Tin Halide Perovskites Research Articles

First Experimental Evidence of Amorphous Tin Oxide Formation in Lead‐Free Perovskites by Spectroscopic Ellipsometry

The most promising lead‐free options for producing perovskite solar cells are tin halide perovskite materials. Herein, while in situ monitoring the optical evolution of the material in humid air, spectroscopic ellipsometry is used to investigate the dielectric function of FASnI3 layers (with and without additives) within the range of 1–5 eV. According to calculations based on the density functional theory that shows oxygen diffusion on FASnI3 surfaces, the steady decrease in absorption coefficient in the band gap region (1.47 eV) and simultaneous increase in absorption in the 3–4.5 eV region suggest the production of amorphous tin oxide. Concurrently, X‐ray diffraction reveals a clear degradation of FASnI3. With the addition of sodium borohydride and dipropylammonium iodide, the optically active area of about 1.47 eV is preserved for a longer period while SnO2 production is prevented. Last but not least, FASnI3's stability is investigated in dry N2 environment and shown that it is optically durable for thermal operations up to 100 °C, particularly when additives are used.

Enhancement of Efficiency and Stability for Tin Halide Perovskite Solar Cells by Using Improved Doping Method

AbstractIn recent years, tin halide perovskite solar cells (PKSCs) have emerged as a promising alternative to lead‐PKSCs. However, due to defects such as Sn4+ and iodide vacancies, their efficiency is lower than lead‐PKSCs. To address this issue, various strategies are proposed to improve the quality of perovskite, including copper iodide (CuI) doping. Unfortunately, the conventional solvent composition of DMF:DMSO = 4:1 has limited the solubility of CuI, resulting in inconsistent results and limited efficiency improvements. However, this research proposed a preprocessing method of CuI to decrease the defects and improve the perovskite layer's morphology. As a result, the efficiency of tin‐PKSCs with both P‐I‐N and hole transport layer (HTL) free structures is enhanced, increasing from 9.8% to 13.1% and 9.4% to 10.5%, respectively. Moreover, the doped tin‐PKSCs have exhibited better stability, retaining 75% of their initial power conversion efficiency (PCE) after being stored in a glovebox for 102 days.

Phase-pure 2D tin halide perovskite thin flakes for stable lasing.

Ruddlesden-Popper tin halide perovskites are a class of two-dimensional (2D) semiconductors with exceptional optoelectronic properties, high carrier mobility, and low toxicity. However, the synthesis of phase-pure 2D tin perovskites is still challenging, and the fundamental understanding of their optoelectronic properties is deficient compared to their lead counterparts. Here, we report the synthesis of a series of 2D tin perovskite bulk crystals with high phase purity via a mixed-solvent strategy. By engineering the quantum-well thickness (related to n value) and organic ligands, the optoelectronic properties, including photoluminescence emission, exciton-phonon coupling strength, and exciton binding energy, exhibit a wide tunability. In addition, these 2D tin perovskites exhibited excellent lasing performance. Both high-n value tin perovskite (n > 1) and n = 1 tin perovskite thin flakes were successfully optically pumped to lase. Furthermore, the lasing from 2D tin perovskites could be maintained up to room temperature. Our findings highlight the tremendous potential of 2D tin perovskites as promising candidates for high-performance lasers.

Boosting the Self-Trapped Exciton Emission in Cs4SnBr6 Zero-Dimensional Perovskite via Rapid Heat Treatment.

Zero-dimensional (0D) tin halide perovskites feature extraordinary properties, such as broadband emission, high photoluminescence quantum yield, and self-absorption-free characteristics. The innovation of synthesis approaches for high-quality 0D tin halide perovskites has facilitated the flourishing development of perovskite-based optoelectronic devices in recent years. However, discovering an effective strategy to further enhance their emission efficiency remains a considerable challenge. Herein, we report a unique strategy employing rapid heat treatment to attain efficient self-trapped exciton (STE) emission in Cs4SnBr6 zero-dimensional perovskite. Compared to the pristine Cs4SnBr6, rapid thermal treatment (RTT) at 200 °C for a duration of 120 s results in an augmented STE emission with the photoluminescence (PL) quantum yield rising from an initial 50.1% to a substantial 64.7%. Temperature-dependent PL spectra analysis, Raman spectra, and PL decay traces reveal that the PL improvement is attributed to the appropriate electron-phonon coupling as well as the increased binding energies of STEs induced by the RTT. Our findings open up a new avenue for efficient luminescent 0D tin-halide perovskites toward the development of efficient optoelectronic devices based on 0D perovskites.

