Degradation mechanism of hybrid tin-based perovskite solar cells and the critical role of tin (IV) iodide

Self-assembled monolayers for tin perovskite solar cells: challenges and opportunities

Large-scale implementation of emerging halide perovskite solar cells (PSCs) has been restrained by environmental and health concerns stemming from the use of lead in their composition. In contrast, tin perovskite solar cells (TPSCs) have been widely recognized as viable alternatives owing to their ideal optical band gap, high carrier mobility and excellent optoelectronic properties. However, TPSCs encounter significant open-circuit voltage (Voc) deficits due to the spontaneous oxidation of Sn2+ and uncontrolled crystallization process. Hence, self-assembled monolayers (SAMs) are now explored as a solution to optimize the perovskite/transport layer interface and improve Voc. Despite the potential advantages and wide applications of SAMs in other optoelectronic devices, their application in TPSCs is relatively scarce. In this review, we elucidated the working mechanism of SAMs in improving device efficiency, summarized the recent progresses, and outlined the challenges in their application in TPSCs. We also discussed strategies for leveraging SAMs to mitigate the Voc deficit in TPSCs. We hope that this review would offer a unique perspective for the ongoing research endeavors focused on the application of SAMs in TPSCs.

Efficient Sn-Pb Perovskite Solar Cells Through Inhibiting Hole Accumulation

Sn-Pb perovskite solar cells (PSCs) own the highest theoretical efficiency due to their ideal bandgap. However, the efficiency of Sn-Pb PSCs remains 22-23% at present, which is much lower than Pb-based PSCs. One key reason lies in the Sn2+ oxidation issue. Here, this study demonstrates that apart from well-known chemical environmental oxidation, photo-generated holes and their accumulation are also a critical factor for Sn2+ oxidation in Sn-Pb PSCs. To address this issue, a non-planar hole transport layer (HTL) of P3CT/Me-4PACz is designed through solution micelle regulation. P3CT/Me-4PACz will form a 3D HTL film with a spike-like structure penetrating Sn-Pb perovskite bulk to accelerate hole extraction, thus inhibiting holes accumulation and Sn2+ oxidation. Resulted Sn-Pb PSCs exhibit the highest efficiency of over 24% with good operational stability, retaining 82% of initial efficiency after continuous MPP tracking for 1000 h at an elevated temperature of 55 °C.

All-Inorganic Tin-Containing Perovskite Solar Cells: An Emerging Eco-Friendly Photovoltaic Technology

All-inorganic tin (Sn)-containing perovskites have emerged as highly promising photovoltaic materials for single-junction and tandem perovskite solar cells (PSCs), owing to their reduced toxicity, optimal narrow bandgap, and superior thermal stability. Since their initial exploration in 2012, significant advancements have been achieved, with the highest efficiencies of single-junction and tandem devices now surpassing 17% and 22%, respectively. Nevertheless, the intrinsic challenges associated with the oxidation susceptibility of Sn2+ and the uncontrolled crystallization dynamics impede their further development. Addressing these issues necessitates a comprehensive and systematic understanding of the degradation mechanisms inherent to all-inorganic Sn-containing perovskites, as well as the development of effective mitigation strategies. This review provides a detailed overview of the research progress in all-inorganic Sn-containing PSCs, with a particular focus on the basic properties and degradation pathways of both pristine Sn and mixed Sn-Pb perovskites. Furthermore, various strategies to improve the efficiency and stability of Sn-containing PSCs are thoroughly discussed. Finally, the existing challenges and perspectives are provided for further improving the photovoltaic performance of eco-friendly PSCs.

Nucleation-Layer Assisted Quasi-2D Ruddlesden-Popper Tin Perovskite Solar Cells With High Oxygen Stability

Tin (Sn)-based perovskite solar cells (PSCs) are extremely vulnerable to oxygen. Nevertheless, mechanism understanding and fundamental strategies to achieve oxygen-stable Sn-based PSCs are lacking. Here a nucleation-layer assisted (NLA) strategy by forming nucleation layer at the interface of hole transport layer and perovskite to attain highly oxygen-stable quasi-2D Ruddlesden-Popper (RP) Sn-based PSCs is reported. The formation process of nucleation layer consists of washing off the prepared perovskite film and annealing the residue on the substrate, which produces a new substrate for perovskite film fabrication. Such nucleation layer can transform the subsequently deposited perovskite film from a small-n-value dominated wide phase distribution with random crystal orientation into an intermediate-n-value dominated narrow phase distribution with vertical crystal orientation. This nucleation layer also improves the perovskite film morphology with highly coadjacent flake-like grains, leading to reduced grain boundaries and pinholes. The resultant NLA perovskite film shows more efficient carrier transport capability, lower exciton-binding energy, weakened electron-phonon coupling, and significantly decreased oxygen diffusion rate upon oxygen exposure. Consequently, a quasi-2D RP Sn-based PSC with a champion efficiency of 11.18% is obtained. The unencapsulated device preserves 95% of its initial efficiency after a 2700-h oxygen aging test, creating a record oxygen stability for Sn-based PSCs.

Construction of hydrophobic microenvironment on Sn0@SBA-15 for efficient and stable iodine gas capture

Tin-based materials are promising for iodine capture. However, they suffer from the instability of adsorption product SnI4 that is easily hydrolyzed even in atmospheric environment due to the presence of moisture. Herein, we report a strategy of constructing the hydrophobic microenvironment on Sn0@SBA-15 materials, which isolates moisture and subsequently stabilizes SnI4. Hydrophobic Sn0@SBA-15 materials (P-Sn0@SBA-15) were fabricated by polymethylhydrosiloxane (PHMS) modification and applied for iodine capture. The obtained P-Sn0@SBA-15 exhibited a record high iodine adsorption capacity (2599 mg/g) among inorganic adsorbents. The dominant adsorption mechanism was found that Sn0 reacted with I2 to form SnI4. Remarkably, SnI4 in P-Sn0@SBA-15 was stable up to 3 months exposure to humid atmosphere, while almost all SnI4 in Sn0@SBA-15 was hydrolyzed. The obtained P-Sn0@SBA-15 could be added to the list of iodine adsorbents due to its excellent adsorption capacity and stability. Moreover, the facile strategy could provide reference for the development of other functional materials.

Powder Methodology-An Effective Way to Suppress Sn2+ Oxidation in Narrow Bandgap Pb-Sn Perovskite

Lead-tin halide perovskites are of significant merits due to their suitability for tandem solar cell fabrication and for lowering the environmental impact. However, the substantial disparity in the crystallization of tin- and lead-based perovskites, coupled with the tendency of Sn2+ to oxidize rapidly, poses hurdles and rise in defect concentration. Here, the study proposes a cost-effective and facile route to synthesize lead-tin halide perovskite microcrystals. The perovskite formulation and the thin films deposited from lead-tin halide perovskite microcrystal exhibit an improved stability of Sn2+ against environmental humidity conditions compared to their precursor-based counterparts. The device fabricated with FAPb0.5Sn0.5I3 microcrystal measures a power conversion efficiency of 18.55% with an open-circuit voltage of 800 mV, coupled with low-cost precursors and lead mitigation protocols.

