layer with time, namely a growth of the grains and an accumulation of the side-products at the grain boundaries. By means of a subsequent vacuum exposition we reveal the presence of non-perovskite components with a simple inspection of the morphology of the layer; all experiments are supported by X-ray and electron diffraction measurements. Besides degradation, we discuss recrystallization and propose post-crystallization to explain the experimental results. This physical approach towards perovskite layers with large grains by post-processing is a key step towards large-area preparation of high-quality layers for device manufacturing.

Effects of All-Organic Interlayer Surface Modifiers on the Efficiency and Stability of Perovskite Solar Cells.

Surface imperfections created during fabrication of halide perovskite (HP) films could induce formation of various defect sites that affect device performance and stability. In this work, all-organic surface modifiers consisting of alkylammonium cations and alkanoate anions are introduced on top of the HP layer to passivate interfacial vacancies and improve moisture tolerance. Passivation using alkylammonium alkanoate does not induce formation of low-dimensional perovskites species. Instead, the organic species only passivate the perovskite's surface and grain boundaries, which results in enhanced hydrophobic character of the HP films. In terms of photovoltaic application, passivation with alkylammonium alkanoate allows significant reduction in recombination losses and enhancement of open-circuit voltage. Alongside unchanged short-circuit current density, power conversion efficiencies of more than 18.5 % can be obtained from the treated sample. Furthermore, the unencapsulated device retains 85 % of its initial PCE upon treatment, whereas the standard 3D perovskite device loses 50 % of its original PCE when both are subjected to ambient environment over 1500 h.

Layer Shift Factor in Layered Hybrid Perovskites: Univocal Quantitative Descriptor of Composition–Structure–Property Relationships

Asceding interest of the scientific community in layered hybrid halide perovskites (LHHPs) as materials for innovative photovoltaic and optoelectronic applications led to unprecedented expansion of this family of compounds, reaching now several hundred refined structures. Despite the unique structural diversity of LHHPs, traditional approaches of describing their structures, such as dividing into Dion-Jacobson (DJ) or Ruddlesden-Popper (RP) phases for mostt structures are ambiguous and unquantifiable. Here, we introduced a quantitative layer shift factor (LSF) for a univocal classification and quantitative comparison of the structures. We also developed an algorithm for automatic calculation of the LSF for such structures. We demonstrate the application of the proposed approach for an analysis of correlations between LSF and band gap to reveal "structure-property" relationships. Our study gives a simple and useful approach to classify of either the layered perovskite-like structures or other layered compounds composed of layers of vertex-connected octahedra as a structural unit.

A study of the performance of organometal trihalide perovskite solar cell due to defects in bulk CH3NH3PbI3 (MAPI) perovskite layer

In this numerical simulation research, we have investigated device performances of p-i-n type organometal trihalide perovskite solar cell by introducing deep and shallow defects in the bulk halide perovskite layer. The organometal halide perovskite solar cell device structure has Glass/ITO/PEDOT:PSS/Bulk-MAPI/2D-MAPI/PCBM/Ag. The open-circuit voltage of the solar cell was decreased due to both shallow and deep defects of the bulk-MAPI layer which increase the recombination of electron-hole pairs in the solar cell. The dark saturation current, which causes to reduce the open-circuit voltage of the solar cell, was increased due to the deep defects in the bulk-MAPI layer. Therefore, the power conversion efficiency of the solar cell can be enhanced by minimizing the deep defects in the bulk-MAPI layer, which can increase the open-circuit voltage of the solar cell by suppressing the effect of dark saturation current. We have verified that Shockley-Read-Hall (SRH) recombination is the most predominant recombination mechanism when only the deep defects are presented in the bulk-MAPI layer. Also, this investigation has proved, that Radiative recombination has become the most predominant recombination mechanism when the shallow defects are presented in the bulk-MAPI layer by completely omitting the deep defects of the bulk-MAPI layer. Finally, our model verified that the dark saturation current of the solar cell controls the open-circuit voltage when the recombination is occurring in the solar cell. Iodine interstitial defects that mainly act as deep defects in the bulk-MAPI layer should be minimized to increase the overall solar cell performance and power conversion efficiency of the organometal trihalide perovskite solar cell device. KEYWORDS: Perovskite-Based Solar Cell, Recombination, Dark Saturation Current, Defects, Power-Conversion Efficiency

Alloying a single and a double perovskite: a Cu+/2+ mixed-valence layered halide perovskite with strong optical absorption.