Reduction of Hole Carriers by van der Waals Contact for Enhanced Photoluminescence Quantum Yield in Two-Dimensional Tin Halide Perovskite

Reduction of Hole Carriers by van der Waals Contact for Enhanced Photoluminescence Quantum Yield in Two-Dimensional Tin Halide Perovskite

Tin Halide Perovskite Solar Cells with Open-Circuit Voltages Approaching the Shockley-Queisser Limit.

The power conversion efficiency of tin-based halide perovskite solar cells is limited by large photovoltage losses arising from the significant energy-level offset between the perovskite and the conventional electron transport material, fullerene C60. The fullerene derivative indene-C60 bisadduct (ICBA) is a promising alternative to mitigate this drawback, owing to its superior energy level matching with most tin-based perovskites. However, the less finely controlled energy disorder of the ICBA films leads to the extension of its band tails that limits the photovoltage of the resultant devices and reduces the power conversion efficiency. Herein, we fabricate ICBA films with improved morphology and electrical properties by optimizing the choice of solvent and the annealing temperature. Energy disorder in the ICBA films is substantially reduced, as evidenced by the 22 meV smaller width of the electronic density of states. The resulting solar cells show open-circuit voltages of up to 1.01 V, one of the highest values reported so far for tin-based devices. Combined with surface passivation, this strategy enabled solar cells with efficiencies of up to 11.57%. Our work highlights the importance of controlling the properties of the electron transport material toward the development of efficient lead-free perovskite solar cells and demonstrates the potential of solvent engineering for efficient device processing.

Mechanistic Insight into the Precursor Chemistry of Cesium Tin Iodide Perovskite Nanocrystals

Colloidal tin halide perovskite nanocrystals (NCs) are of interest as an alternative to their lead-based counterparts. While some advancements have been achieved in their synthetic development, the reaction mechanism, especially the precursor chemistry, of tin halide perovskite NCs remains poorly understood. Here, using cesium tin iodide (CsSnI3) perovskite NCs as a model system, we report on the mechanistic insight into the precursor chemistry of tin-based perovskite NCs through a combination of infrared, mass spectrometry, and nuclear magnetic resonance spectroscopy. We identify that the active intermediate complexes, polymeric alkanoate iodides that form via the reaction of the iodide source with oligomers present in the tin(II) carboxylates, play a key role in governing the reactivity of the tin iodide precursor, which leads to the variation in the size, size uniformity, and photoluminescence quantum yield of CsSnI3 NCs. Our work underscores the importance of understanding the precursor chemistry as a key parameter to design and synthesize tin halide perovskite NCs, which not only aids in their syntheses by design but also might benefit the fabrication of high-quality polycrystalline tin-based films.

Morphology and Performance Enhancement through the Strong Passivation Effect of Amphoteric Ions in Tin-based Perovskite Solar Cells.

Despite the optoelectronic similarities between tin and lead halide perovskites, the performance of tin-based perovskite solar cells remains far behind, with the highest reported efficiency to date being ≈14%. This is highly correlated to the instability of tin halide perovskite, as well as the rapid crystallization behavior in perovskite film formation. In this work, l-Asparagine as a zwitterion plays a dual role in controlling the nucleation/crystallization process and improving the morphology of perovskite film. Furthermore, tin perovskites with l-Asparagine show more favorable energy-level matching, enhancing the charge extraction and minimizing the charge recombination, leading to an enhanced power conversion efficiency of 13.31% (from 10.54% without l-Asparagine) with remarkable stability. These results are also in good agreement with the density functional theory calculations. This work not only provides a facile and efficient approach to controlling the crystallization and morphology of perovskite film but also offers guidelines for further improved performance of tin-based perovskite electronic devices.

Electronic Structure and Optical Properties of Tin Iodide Solution Complexes.