Caesium-Iodide-Assisted Synthesis of High-Quality, Stable, and Robust Lead-Free Perovskite Quantum Dots

The poor morphology, and susceptibility to oxidation of tin-based perovskite quantum dots (TQDs) have posed significant challenges, limiting their application potential. This study presents a straightforward method for synthesizing high-quality CsSnI3-based perovskite quantum dots (TQDs) by incorporating a mixed Cs source of Cs2CO3 and CsI. The addition of CsI increased the I:Sn ratio while maintaining Sn:Cs, resulting in TQDs with smaller size and improved uniformity. X-ray photoelectron spectroscopy (XPS), and Nuclear magnetic resonance (NMR) analyses confirmed enhanced crystallinity, photoluminescence intensity, and antioxidation ability of CsI-TQDs. Remarkably, these TQDs exhibit exceptional stability, enduring over 1 h in air and more than 24 h before complete oxidation, surpassing the previously reported longest lifetime in air for TQDs with conventional oleic acid (OA) and oleylamine (OAm) ligands. Furthermore, these TQD films retain robustness after ligand exchange with methyl acetate (MeOAc) and formamidinium iodide (FAI), representing the first successful short-ligand exchange of TQDs and enabling further electronic device applications. These findings suggest that CsI in the Cs source plays a crucial role in facilitating the formation of surface complexes, regulating TQD growth and suppressing iodine vacancies.

Dual Oxidation Suppression in Lead-Free Perovskites for Low-Threshold and Long-Lifespan Lasing

Low lasing threshold and long-term operational stability are essential in advancing cost-effective, efficient lead-free (tin) halide perovskite lasers. However, the rapid crystallization of tin perovskites and oxidation of Sn2+ lead to substantial amounts of lattice defects, detrimental to laser performance enhancement. Herein, a dual oxidation suppression strategy is developed to suppress the oxidation of Sn2+ 2D tin halide perovskites, i.e., adopting an oxygen-free two-step growth to enhance the crystal quality and incorporating electron-donating biuret molecules to coordinate with Sn2+ during the crystal growth, which led to the substantial reduction of lasing threshold to <1 µJ cm- 2 in (PEA)2MASn2I7. This represents the lowest value in lead-free perovskite nanolasers and approximately one order of magnitude lower than those previously reported for tin-based nanolasers. Investigations into the spontaneous photoluminescence (PL) and stimulated lasing emission revealed that 2D tin perovskites exhibited superior photostability and lasing stability compared to their lead counterparts. Specifically, the lasing intensity of (PEA)2MA2Sn3I10 constantly increased by >300% under optical pumping and the lasing threshold decreased by ≈17%, which is not observed in their lead counterparts. The findings highlight the prospect of 2D tin halide perovskites as lead-free gain materials and cavities for solution-processed nanolasers with low lasing thresholds and exceptional stability.

Competitive-Coordination-Induced Crystallization Regulation for Efficient and Stable Sn-Pb Perovskite Solar Cells

The unbalanced crystallization rate between Sn- and Pb-based perovskites leads to their heterogeneous distribution and inferior quality of Sn-Pb perovskite films. The promising strategy of selective molecular interaction would balance the crystallization rate. However, the deeper selectivity mechanism needs to be considered, particularly in terms of the entire coordination reaction in the perovskite precursor solution. Herein, we take advantage of thermodynamics and molecular orbital theory to reveal the competitive coordination of additive, i.e., methyl 5-aminolevulinate hydrochloride (5-AH), with SnI2 and PbI2. The SnI2 competes with PbI2 in coordinating with 5-AH to form the thermodynamically favored SnI2-5-AH adducts with stronger SnI2-Cl-, thereby mediating the crystallization rate of the Sn- and Pb-based perovskite. Such crystallization regulation improves the composition uniformity and crystallization quality, which effectively suppresses nonradiative recombination. Additionally, the strong interaction between Sn2+ and 5-AH as well as reductive grain boundaries inhibits the oxidation of Sn2+. Therefore, the optimal devices with 5-AH exhibit an improved PCE of 23.76% with a high voltage of 0.885 V and long-term stability.

Reaction-Diffusion and Crystallization Kinetics Modulation of Two-Step Deposited Tin-Based Perovskite Film via Reducing Atmosphere

The two-step deposition method effectively mitigates the efficiency decline observed in tin-based perovskite solar cells (TPVSCs) with increasing cell area, stemming from film in-homogeneity. However, the high solubility of SnI2 in the conventionally used solvent isopropyl alcohol, coupled with the absence of effective modulation of reaction-diffusion process, results in inadequate film coverage and conversion. In this study, we introduce formic acid as the second-step solvent and introduce dithiothreitol (DTT) to regulate reaction-diffusion/crystallization kinetics meticulously. Moreover, this research underscores a fundamental principle that the suitable binding energy ranging from -1.38 to -10.10 kcal mol-1 between ligands and Sn2+ significantly enhances the effectiveness of two-step crystallization control. Notably, a uniform perovskite film is achieved on large-scale substrate, and TPVSCs processed with DTT exhibit the highest efficiencies of 12.68 % for 0.04 cm2 device and 11.30 % for 1 cm2 device among tin-based perovskite devices in two-step sequential deposition method, even in the absence of dimethyl sulfoxide. This study lays the groundwork for the potential scale-up development of lead-free perovskite solar cells.

Improved Crystallinity and Defect Passivation for Formamidinium Tin Iodide-Based Perovskite Light-Emitting Diodes

The toxicity of lead (Pb) presents a critical challenge for the application of perovskite optoelectronics. In tin (Sn) perovskite, Sn2+ is easily oxidized to Sn4+ during the crystallization process. The uncontrollable oxidation process affects the crystallinity of perovskite films and leads to nonradiative traps within the films, resulting in poor device performance. Herein, we improve the efficiency of formamidinium tin iodide (FASnI3)-based perovskite LEDs (PeLEDs) through the inclusion of phenyl-thioure (PTC), which enhances crystallinity and suppresses oxidation of the Sn perovskite emitters. We achieve a high-performance near-infrared FASnI3-based PeLED with a peak external quantum efficiency (EQE) of 6.4% and a maximum radiance of 117 W sr-1 m-2. The devices exhibit operational lifetimes (T50) of ∼12.4 h under a constant current density of 10 mA cm-2, representing some of the most stable FASnI3-based PeLEDs. Our work explores a pathway for regulating crystallinity, inhibiting oxidation, and passivating defects in lead-free Sn-based PeLEDs.