Introducing heterovalent cations at the octahedral sites of halide perovskites can substantially change their optoelectronic properties. Yet, in most cases, only small amounts of such metals can be incorporated as impurities into the three-dimensional lattice. Here, we exploit the greater structural flexibility of the two-dimensional (2D) perovskite framework to place three distinct stoichiometric cations in the octahedral sites. The new layered perovskites AI4[CuII(CuIInIII)0.5Cl8] (1, A = organic cation) may be derived from a CuI–InIII double perovskite by replacing half of the octahedral metal sites with Cu2+. Electron paramagnetic resonance and X-ray absorption spectroscopy confirm the presence of Cu2+ in 1. Crystallographic studies demonstrate that 1 represents an averaging of the CuI–InIII double perovskite and CuII single perovskite structures. However, whereas the highly insulating CuI–InIII and CuII perovskites are colorless and yellow, respectively, 1 is black, with substantially higher electronic conductivity than that of either endmember. We trace these emergent properties in 1 to intervalence charge transfer between the mixed-valence Cu centers. We further propose a tiling model to describe how the Cu+, Cu2+, and In3+ coordination spheres can pack most favorably into a 2D perovskite lattice, which explains the unusual 1 : 2 : 1 ratio of these cations found in 1. Magnetic susceptibility data of 1 further corroborate this packing model. The emergence of enhanced visible light absorption and electronic conductivity in 1 demonstrates the importance of devising strategies for increasing the compositional complexity of halide perovskites.

Unravelling the Behavior of Dion–Jacobson Layered Hybrid Perovskites in Humid Environments

Layered hybrid halide perovskites are known to be more environmentally stable than their 3D analogues. The enhanced stability is particularly relevant for Dion–Jacobson-type layered perovskites due...

Spectral Instability of Layered Mixed Halide Perovskites Results from Anion Phase Redistribution and Selective Hole Injection.

Despite the ability to precisely tune their bandgap energies, mixed halide perovskites (MHPs) suffer from significant spectral instability, which obstructs their utilization for the rational design of light-emitting diodes. Here, we investigate the origin of the electroluminescence peak shifts in layered MHPs containing bromide and iodide. X-ray diffraction and steady-state absorption measurements prove effective integration of iodide into the cubic lattice and the spatially uniform distribution of halides in the ambient environment. However, the applied electric field during the device operation is found to drive the systematic halide migration. Quantum mechanical density functional theory calculations reveal that the different activation energies required for directional ion hopping lead to the redistribution of anions. In-depth analyses of the electroluminescence spectra indicate that the spectral shifting rate is dependent on the drift velocity of halides. Finally, it is suggested from our study that the dominant red emission is ascribed to the thermodynamically favorable selective hole injection. Our mechanistic study provides insights into the fundamental reason for the spectral instability of devices based on MHPs.

Electronic structure and optical properties of SnO2/HC(NH2)2PbI3 interfaces from first-principles calculations

Interface engineering of the device layers of halide perovskite solar cells has shown the potential to improve efficiency and stability. In this paper, the interface mechanism between the halide perovskite layer FAPbI3 and SnO2 was clarified by first-principles calculations. Results showed that the formation energies of the FAI interface and the PbI2 interface were -0.107eV and -0.087eV respectively. Compared with the PbI2 interface, the FAI interface has lower binding energy, which means that the FAI interface is more conducive to the formation. The analysis of structural deformation shows that the structure of the FAI interface is more stable. The density of states analysis shows that I-p, Pb-p, O-p, Sn-s, Sn-d are strongly hybridized. The analysis of the dielectric function shows that the FAI interface has better charge storage capacity and higher conductivity.

Ruddlesden-Popper-Phase Hybrid Halide Perovskite/Small-Molecule Organic Blend Memory Transistors.