The emerging interest in tin halide perovskites demands a robust understanding of the fundamental properties of these materials starting from the earliest steps of their synthesis. In a first-principles work based on time dependent density functional theory, we investigate the structural, energetic, electronic, and optical properties of 14 tin iodide solution complexes formed by the SnI2 unit tetracoordinated with molecules of common solvents, which we classify according to their Gutmann's donor number. We find that all considered complexes are energetically stable and their formation energy expectedly increases with the donating ability of the solvent. The energies of the frontier states are affected by the choice of solvent, with their absolute values decreasing with the donor number. The occupied orbitals are predominantly localized on the tin iodide unit, while the unoccupied ones are distributed also on the solvent molecules. Owing to this partial wave function overlap, the first optical excitation is generally weak, although the spectral weight is red-shifted by the solvent molecules being coordinated to SnI2 in comparison to the reference obtained for this molecule alone. Comparisons with results obtained on the same level of theory on Pb-based counterparts corroborate our analysis. The outcomes of this study provide quantum-mechanical insight into the fundamental properties of tin iodide solution complexes. This knowledge is valuable in the research on lead-free halide perovskites and their precursors.

Improved Structural Order and Exciton Delocalization in High-Member Quasi-Two-Dimensional Tin Halide Perovskite Revealed by Electroabsorption Spectroscopy

Engineering of quasi-two-dimensional (quasi-2D) tin halide perovskite structures is a promising pathway to achieve high-performance lead-free perovskite solar cells, with recently developed devices demonstrating over 14% efficiency. Despite the significant efficiency improvement over the bulk three-dimensional (3D) tin perovskite solar cells, the precise relationship between structural engineering and electron-hole (exciton) properties is not fully understood. Here, we study exciton properties in high-member quasi-2D tin perovskite (which is dominated by large n phases) and bulk 3D tin perovskite using electroabsorption (EA) spectroscopy. By numerically extracting the changes in polarizability and dipole moment between the excited and ground states, we show that more ordered and delocalized excitons are formed in the high-member quasi-2D film. This result indicates that the high-member quasi-2D tin perovskite film consists of more ordered crystal orientations and reduced defect density, which is in agreement with the over 5-fold increase in exciton lifetime and much improved solar cell efficiency in devices. Our results provide insights on the structure-property relationship of high-performance quasi-2D tin perovskite optoelectronic devices.

Ionic liquid functionalized tin halide perovskite investigated by STXM and spectro-ptychography

The structural and compositional properties of tin halide perovskites (CH(NH2)2SnI3, FASnI3) with and without an ionic liquid of 1-Ethyl-3-methylimidazolium bis(trifluormethylsulfonyl) imide (EMITFSI) were investigated using the scanning transmission soft X-ray microscopy (STXM) and spectro-ptychography techniques at the Sn M5,4-edge, I M5,4-edge, O K-edge, C K-edge, and N K-edge. The study offers a comprehensive interpretation of the spectral characteristics of main components (C, N, Sn, and I) in Sn-based perovskites through STXM-based techniques and further reveals differences between the perovskite samples with and without adding EMITFSI ionic liquid. The chemical imaging of Sn and I shows that the perovskite sample without ionic liquid has Sn-rich regions in iodine cavities, while the ionic liquid-treated sample exhibits a more homogeneous perovskite phase. Furthermore, the C and N K-edge XANES resonance features support the interaction between the non-volatile ionic liquid and FA+, thus playing a protective role in the formation and stabilization of perovskite phase.

Engineering Stable Lead-Free Tin Halide Perovskite Solar Cells: Lessons from Materials Chemistry.

Substituting toxic lead with tin (Sn) in perovskite solar cells (PSCs) is the most promising route toward the development of high-efficiency lead-free devices. Despite the encouraging efficiencies of Sn-PSCs, they are still yet to surpass 15% and suffer detrimental oxidation of Sn(II) to Sn(IV). Since their first application in 2014, investigations into the properties of Sn-PSCs have contributed to a growing understanding of the mechanisms, both detrimental and complementary to their stability. This review summarizes the evolution of Sn-PSCs, including early developments to the latest state-of-the-art approaches benefitting the stability of devices. The degradation pathways associated with Sn-PSCs are first outlined, followed by describing how composition engineering (A, B site modifications), additive engineering (oxidation prevention), and interface engineering (passivation strategies) can be employed as different avenues to improve the stability of devices. The knowledge about these properties is also not limited to PSCs and also applicable to other types of devices now employing Sn-based perovskite absorber layers. A detailed analysis of the properties and materials chemistry reveals a clear set of design rules for the development of stable Sn-PSCs. Applying the design strategies highlighted in this review will be essential to further improve both the efficiency and stability of Sn-PSCs.