Unravelling the Role of Indium in Enhancing the Stability of Mixed Tin-Lead Perovskite Solar Cells

Tin-lead metal halide perovskites show promise as light-absorbing materials with a tunable band gap (1.2-1.4 eV) for efficient perovskite solar cells (PSCs) with less toxicity. However, the instability of the tin(II) ionic state limits the lifetime of their PSCs, which reduces their real-world feasibility. Herein, indium(III) iodide (InI3) is used to modulate the Sn-Pb perovskite crystal lattice to improve the stability of the film, in addition to improving the photovoltaic performance of the corresponding PSC devices. It is found that the indium cation shows an ability to substitute tin(II) vacancies in the perovskite crystal structure, resulting in a more stable structure. The InI3-modified films exhibit enhanced surface morphology and crystallinity, reduced trap state density, and nonradiative recombination in the solar cells expressed in improved device performance of the Sn-Pb-based PSCs from 17.2 to 18.1% and an enhancement in the stability of the perovskite during exposure to elevated temperature and humid atmospheric air.

Revealing the role of intrinsic point defects in the stability of halide double perovskite Cs2AgBiBr6

An ab initio study of halide double perovskite (HDP) Cs2AgBiBr6 is presented. The antisites Br-2Cs and Bi+2Cs are found to be dominant acceptor- and donor-type defects, while the BiCs defect exhibits a deep transition level to form electron traps and Br migration has the lowest activation barrier. Our work provides a fundamental understanding of defect physics and chemistry in HDPs, highlighting that the Br-rich condition is preferable for improving the photovoltaic performance and chemical stability.

Unveiling Popular PEDOT:PSS-Derived Composition Segregation Effect in Tin-Lead Mixed Perovskite Solar Cells and Elimination

As the most popular hole-transport material for promising tin-lead mixed perovskite (TLP) solar cells, poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) would cause the composition segregation of TLP, besides exacerbating degradation and parasitic absorption reported previously. However, the segregation phenomenon is now crucial but was rarely discussed previously, and the mechanism behind it was hardly investigated. In this work, we reveal unambiguously that PSS with a sulfonic acid group in PEDOT:PSS has the propensity to coordinate Sn prior to Pb and causes the uneven nucleation at the surface of PEDOT:PSS, further affecting the growth of the TLP film. This resulted in severe tin enrichment, and voids frequently occurred at the buried interfacial layer; herein, the Sn/Pb distribution was uneven through the TLP film. To address this concern, we designed 4-(10H-phenoxazin-10-yl)butyl)phosphonic acid (PXZPA) to exclude that negative effect. For the Cs0.1FA0.7MA0.2Sn0.3Pb0.7I3 TLP material with a bandgap of 1.30 eV, the defect density declined obviously from 1.33 × 1016 cm-3 to 5.78 × 1015 cm-3, and the champion device conversion efficiency surged remarkably from 17.27% to 22.43%.

Buried hole-selective interface engineering for high-efficiency tin-lead perovskite solar cells with enhanced interfacial chemical stability

Mixed Sn-Pb perovskites are attracting significant attention due to their narrow bandgap and consequent potential for all-perovskite tandem solar cells. However, the conventional hole transport materials can lead to band misalignment or induce degradation at the buried interface of perovskite. Here we designed a self-assembled material 4-(9H-carbozol-9-yl)phenylboronic acid (4PBA) for the surface modification of the substrate as the hole-selective contact. It incorporates an electron-rich carbazole group and conjugated phenyl group, which contribute to a substantial interfacial dipole moment and tune the substrate's energy levels for better alignment with the Sn-Pb perovskite energy levels, thereby promoting hole extraction. Meanwhile, enhanced perovskite crystallization and improved contact at bottom of the perovskite minimized defects within perovskite bulk and at the buried interface, suppressing non-radiative recombination. Consequently, Sn-Pb perovskite solar cells using 4PBA achieved efficiencies of up to 23.45%. Remarkably, the 4PBA layer provided superior interfacial chemical stability, and effectively mitigated device degradation. Unencapsulated devices retained 93.5% of their initial efficiency after 2000 h of shelf storage.

A Natural Antioxidant Organic Material Modifying the Buried Interface To Regulate the Photovoltaic Performance and Stability of Pure Tin-Based Perovskite Solar Cells

Despite showing great potential in lead-free green energy, tin-based perovskite materials still face challenges such as inherent material instability and energy level misalignment with the hole transport layer (HTL), which limits the advancement of tin-based perovskite solar cells (Sn-PSCs). In this work, a natural antioxidant organic small molecule, thiolactic acid (TA), is used to modify the interface between PEDOT:PSS and the tin-based perovskite film. The TA molecule can cross-link to form a network polymer and regulate the microstructure and photoelectrical characteristics of PEDOT:PSS. Meanwhile, TA contains C═O and C─S groups, which can interact with Sn2+ to inhibit its oxidation. Moreover, the introduction of TA interfacial modification effectively improves the morphology of the perovskite film, suppresses interfacial charge recombination, and promotes carrier transport. Thus, TA-modified Sn-PSCs achieve a champion power conversion efficiency of 9.03%, surpassing 6.92% of the control PSCs. Even after being stored for 1000 h in a nitrogen atmosphere, the unencapsulated devices with TA modification still maintain 95.4% of their original PCE, compared to only 66.5% of the control devices. This study demonstrates the significance of the PEDOT:PSS/tin-perovskite interfacial modification on the efficiency and stability of Sn-PSCs.

Ferromagnetic Nickel as a Sustainable Reducing Agent for Tin-Lead Mixed Perovskite in Single-Junction and Tandem Solar Cells

Narrow-bandgap (NBG) Sn-Pb mixed perovskite solar cells (PSCs) represent a promising solution for surpassing the radiative efficiency of single-junction solar cells. The unique bandgap tunability of halide perovskites enables optimal tandem configurations of wide-bandgap (WBG) and NBG subcells. However, these devices are limited by the susceptibility of Sn2+ in the NBG bottom cell to being oxidized to Sn4+, creating detrimental Sn vacancies. Herein, a novel approach that replaces Sn particles with Ni particles is introduced as the reducing agent for Sn-Pb mixed perovskite precursor solutions. The ferromagnetic properties of Ni enable simple magnetic filtration, eliminating the filtration issues associated with Sn particles. Ni particles can be reused up to five times without significantly affecting the PSC's performance. Additionally, Ni effectively mitigates the oxidation of Sn2+ due to its low reduction potential (-0.23 V), thereby enhancing device performance. Single-junction Sn-Pb mixed PSCs prepared using Ni achieve a power-conversion efficiency (PCE) of 22.29%, retaining over 90% of their initial efficiency after 1250 h. Furthermore, Ni-based all-perovskite tandem solar cells combining 1.77 eV WBG top cells with 1.25 eV NBG bottom cells achieve a remarkable PCE of 28.13%. Thus, the proposed strategy can facilitate the commercialization of all-perovskite tandem devices.