Controlling the morphology of metal halide perovskite layers during processing is critical for the manufacturing of optoelectronics. Here, a strategy to control the microstructure of solution-processed layered Ruddlesden-Popper-phase perovskite films based on phenethylammonium lead bromide ((PEA)2 PbBr4 ) is reported. The method relies on the addition of the organic semiconductor 2,7-dioctyl[1]benzothieno[3,2-b]benzothiophene (C8 -BTBT) into the perovskite formulation, where it facilitates the formation of large, near-single-crystalline-quality platelet-like (PEA)2 PbBr4 domains overlaid by a ≈5-nm-thin C8 -BTBT layer. Transistors with (PEA)2 PbBr4 /C8 -BTBT channels exhibit an unexpectedly large hysteresis window between forward and return bias sweeps. Material and device analysis combined with theoretical calculations suggest that the C8 -BTBT-rich phase acts as the hole-transporting channel, while the quantum wells in (PEA)2 PbBr4 act as the charge storage element where carriers from the channel are injected, stored, or extracted via tunneling.When tested as a non-volatile memory, the devices exhibit a record memory window (>180V), a high erase/write channel current ratio (104 ), good data retention, and high endurance (>104 cycles). The results here highlight a new memory device concept for application in large-area electronics, while the growth technique can potentially be exploited for the development of other optoelectronic devices including solar cells, photodetectors, and light-emitting diodes.

Photoelectrochemical and first-principles investigation on perylene dye-based perovskite/TiO2 photoelectrode

The halide perovskite/TiO2 materials have been extensively employed for solar cells; however, they suffer from limited optoelectronic performance and stability in aqueous solution. In this manuscript, we employ a commercially available perylene dye, namely perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), between the halide perovskite layer and the TiO2 layer, to improve the photoelectrochemical properties of the prototypical CH3NH3PbI3/TiO2 film in the aqueous solution. The incorporation of the perylene dye into the perovskite photoanode induces a photocurrent value twice as much as that offered by the bare perovskite-based film in the aqueous solution. The first-principles calculations suggest that the adsorption of the perylene dye molecule on the halide perovskite substrate is stable and the dye/perovskite interfacial structure depends on the perovskite surface terminations: for the PbI2-terminated perovskite surface, the perylene dye molecule interacts with the perovskite surface via the O⋯Pb contact; for the CH3NH3I-terminated perovskite surface, the perylene dye molecule interacts with the perovskite surface via the H⋯N contact. This study facilitates the fundamental understanding of the dye-sensitized halide perovskite materials for optoelectronic applications.

(Invited) Atomic Layer Deposition of Charge Transport Layers for Highly Efficient and Stable Perovskite Photovoltaics

Atomic layer deposition (ALD) is now being recognized as a powerful, general tool for modifying the surfaces of nanomaterials in applications for many renewable energy conversion devices. ALD techniques are now utilizing in charge transporting layers for solar cells. CH3NH3PbI3 with perovskite crystal structure has attracted considerable interest for high power conversion efficiency (PCE, now certified 25.2 %). ALD chemistry for TiO2, NiO, SnO2, and ZnO are well known and the process requires relatively low deposition temperature as low as ~ 100 °C, which is applicable to deposit onto the halide perovskite layer. In this presentation, highly efficient perovskite solar cells having a long-term stability that adapts uniform and dense inorganic charge transport layers grown by ALD are reported. The devices showed excellent water-resistant properties and long-term stability at 85 °C under illumination. Figure 1

Theoretical investigation on interactions between lithium ions and two-dimensional halide perovskite for solar-rechargeable batteries

Two-dimensional (2D) halide perovskite materials have recently been proposed for solar energy conversion and energy storage systems, namely, photo-rechargeable batteries. However, the theoretical understanding of the 2D halide perovskite materials for the photo-rechargeable batteries lags behind the experimental advancement. In this manuscript, we investigate the adsorption and transport properties of lithium ions on an experimentally verified 2D halide perovskite material, (C6H9C2H4NH3)2PbI4, via first-principles calculations. Our study reveals the efficient adsorption and transport properties of the lithium ion at the 2D lead halide perovskite surface, and demonstrates the prospects of the metal halide perovskite system as an effective anode material for lithium-ion batteries as well as the photo-charging medium for photo-rechargeable batteries. In addition, the interlayer diffusion of the lithium ions is calculated, which demonstrates the efficient transport of the lithium ions between the 2D halide perovskite layers that contribute to the most of capacity. Most importantly, the displacement of the lithium ion is demonstrated to be available upon the hole polaron formation, which is suggested to signify the photo-charging behaviour initiating the unidirectional lithium ion movement on the electrode surface. The present study for the first time rationalizes the photo-charging behaviour of the photo-rechargeable battery, and facilitates the fundamental understanding on the halide perovskites for the energy storage applications including the lithium-ion batteries and the photo-rechargeable batteries.