Band gap tailoring with octahedral distortion and bader charge analysis for 2D-Ruddlesden–Popper monolayer tin halide perovskites

Intercalation of large organic spacer cations with inorganic layers of octahedral metal halide cages in 2D-Ruddlesden–Popper (RP) monolayer perovskites (R–NH3)2An−1BnX3n+1 by using a rational design approach has shown structural versatility and energetic stability. A systematic theoretical investigation of the structural, electronic, and mechanical properties was conducted with and without spin-orbit coupling (SOC) under the influence of a range of organic monovalent spacer cations [R–NH3]+ with different inorganic halide anions. This resulted in 12 compositions. Lattice distortion and octahedral tilting provided gradient band gaps that displayed a good linear relationship with equatorial Sn–X–Sn angles in debt of larger halide anions. By fixing halide ions, larger spacer cations reduce the band gap further. The halides function as acceptors, whereas Sn and N function as donors. Intermingled N-atoms of spacer cations incorporate additional charges to axial halide ions of [SnX6]4- with state-of-the-art features of defect tolerance, quantum and dielectric confinement, low effective masses, and high mobility.

Dimensional Tuning in Lead‐Free Tin Halide Perovskite for Solar Cells (Adv. Energy Mater. 13/2023)

Quasi-2D Tin Perovskites As the most promising alternative to lead halide perovskite, tin halide perovskite suffers from the intrinsic Sn(II) instability. Incorporating large-sized organic cations forming quasi-2D structures increases the perovskite stability. For this reason, in article number 2204233, Guixiang Li, Mahmoud H. Aldamasy, Meng Li, and co-workers, discuss and evaluate the characteristics and challenges of quasi-2D tin perovskites, and propose potential research strategies for opening up new opportunities of lead-free tin-based perovskite photovoltaics.

A simulation study of all inorganic lead-free CsSnBr3 tin halide perovskite solar cell

Perovskite solar cells (PSCs) have achieved champion efficiency from 3.8% to 25.2% in a decade. The major issues associated with perovskite solar cells are stability and toxicity. These PSCs quickly degrade in the ambient environment. The use of toxic lead in the hybrid organic–inorganic solar cells makes them unsafe as future technology. Recently, tin-based perovskite solar cells have gained attention as an alternative for resolving the issues of stability and toxicity. Numerical simulations help in finding the possible alternatives and understanding the underlying mechanism to solve the toxicity and stability problem. The present work aims to simulate lead-free perovskite solar cells and optimise the width of each layer. SCAPS_1D simulation software is used here to conduct the study. CsSnBr3 is used as an absorber layer, while SnO2 is used as an electron transport layer, and CuI is used as a hole transport layer. The simulation is conducted at 300 K temperature and AM1.5G solar spectrum. The device achieves a remarkable photovoltaic conversion efficiency of 17.06%, an open-circuit voltage (Voc) of 1.19 V, a current density of 16.94 mA/cm2, and a fill factor of 84.19%. Thus, tin-based halide perovskite paves the way for future environmentally friendly and stable perovskite solar cells.

Rationally designed Dion-Jacobson Tin-halide perovskites with improved phase stability and Inter-layer charge transport by intercalating alkyl cation-ligands

Currently, the development of CsSnI3 perovskite is still greatly hindered by their intrinsic deficiencies, such as their easy phase transformation. To address this issue, we theoretically constructed Dion-Jacobson (DJ) perovskites intercalated by divalent 1,5-pentamethylenediamine (PeDA2+) exhibit significantly enhanced phase stability. However, the carrier mobility is always depressed owing to the charge localization and severe lattice distortion in the presence of spacers among wafers. Thus, the alkyl ligand cations (e.g., ethylenediamine (EDA), 1,3-propanediamine (PDA), 1,4-butanediamine (BDA)) with varying lengths as organic intercalators are examined for optimizing charge transfer. Compared with the other configures, the (PDA)Cs2Sn3I10 exhibits the most significantly improved stability due to the enhanced chemical bonding and faintest structural distortions, as evidenced by computed the formation enthalpy. Formation energy and transition level of tin-vacancy defect further confirm the improved stability and depressed defect-trapping states. Meanwhile, 2D-(PDA)Cs2Sn3I10 exhibit obviously increased electrical conductivity and reduced carrier effective masses, which might benefit the photoelectric conversion of solar cells.