Salutary impact of spontaneous oxidation in CH3NH3SnI3 on CZTS-based solar cell

From the time of discovery, CH3NH3SnI3 has been a promising candidate in photovoltaics due to its outstanding optoelectronic properties. However, stabilization was not easy to achieve in CH3NH3SnI3-based solar cells. Because CH3NH3SnI3 was used as an absorber, its naturally-occurring self-doping property spontaneously modified band alignment, which increased carrier recombination and decreased the efficiency of solar cell gradually. In this paper, for the first time, we have presented detailed study on use of CH3NH3SnI3 as a hole transport layer in prototype solar cell having configuration: CH3NH3SnI3/CZTS/CdS/ZnO/AZO, using SCAPS software. To understand the effect of spontaneous self-doping property of CH3NH3SnI3 on solar cell performance, the analysis of variation in solar cell performance parameters, band alignment conduction band, valance band, Fermi levels, charge density, current density, conductance, capacitance and recombination rate was performed as a function of increasing CH3NH3SnI3 carrier concentration. It was found that, when used as an hole transport layer, the inherent self-doping property of CH3NH3SnI3 became a helpful trait to increase hole extraction and spontaneously enhanced our device efficiency. Thus, the inherent self-doping property of CH3NH3SnI3 transformed from curse to boon when we leveraged CH3NH3SnI3 as an hole transport layer in our solar cell device.

The Effect of Antisolvent Treatment on the Growth of 2D/3D Tin Perovskite Films for Solar Cells

Antisolvent treatment is used in the fabrication of perovskite films to control grain growth during spin coating. We study widely incorporated aromatic hydrocarbons and aprotic ethers, discussing the origin of their performance differences in 2D/3D Sn perovskite (PEA0.2FA0.8SnI3) solar cells. Among the antisolvents that we screen, diisopropyl ether yields the highest power conversion efficiency in solar cells. We use a combination of optical and structural characterization techniques to reveal that this improved performance originates from a higher concentration of 2D phase, distributed evenly throughout the 2D/3D Sn perovskite film, leading to better crystallinity. This redistribution of the 2D phase, as a result of diisopropyl ether antisolvent treatment, has the combined effect of decreasing the Sn4+ defect density and background hole density, leading to devices with improved open-circuit voltage, short-circuit current, and power conversion efficiency.

Mitigation of Self-p-Doping and Off-Centering Effect in Tin Perovskite via Strontium Doping

Tin-based perovskite solar cells offer a less toxic alternative to their lead-based counterparts. Despite their promising optoelectronic properties, their performances still lag behind, with the highest power conversion efficiencies reaching around 15%. This efficiency limitation arises primarily from electronic defects leading to self-p-doping and stereochemical activity of the Sn(II) ion, which distorts the atomic arrangement in the material. In this study, we investigate the effect of strontium doping in tin-based perovskite on the distortion of the material's structure and its optoelectronic properties. Using a combination of Density Functional Theory calculations and experiments, we demonstrate that strontium doping reduces p-doping and structural strain. This approach improves the efficiency from 6.3% in undoped devices to 7.5% in doped devices without relying on dimethyl sulfoxide, a harmful solvent for tin-based perovskites. This method could enable precise control of tin off-centering and self-p-doping, advancing the development of efficient and stable tin perovskite solar cells.

Unveiling the nexus between irradiation and phase reconstruction in tin-lead perovskite solar cells

Tin-lead perovskites provide an ideal bandgap for narrow-bandgap perovskites in all-perovskite tandem solar cells, fundamentally improving power conversion efficiency. However, light-induced degradation in ambient air is a major issue that can hinder the long-term operational stability of these devices. Understanding the specifics of what occurs during this pathway provides the direction for improving device stability. In this study, we investigate the long-term stability problem of tin-lead perovskites under irradiation, counterintuitively discovering an irreversible phase reconstruction process. In-situ photoluminescence spectroscopy is used to monitor the reconstruction process, which involves the reaction of oxygen with photoexcited electrons to form superoxide. It is proposed that Pb-rich regions appear on the surface after Sn2+ oxidation, and these Pb-rich regions are reconstituted from the yellow phase of formamidinium lead iodide to the black phase with prolonged irradiation. This study highlights the phase reconstruction process during the degradation of tin-lead perovskites, providing valuable insights into the superoxide degradation mechanism and guiding further stability improvements for narrow-bandgap tin-lead perovskites and tandem solar cells.

Sustainability pathways for perovskite photovoltaics

Solar energy is the fastest-growing source of electricity generation globally. As deployment increases, photovoltaic (PV) panels need to be produced sustainably. Therefore, the resource utilization rate and the rate at which those resources become available in the environment must be in equilibrium while maintaining the well-being of people and nature. Metal halide perovskite (MHP) semiconductors could revolutionize PV technology due to high efficiency, readily available/accessible materials and low-cost production. Here we outline how MHP-PV panels could scale a sustainable supply chain while appreciably contributing to a global renewable energy transition. We evaluate the critical material concerns, embodied energy, carbon impacts and circular supply chain processes of MHP-PVs. The research community is in an influential position to prioritize research efforts in reliability, recycling and remanufacturing to make MHP-PVs one of the most sustainable energy sources on the market.

Enhancing the Efficiency and Stability of Tin-Lead Perovskite Solar Cells via Sodium Hydroxide Dedoping of PEDOT:PSS

Tin-lead (Sn-Pb) perovskite solar cells (PSCs) have gained interest as candidates for the bottom cell of all-perovskite tandem solar cells due to their broad absorption of the solar spectrum. A notable challenge arises from the prevalent use of the hole transport layer, PEDOT:PSS, known for its inherently high doping level. This high doping level can lead to interfacial recombination, imposing a significant limitation on efficiency. Herein, NaOH is used to dedope PEDOT:PSS, with the aim of enhancing the efficiency of Sn-Pb PSCs. Secondary ion mass spectrometer profiles indicate that sodium ions diffuse into the perovskite layer, improving its crystallinity and enlarging its grains. Comprehensive evaluations, including photoluminescence and nanosecond transient absorption spectroscopy, confirm that dedoping significantly reduces interfacial recombination, resulting in an open-circuit voltage as high as 0.90 V. Additionally, dedoping PEDOT:PSS leads to increased shunt resistance and high fill factor up to 0.81. As a result of these improvements, the power conversion efficiency is enhanced from 19.7% to 22.6%. Utilizing NaOH to dedope PEDOT:PSS also transitions its nature from acidic to basic, enhancing stability and exhibiting less than a 7% power conversion efficiency loss after 1176 h of storage in N2 atmosphere.