Naphthalenediimide Cations Inhibit 2D Perovskite Formation and Facilitate Subpicosecond Electron Transfer

Layered metal halide perovskites, also called perovskite quantum wells (PQWs), are versatile optoelectronic materials possessing large oscillator strengths, band gaps tuned via the quantum size eff...

The chemistry and energetics of the interface between metal halide perovskite and atomic layer deposited metal oxides

The chemistry of the interface between the metal halide perovskite absorber and the charge transport layer affects the performance and stability of metal halide perovskite solar cells (PSCs). The literature provides several examples of poor PSC conversion efficiency values, when electron transport layers (ETLs), such as SnO2 and TiO2, are processed by atomic layer deposition (ALD) directly on the perovskite absorber. In the present work, we shed light on the chemical modifications occurring at the perovskite surface, during ALD processing of SnO2 and TiO2, in parallel with the evaluation of the PSC cell performance. The ALD processes are carried out on a (Cs,FA)Pb(I,Br)3 perovskite by adopting tetrakis(dimethylamino)tin(IV) and tetrakis(dimethylamino)titanium(IV) as metal precursors and H2O as the coreactant for SnO2 and TiO2, respectively. Perovskite surface modification occurs in the form of an ultrathin PbBr2 layer. Furthermore, in the case of SnO2, halogen molecules are detected at the interface, in parallel with the initial growth of an oxygen-deficient SnO2. Subgap defect states just above the valence band maximum of SnO2 are also detected. These states act as hole traps at the perovskite/SnO2 interface, subsequently promoting charge recombination and deteriorating the performance of the cell. We hypothesize that a redox reaction between the perovskite, or its decomposition products, and the Sn metal center of the ALD precursor takes place: I− and Br− are oxidized to I2 and Br2, respectively, and Sn(IV) is reduced to Sn(II). In contrast, the Ti(IV) metal center does not undergo any redox process, and, as a result, a promising 11% power conversion efficiency is measured with TiO2 as the ETL. This result strongly suggests that TiO2 may be a more suitable ETL, when processed directly on the perovskite absorber.

Near‐Infrared‐Transparent Perovskite Solar Cells and Perovskite‐Based Tandem Photovoltaics

AbstractMetal halide perovskite solar cells (PSCs) have gained tremendous attention due to their high power conversion efficiencies (PCEs) and potential for low‐cost manufacturing. Their wide and tunable bandgap makes perovskites an ideal candidate for tandem solar cells (TSCs) with well‐established narrow bandgap photovoltaic technologies, such as crystalline silicon and Cu(In,Ga)Se2, to boost the PCEs beyond the Shockley–Queisser limit at affordable additional cost. Although perovskite‐based TSCs have shown rapid progress over the past few years, they are far from reaching their practical efficiency limit. In addition, technology commercialization needs to overcome several challenges such as processing upscalability and long‐term operational stability of solar modules. In this review, a comprehensive overview of the recent progress of perovskite‐based TSCs is provided and the key challenges in the field are discussed. First, the structural and optoelectronic properties of metal halide perovskite materials and preparation methods of metal halide perovskite layers are introduced. Next, the important constituents of near‐infrared (NIR) transparent PSCs for achieving high efficiency along with high NIR transmittance are highlighted. Then the developments in perovskite‐based TSCs are reviewed, the limiting factors are outlined, and strategies to boost the efficiencies well beyond 30% are provided. Finally, the review is concluded by highlighting the bottlenecks for commercialization and providing an outlook for technology advancement.