Buried-in interface with two-terminal functional groups for perovskite-based photovoltaic solar cells

Interface plays an important role in perovskite solar cells. Herein, a functional molecular with two-terminal donor groups was deposited between the tin oxide (SnO2) electron transport layer and halide perovskite to induce the perovskite crystal growth and passivate defects at the interface. It is found that isonicotinohydrazide (INHA) can anchor Pb2+ cluster in precursor and promote uniform nucleation, which helps to adjust the crystal growth in perovskite films. As well, more analysis shows that interfacial modification can greatly reduce trap defects and therefore facilitate photogenerated carrier-transferring. The efficient electron transfer and reduced interface traps correlate well with the corresponding fill factors and open-circuit voltages (VOC) of working devices. The resulting perovskite solar cell exhibits striking improvements to reach the champion efficiency of 21.12%. The long-term stability is also significantly enhanced by comparing to the pristine devices. This work highlights the effect of INHA/perovskite interfacial interaction and provides a multi-functional passivation strategy for further perfecting perovskite films.

Oriented Attachment of Tin Halide Perovskites for Photovoltaic Applications

Tin halide perovskites (THPs) are hopeful replacements to toxic Pb-based perovskites in lead-free photovoltaic applications. Nevertheless, the underlying crystallization kinetics mechanism lacks exploration to inform the rational design of high-quality THP films for the fabrication of optoelectronic devices. Here, we reveal a crystal growth kinetic regime for oriented attachment growth of THPs. By introducing 2-phenoxyethylamine bromide (POEBr) to tune the surface energy of different facets of FASnI3 perovskite crystals, highly oriented FASnI3-POEBr perovskite films are obtained. The crystalline films with anisotropic properties can be rationalized through the crystal growth kinetics mechanism called “oriented attachment (OA)”, where two smaller nanocrystals with the same crystallographical orientation combine together to produce a larger nanocrystal. The OA growth kinetics is amenable to reducing the crystal growth rate and consequently allows the formation of dense, smooth, and oriented THP films with fewer defects, delivering an impressive efficiency of over 14%.

Cubic or Not Cubic? Combined Experimental and Computational Investigation of the Short-Range Order of Tin Halide Perovskites.

Tin-based metal halide perovskites with a composition of ASnX3 (where A= MA or FA and X = I or Br) have been investigated by means of X-ray total scattering techniques coupled to pair distribution function (PDF) analysis. These studies revealed that that none of the four perovskites has a cubic symmetry at the local scale and that a degree of increasing distortion is always present, in particular when the cation size is increased, i.e., from MA to FA, and the hardness of the anion is increased, i.e., from Br- to I-. Electronic structure calculations provided good agreement with experimental band gaps for the four perovskites when local dynamical distortions were included in the calculations. The averaged structure obtained from molecular dynamics simulations was consistent with experimental local structures determined via X-ray PDF, thus highlighting the robustness of computational modeling and strengthening the correlation between experimental and computational results.

Performance Enhancement of Lead-Free 2D Tin Halide Perovskite Transistors by Surface Passivation and Its Impact on Non-Volatile Photomemory Characteristics.

Two-dimensional(2D) tin(Sn)-based perovskites have recently received increasing research attention for perovskite transistor application. Although some progress is made, Sn-based perovskites have long suffered from easy oxidation from Sn2+ to Sn4+ , leading to undesirable p-doping and instability. In this study, it is demonstrated that surface passivation by phenethylammonium iodide (PEAI) and 4-fluorophenethylammonium iodide (FPEAI) effectively passivates surface defects in 2Dphenethylammonium tin iodide(PEA2 SnI4 )films, increases the grain size by surface recrystallization, and p-dopes the PEA2 SnI4 film to form a better energy-level alignment with the electrodes and promote charge transport properties. As a result, the passivated devices exhibit better ambient and gate bias stability, improved photo-response, and higher mobility, for example, 2.96 cm2 V-1 s-1 for the FPEAI-passivated films-four times higher than the control film (0.76 cm2 V-1 s-1 ). In addition, these perovskite transistors display non-volatile photomemory characteristics and are used as perovskite-transistor-based memories. Although the reduction of surface defects in perovskite films results in reduced charge retention time due to lower trap density, these passivated devices with better photoresponse and air stability show promise for future photomemory applications.