Inkjet-Printed FASn1-xPbxI3-Based Perovskite Solar Cells

Metal halide perovskite solar cells (PSCs) have gained significant attention in thin-film photovoltaic research for their high power conversion efficiency (PCE) and facile fabrication processes. This study presents the use of inkjet printing to fabricate thin films of combinatorial mixed formamidinium tin-lead perovskites and evaluates their layer quality and device performance. Our findings demonstrate that incorporating Pb up to 50% into FASnI3 films enhances lattice stability. The investigation focused on optimizing the composition ratio for improved photovoltaic performance with FASn0.5Pb0.5I3-based PSCs achieving the highest PCE of 10.26%. Additionally, these cells exhibited an absorption spectrum extending beyond 1000 nm, corresponding to a 1.25 eV bandgap. The results suggest that inkjet printing can effectively enhance the efficiency of tin-lead-based PSCs, supporting scalability in device manufacturing.

Targeted elimination of tetravalent-Sn-induced defects for enhanced efficiency and stability in lead-free NIR-II perovskite LEDs

Eco-friendly Sn-based perovskites show significant potential for high-performance second near-infrared window light-emitting diodes (900 nm - 1700 nm). Nevertheless, achieving efficient and stable Sn-based perovskite second near-infrared window light-emitting diodes remains challenging due to the propensity of Sn2+ to oxidize, resulting in detrimental Sn4+-induced defects and compromised device performance. Here, we present a targeted strategy to eliminate Sn4+-induced defects through moisture-triggered hydrolysis of tin tetrahalide, without degrading Sn2+ in the CsSnI3 film. During the moisture treatment, tin tetrahalide is selectively hydrolyzed to Sn(OH)4, which provides sustained protection. As a result, we successfully fabricate second near-infrared window light-emitting diodes emitting at 945 nm, achieving a performance breakthrough with an external quantum efficiency of 7.6% and an operational lifetime reaching 82.6 h.

Metastable Oxygen-Induced Light-Enhanced Doping in Mixed Sn-Pb Halide Perovskites

Mixed Sn-Pb halide perovskites are promising absorber materials for solar cells due to the possibility of tuning the bandgap energy down to 1.2-1.3 eV. However, tin-containing perovskites are susceptible to oxidation affecting the optoelectronic properties. In this work, we investigated qualitatively and quantitatively metastable oxygen-induced doping in isolated ASnxPb1-xI3 (where A is methylammonium or a mixture of formamidinium and cesium) perovskite thin films by means of microwave conductivity, structural and optical characterization techniques. We observe that longer oxygen exposure times lead to progressively higher dark conductivities, which slowly decay back to their original levels over days. Here oxygen acts as an electron acceptor, leading to tin oxidation from Sn2+ to Sn4+ and creation of free holes. The metastable oxygen-induced doping is enhanced by exposing the perovskite simultaneously to oxygen and light. Next, we show that doping not only leads to the reduction in the photoconductivity signal but also induces long-term effects even after loss of doping, which is thought to derive from consecutive oxidation reactions leading to the formation of defect states. On prolonged exposure to oxygen and light, optical and structural changes can be observed and related to the formation of SnOx and loss of iodide near the surface. Our work highlights that even a short-term exposure to oxygen immediately impairs the charge carrier dynamics of the perovskite, while structural perovskite degradation is only noticeable upon long-term exposure and accumulation of oxidation products. Hence, for efficient solar cells, exposure of mixed Sn-Pb perovskites to oxygen during production and operation should be rigorously blocked.

Overcoming the Open-Circuit Voltage Losses in Narrow Bandgap Perovskites for All-Perovskite Tandem Solar Cells

Narrow-bandgap (NBG) perovskite solar cells based on tin-lead mixed perovskite absorbers suffer from significant open-circuit voltage (V OC) losses due primarily to a high defect density and charge carrier recombination at the device interfaces. In this study, the V OC losses in NBG perovskite single junction cells (E g = 1.21 eV) are addressed. The optimized NBG subcell is then used to fabricate highly efficient all-perovskite tandem solar cells (TSCs). The improvement in the V OC is achieved via the addition of a thin poly(triarylamine) interlayer between the poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS)-based hole transport layer (HTL) and the NBG perovskite. The optimal bilayer HTL results in a champion power conversion efficiency (PCE) of 20.3%, compared to 17.8% of the PEDOT:PSS-based control device. The V OC improvement of the single-junction NBG cell is also successfully transferred to all-perovskite TSC, resulting in a high V OC of 2.00 V and a PCE of 25.1%.

Suppressing Hole Accumulation Through Sub-Nanometer Dipole Interfaces in Hybrid Perovskite/Organic Solar Cells for Boosting Near-Infrared Photon Harvesting

The potential of hybrid perovskite/organic solar cells (HSCs) is increasingly recognized owing to their advantageous characteristics, including straightforward fabrication, broad-spectrum photon absorption, and minimal open-circuit voltage (VOC) loss. Nonetheless, a key bottleneck for efficiency improvement is the energy level mismatch at the perovskite/bulk-heterojunction (BHJ) interface, leading to charge accumulation. In this study, it is demonstrated that introducing a uniform sub-nanometer dipole layer formed of B3PyMPM onto the perovskite surface effectively reduces the 0.24 eV energy band offset between the perovskite and the donor of BHJ. This strategic modification suppresses the charge recombination loss, resulting in a noticeable 30 mV increase in the VOC and a balanced carrier transport, accompanied by a 5.0% increase in the fill factor. Consequently, HSCs that achieve power conversion efficiency of 24.0% is developed, a new record for Pb-based HSCs with a remarkable increase in the short-circuit current of 4.9 mA cm-2, attributed to enhanced near-infrared photon harvesting.

Multi-Functional Silole Hole Transport Layer for Efficient and Stable Lead-Tin Perovskite and Tandem Solar Cells

Despite high theoretical efficiencies and rapid improvements in performance, high-efficiency ≈1.2 eV mixed Sn-Pb perovskite solar cells (PSCs) generally rely on poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT: PSS) as the hole transport layer (HTL); a material that is considered to be a bottleneck for long-term stability due to its acidity and hygroscopic nature. Seeking to replace PEDOT: PSS with an alternative HTL with improved atmospheric and thermal stability, herein, a silole derivative (Silole-COOH) tuned with optimal electronic properties and efficient carrier transport by incorporating a carboxyl functional group is designed, which results in an optimal band alignment for hole extraction from Sn-Pb perovskites and robust air and thermal stability. Thin films composed of the Silole-COOH exhibit superior conductivity and carrier mobility compared to PEDOT: PSS, in addition to reduced nonradiative quasi-Fermi-level splitting losses at the HTL/perovskite interface and improved quality of Sn-Pb perovskite. Replacement of PEDOT: PSS with Silole-COOH leads to 23.2%-efficient single-junction Sn-Pb PSCs, 25.8%-efficient all-perovskite tandems, and long operating stability in ambient air.