Intrinsically Ultralow Thermal Conductivity in Ruddlesden-Popper 2D Perovskite Cs2PbI2Cl2: Localized Anharmonic Vibrations and Dynamic Octahedral Distortions.

Fundamental understanding of the correlation between chemical bonding and lattice dynamics in intrinsically low thermal conductive crystalline solids is important to thermoelectrics, thermal barrier coating, and more recently to photovoltaics. Two-dimensional (2D) layered halide perovskites have recently attracted widespread attention in optoelectronics and solar cells. Here, we discover intrinsically ultralow lattice thermal conductivity (κL) in the single crystal of all-inorganic layered Ruddlesden-Popper (RP) perovskite, Cs2PbI2Cl2, synthesized by the Bridgman method. We have measured the anisotropic κL value of the Cs2PbI2Cl2 single crystal and observed an ultralow κL value of ∼0.37-0.28 W/mK in the temperature range of 295-523 K when measured along the crystallographic c-axis. First-principles density functional theory (DFT) analysis of the phonon spectrum uncovers the presence of soft (frequency ∼18-55 cm-1) optical phonon modes that constitute relatively flat bands due to localized vibrations of Cs and I atoms. A further low energy optical mode exists at ∼12 cm-1 that originates from dynamic octahedral rotation around Pb caused by anharmonic vibration of Cl atoms induced by a 3s2 lone pair. We provide experimental evidence for such low energy optical phonon modes with low-temperature heat capacity and temperature-dependent Raman spectroscopic measurements. The strong anharmonic coupling of the low energy optical modes with acoustic modes causes damping of heat carrying acoustic phonons to ultrasoft frequency (maximum ∼37 cm-1). The combined effect of soft elastic layered structure, abundance of low energy optical phonons, and strong acoustic-optical phonon coupling results in an intrinsically ultralow κL value in the all-inorganic layered RP perovskite Cs2PbI2Cl2.

Full Defects Passivation Enables 21% Efficiency Perovskite Solar Cells Operating in Air

AbstractThe lattice defects in the bulk and on the surface of the halide perovskite layer serve as trap sites and recombination centers to annihilate photogenerated carriers, determining the performance and stability of perovskite optoelectronic devices. Herein, the previously reported surface defects passivation engineering is extended to a full defects passivation strategy through stereoscopically introducing the cysteamine hydrochloride (CSA‐Cl) in the bulk and on the surface of perovskites. First‐principle density functional theory (DFT) calculations are employed to theoretically verify the multiple defects passivation effect of the CAS‐Cl on the perovskite. The perovskite layer with full defects passivation exhibits superior carrier dynamics as revealed by femtosecond transient absorption due to the reduced defect density determined by a highly sensitive photothermal deflection spectroscopy technique. Consequently, a high efficiency approaching 21% is achieved for the inverted planar perovskite solar cells (PVSCs). More importantly, the CAS‐Cl passivated PVSCs exhibit operation in air, which will be beneficial for the in situ device test for understanding the photophysics involved. This work provides a promising strategy to reduce the defects in both the perovskite bulk and surface for superior optoelectronic properties, facilitating the development of highly efficient and stable PVSCs and other optoelectronic devices.

Surface Property Tuning of Methylammonium Lead Iodide by Plasma for Use in Planar Perovskite Solar Cells.

The demand for cheap and green energy as a replacement for fossil fuels has never been greater, and perovskite solar cells (PSCs) are among the leading means of meeting it. The surface properties of metal halide perovskite layers play crucial roles in the performance and durability of such cells. Consequently, a wide range of engineering processes for surface modification of perovskite layers has been investigated and among them is atmospheric pressure plasma (APP). Nevertheless, knowledge of the interaction between plasma and perovskite layers is still far from complete. In this work, CH3NH3PbI3 films were subjected to APP generated by a portable plasma source. A detailed understanding of band energy after plasma treatment is crucial to the investigation of the behavior of the perovskite layer. This study demonstrates a remarkable shift in the valence and conduction bands of a perovskite layer after plasma treatment, while band gap energy remains relatively constant. We found that short plasma treatment of perovskite layers resulted in higher performance and stability of PSCs.

Phenolic antioxidant-incorporated durable perovskite layers and their application for a solar cell

Abstract