Molecularly Engineered Alicyclic Organic Spacers for 2D/3D Hybrid Tin-based Perovskite Solar Cells

The high defect density and inferior crystallinity remain great hurdles for developing highly efficient and stable Sn-based perovskite solar cells (PSCs). 2D/3D heterostructures show strong potential to overcome these bottlenecks; however, a limited diversity of organic spacers has hindered further improvement. Herein, a novel alicyclic organic spacer, morpholinium iodide (MPI), is reported for developing structurally stabilized 2D/3D perovskite. Introducing a secondary ammonium and ether group to alicyclic spacers in 2D perovskite enhances its rigidity, which leads to increased hydrogen bonding and intermolecular interaction within 2D perovskite. These strengthened interactions facilitate the formation of highly oriented 2D/3D perovskite with low structural disorder, which leads to effective passivation of Sn and I defects. Consequently, the MP-based PSCs achieved a power conversion efficiency (PCE) of 12.04% with superior operational and oxidative stability. This work presents new insight into the design of organic spacers for highly efficient and stable Sn-based PSCs.

Innovative Materials for High-Performance Tin-Based Perovskite Solar Cells: A Review

With the rapid development of lead-based perovskite solar cells, tin-based perovskite solar cells are emerging as a non-toxic alternative. Material engineering has been an effective approach for the fabrication of efficient perovskite solar cells. This paper summarizes the novel materials used in tin-based perovskite solar cells over the past few years and analyzes the roles of various materials in tin-based devices. It is found that self-assembling materials and fullerene derivatives have shown remarkable performance in tin-based perovskite solar cells. Finally, this article discusses design strategies for new materials, providing constructive suggestions for the development of innovative materials in the future.

Lead-Free Perovskite Light-Emitting Diodes

Metal halide perovskites have been identified as a promising class of materials for light-emitting applications. The development of lead-based perovskite light-emitting diodes (PeLEDs) has led to substantial improvements, with external quantum efficiencies (EQEs) now surpassing 30% and operational lifetimes comparable to those of organic LEDs (OLEDs). However, the concern over the potential toxicity of lead has motivated a search for alternative materials that are both eco-friendly and possess excellent optoelectronic properties, with lead-free perovskites emerging as a strong contender. In this review, the properties of various lead-free perovskite emitters are analyzed, with a particular emphasis on the more well-reported tin-based variants. Recent progress in enhancing device efficiencies through refined crystallization processes and the optimization of device configurations is also discussed. Additionally, the remaining challenges are examined, and propose strategies that may lead to stable device operation. Looking forward, the potential future developments for lead-free PeLEDs are considered, including the extension of spectral range, the adoption of more eco-friendly deposition techniques, and the exploration of alternative materials.

A first-principles study of organic Lewis bases for passivating tin-based perovskite solar cells

Tin-based perovskite solar cells (PSCs) are potential light absorbers for solar cell applications since they are less toxic compared to commonly used lead-based alternatives. Retaining the less stable Sn2+ state is key to improving the efficiency of tin-based PSCs. Organic Lewis base molecules have demonstrated potential to achieve this purpose. However, the critical factors influencing the performance of Lewis bases are largely unknown. In this study, we applied density functional theory (DFT) to investigate seven Lewis base materials, including methanol (MeOH), dimethyl ether (DME), ethyl methyl ether (EME), methyl acetate (MeOAc), methyl ammonium (MA), methyl sulfonic acid (MSA), and methyl phosphonic acid (MPA). Our results show that the effectiveness of passivation is linked to the gap between the HOMO and the LUMO (Egap). These findings provide theoretical guidance to screen Lewis base additives for enhancing energy conversion efficiencies of tin-based PSCs.

Homogenizing The Low-Dimensional Phases for Stable 2D-3D Tin Perovskite Solar Cells

2D-3D tin-based perovskites are considered as promising candidates for achieving efficient lead-free perovskite solar cells (PSCs). However, the existence of multiple low-dimensional phases formed during the film preparation hinders the efficient transport of charge carriers. In addition, the non-homogeneous distribution of low-dimensional phases leads to lattice distortion and increases the defect density, which are undesirable for the stability of tin-based PSCs. Here, mixed spacer cations [diethylamine (DEA+) and phenethylamine (PEA+)] are introduced into tin perovskite films to modulate the distribution of the 2D phases. It is found that compared to the film with only PEA+, the combination of DEA+ and PEA+ favors the formation of homogeneous low-dimensional perovskite phases with three octahedral monolayers (n = 3), especially near the bottom interface between perovskite and hole transport layer. The homogenization of 2D phases help improve the film quality with reduced lattice distortion and released strain. With these merits, the tin PSC shows significantly improved stability with 94% of its initial efficiency retained after storing in a nitrogen atmosphere for over 4600 h, and over 80% efficiency maintained after continuous illumination for 400 h.

Multifunctional Acetaminophen Interlayer for High Efficiency and Durability Lead-Lean Perovskite Solar Cells

Due to the easy oxidation of Sn2+, which leads to form tin vacancy defects and poor perovskite film quality, caused by the rapid crystallization rate in tin-based perovskite solar cells (PSCs), their efficiency lags far behind that of lead-based PSCs. To improve the photovoltaic (PV) performance and stability of FA0.9PEA0.1SnI3-based PSCs (T-PSCs), a small amount of Pb(SCN)2 is introduced into a perovskite precursor as an antioxidant, and acetaminophen (ACE) with various functional groups is used to modify a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/perovskite interface. The results show that the Pb(SCN)2 additive and ACE interfacial modification can not only optimize energy level alignment in T-PSCs but also inhibit Sn2+ oxidation to reduce the trap-state density, resulting in promoted carrier transport. The synergetic effect of the Pb(SCN)2 antioxidant and ACE interfacial modification significantly reduces nonradiative recombination and improves the PV performance and stability of T-PSCs. Consequently, the unsealed T-PSCs with the Pb(SCN)2 additive and ACE modification achieve a champion efficiency of 12.04% and maintain 99% of their initial PCE after being stored in N2 for more than 2100 h, while reference T-PSCs demonstrate a champion PCE of 6.20% and retain only 72% of its initial PCE. Moreover, the modified T-PSCs without encapsulation demonstrate much better stability in humid air.

Synergistic Buried Interface Regulation of Tin-Lead Perovskite Solar Cells via Co-Self-Assembled Monolayers

Tin-lead (Sn-Pb) perovskite solar cells (PSCs) hold considerable potential for achieving efficiencies near the Shockley-Queisser (S-Q) limit. Notably, the inverted structure stands as the preferred fabrication method for the most efficient Sn-Pb PSCs. In this regard, it is imperative to implement a strategic customization of the hole selective layer to facilitate carrier extraction and refine the quality of perovskite films, which requires effective hole selectivity and favorable interactions with Sn-Pb perovskites. Herein, we propose the development of Co-Self-Assembled Monolayers (Co-SAM) by integrating both [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) and glycine at the buried contacts. The one-step deposition process employed in the fabrication of the Co-SAM ensures uniform coverage, resulting in a homogeneous surface potential. This is attributed to the molecular interactions occurring between 2PACz and glycine in the processing solution. Furthermore, the amine (-NH2) and ammonium (-NH3+) groups in glycine effectively passivate Sn4+ defects at the buried interface of Sn-Pb perovskite films, even under thermal stress. Consequently, the synergistic buried interface regulation of Co-SAM leads to a power conversion efficiency (PCE) of 23.46%, which outperforms devices modified with 2PACz or glycine alone. The Co-SAM-modified Sn-Pb PSC demonstrates enhanced thermal stability, maintaining 88% of its initial PCE under 65 °C thermal stress for 590 h.

Strategies for Improving Efficiency and Stability of Inverted Perovskite Solar Cells

Perovskite solar cells (PSCs) have attracted widespread research and commercialization attention because of their high power conversion efficiency (PCE) and low fabrication cost. The long-term stability of PSCs should satisfy industrial requirements for photovoltaic devices. Inverted PSCs with a p-i-n architecture exhibit considerable advantages because of their excellent stability and competitive efficiency. The continuously broken-through PCE of inverted PSCs shows huge application potential. This review summarizes the developments and outlines the characteristics of inverted PSCs including charge transport layers (CTLs), perovskite compositions, and interfacial regulation strategies. The latest effective CTLs, interfacial modification, and stability promotion strategies especially under light, thermal, and bias conditions are emphatically analyzed. Furthermore, the applications of the inverted structure in high-efficiency and stable tandem, flexible photovoltaic devices, and modules and their main obstacles are systematically introduced. Finally, the remaining challenges faced by inverted devices are discussed, and several directions for advancing inverted PSCs are proposed according to their development status and industrialization requirements.

Synthesis of Hybrid Tin-Based Perovskite Microcrystals for LED Applications

Considerable focus on tin-based perovskites lies on substitution to leadhalide perovskites for the fabrication of eco-friendly optoelectronic devices. The major concern related to tin-based perovskite devices are mainly the stability and the efficiency. However, thinking on the final commercialization scope, other considerations such as precursor stability and cost are major factors to carry about. In this regard, this work presents a robust and facile synthesis of 2D A2SnX4 (A = 4-fluorophenethylammonium(4-FPEA); X = I, Br, I/Br) and 3D FASnI3 perovskite microcrystals following a developed synthesis strategy with low-cost starting materials. In this developed methodology, acetic acid is used as a solvent, which helps to protect from water by making a hydrophobic network over the perovskite surface, and hence provides sufficient ambient and long-term inert atmosphere stability of the microcrystals. Further, the microcrystals are recrystallized in thin films for LED application, allowing the fabrication of orange, near-infrared and purered emitting LEDs. The two-step recrystallized devices show better performance and stability in comparison to the reference devices made by using commercial precursors. Importantly, the developed synthesis methodology is defined as a generic method for the preparation of varieties of hybrid tin-based perovskites microcrystals and application in optoelectronic devices.

Adhesion-Controlled Heterogeneous Nucleation of Tin Halide Perovskites for Eco-Friendly Indoor Photovoltaics

The rapid development of the Internet of Things (IoT) has accelerated the advancement of indoor photovoltaics (IPVs) that directly power wireless IoT devices. The interest in lead-free perovskites for IPVs stems from their similar optoelectronic properties to high-performance lead halide perovskites, but without concerns about toxic lead leakage in indoor environments. However, currently prevalent lead-free perovskite IPVs, especially tin halide perovskites (THPs), still exhibit inferior performance, arising from their uncontrollable crystallization. Here, a novel adhesive bonding strategy is proposed for precisely regulating heterogeneous nucleation kinetics of THPs by introducing alkali metal fluorides. These ionic adhesives boost the work of adhesion at the buried interface between substrates and perovskite film, subsequently reducing the contact angle and energy barrier for heterogeneous nucleation, resulting in high-quality THP films. The resulting THP solar cells achieve an efficiency of 20.12% under indoor illumination at 1000 lux, exceeding all types of lead-free perovskite IPVs and successfully powering radio frequency identification-based sensors.

Day-Night imaging without Infrared Cutfilter removal based on metal-gradient perovskite single crystal photodetector

Day-Night imaging technology that obtains full-color and infrared images has great market demands for security monitoring and autonomous driving. The current mainstream solution relies on wide-spectrum silicon photodetectors combined with Infrared Cutfilter Removal, which increases complexity and failure rate. Here, we address these challenges by employing a perovskite photodetector based on Pb-Sn alloyed single crystal with a vertical bandgap-graded structure that presents variable-spectrum responses at different biases and extends the infrared detection range close to 1100 nm. Taking advantage of the Pb-Sn gradients in mobility and built-in field, the perovskite photodetector shows a large linear dynamic range of 177 dB. In addition, the optoelectronic characteristics feature long-term operational stability over a year. We further develop an imaging module prototype without Infrared Cutfilter Removal that exhibits excellent color fidelity with RGB color differences ranging from 0.48 to 2.46 under infrared interference and provides over 26-bit grayscale resolution in infrared imaging.

Triiodide Formation Governs Oxidation Mechanism of Tin-Lead Perovskite Solar Cells via A-Site Choice

Mixed tin-lead (Sn-Pb) halide perovskites stand out as promising materials for next-generation photovoltaics and near-infrared optoelectronics. However, their sensitivity to oxidative degradation remains a major hurdle toward their widespread deployment. A holistic understanding of their oxidation processes considering all their constituent ions is therefore essential to stabilize these materials. Herein, we reveal that A-site cation choice plays an inconspicuous yet crucial role in determining Sn-Pb perovskite stability toward oxidation. Comparing typical A-site compositions, we show that thin films and solar cells containing cesium are more resistant to oxidative stress relative to their methylammonium analogs. We identify degradation in these compositions to be closely linked to the presence of triiodide, a harmful species evolving from native I2 oxidants. We find that hydrogen bonding between methylammonium and I2 promotes triiodide formation, while the strong polarizing character of cesium limits this process by capturing I2. Inspired from these findings, we design two strategies to boost stability of sensitive methylammonium-based Sn-Pb perovskite films and devices against oxidation. Specifically, we modulate the polarizing character of surface A-sites in perovskite via CsI and RbI coatings, and we incorporate Na2S2O3 as an I2 scavenging additive. These crucial mechanistic insights will pave the way for the design of highly efficient and stable Sn-Pb perovskite optoelectronics.

Deciphering the Atomic-Scale Structural Origin for Photoluminescence Quenching in Tin-Lead Alloyed Perovskite Nanocrystals

The development of tin-lead alloyed halide perovskite nanocrystals (PNCs) is highly desirable for creating ultrastable, eco-friendly optoelectronic applications. However, the current incorporation of tin into the lead matrix results in severe photoluminescence (PL) quenching. To date, the precise atomic-scale structural origins of this quenching are still unknown, representing a significant barrier to fully realizing the potential of these materials. Here, we uncover the distinctive defect-related microstructures responsible for PL quenching using atomic-resolution scanning transmission electron microscopy and theoretical calculations. Our findings reveal an increase in point defects and Ruddlesden-Popper (RP) planar faults with increasing tin content. Notably, the point defects include a spectrum of vacancies and previously overlooked antisite defects with bromide vacancies and cation antisite defects emerging as the primary contributors to deep-level defects. Furthermore, the RP planar faults exhibit not only the typical rock-salt stacking pattern found in pure Pb-based PNCs but also previously undocumented microstructures rich in bromide vacancies and deep-level cation antisite defects. Direct strain imaging uncovers severe lattice distortion and significant inhomogeneous strain distributions caused by point defect aggregation, potentially breaking the local force balance and driving RP planar fault formation via lattice slippage. Our work illuminates the nature and evolution of defects in tin-lead alloyed halide perovskite nanocrystals and their profound impact on PL quenching, providing insights that support future material strategies in the development of less toxic tin-lead alloyed perovskite nanocrystals.

Manipulating the Crystallization of Tin Halide Perovskites for Efficient Moisture-to-Electricity Conversion

Manipulating the crystallization of perovskite in thin films is essential for the fabrication of any thin-film-based devices. Fabricating tin-based perovskite films from solution poses difficulties because tin tends to crystallize faster than the commonly used lead perovskite. To achieve optimal device performance in solar cells, the preferred method involves depositing tin perovskite under inert conditions using dimethyl sulfoxide (DMSO), which effectively retards the formation of the tin-bromine network, which is crucial for perovskite assembly. We found that under ambient conditions, a DMSO-based tin perovskite salt solution resulted in the formation of a two-phase system, SnBr4(DMSO)2 and MABr, whereas a dimethylformamide-based solution resulted in the formation of vacancy-ordered double perovskite MA2SnBr6. Humidity is known to solvate MABr to form the solvated ions, and so we used the two-phase system for the application in moisture to electricity conversion. The importance of the presence of the scaffold can be seen with the negligible power output from the vacancy-ordered double perovskite obtained with MA2SnBr6. We have fabricated a device with two-phase system that can generate an open-circuit potential of 520 mV and a short-circuit current density of 30.625 μA/cm2 at 85% RH. Also, the device charges a 10 μF capacitor from 150 mV at 51% RH to 500 mV at 85% RH in 6 s at a rate of 52.5 mV/s. Moreover, the output can be scaled by connecting devices in series and parallel configurations. A 527 nm green LED was powered by connecting five devices in series at 75% RH. This indicates a potential for utilizing these moisture-to-electricity conversion devices in powering low-energy requirement devices.

Chelating Dual Interface for Efficient and Stable Crystal Growth and Iodine Defect Management in Sn-Pb Perovskite Solar Cells

Suppressing Sn2+ oxidation and rationally controlling the crystallization process of tin-lead perovskite (Sn-Pb PVK) films by suitable bonding methods have emerged as key approaches to achieving efficient and stable Sn-Pb perovskite solar cells (PSCs). Herein, the chelating coordination is performed at the top and bottom interfaces of Sn-Pb PVK films. The chelation strength is stronger toward Sn2+ than Pb2+ by introducing oligomeric proanthocyanidins (OPC) at the bottom interface. This difference in chelation strength resulted in a spontaneous gradient distribution of Sn/Pb within the perovskite layer during crystallization, particularly enhancing the enrichment of Sn2+ at the bottom interface and facilitating the extraction and separation of photogenerated charge carriers in PSCs. Simultaneously, this top-down distribution of gradually increasing Sn content slowed down the crystallization rate of Sn-Pb PVK films, forming higher-quality films. On the top interface of the PVK, trifluoroacetamidine (TFA) was used to inhibit the generation of iodine vacancies (VI) through chelating with surface-uncoordinated Pb2+/Sn2+, further passivating defects while suppressing the oxidation of Sn2+. Ultimately, the PSCs with simultaneous chelation at both top and bottom interfaces achieved a power conversion efficiency (PCE) of 23.31% and an open-circuit voltage (VOC) exceeding 0.90 V. The stability of unencapsulated target devices in different environments also improved.

Monomolecular Membrane-Assisted Growth of Antimony Halide Perovskite/MoS2 Van der Waals Epitaxial Heterojunctions with Long-Lived Interlayer Exciton

Epitaxial growth stands as a key method for integrating semiconductors into heterostructures, offering a potent avenue to explore the electronic and optoelectronic characteristics of cutting-edge materials, such as transition metal dichalcogenide (TMD) and perovskites. Nevertheless, the layer-by-layer growth atop TMD materials confronts a substantial energy barrier, impeding the adsorption and nucleation of perovskite atoms on the 2D surface. Here, we epitaxially grown an inorganic lead-free perovskite on TMD and formed van der Waals (vdW) heterojunctions. Our work employs a monomolecular membrane-assisted growth strategy that reduces the contact angle and simultaneously diminishing the energy barrier for Cs3Sb2Br9 surface nucleation. By controlling the nucleation temperature, we achieved a reduction in the thickness of the Cs3Sb2Br9 epitaxial layer from 30 to approximately 4 nm. In the realm of inorganic lead-free perovskite and TMD heterojunctions, we observed long-lived interlayer exciton of 9.9 ns, approximately 36 times longer than the intralayer exciton lifetime, which benefited from the excellent interlayer coupling brought by direct epitaxial growth. Our research introduces a monomolecular membrane-assisted growth strategy that expands the diversity of materials attainable through vdW epitaxial growth, potentially contributing to future applications in optoelectronics involving heterojunctions.

Multifunctionally Reusing Waste Solder to Prepare Highly Efficient Sn-Pb Perovskite Solar Cells

The preparation of perovskite components (PbI2 and SnI2) using waste materials is of great significance for the commercialization of perovskite solar cells (PSCs). However, this goal is difficult to achieve due to the purity of the recovered products and the easy oxidation of Sn2+. Here, a simple one-step synthetic process to convert waste Sn-Pb solder into SnI2/PbI2 and then applied as-prepared SnI2/PbI2 to PSCs for high additional value is adopted. During fabrication, Sn-Pb waste solder is also employed to serve as a reducing agent to reduce the Sn4+ in Sn-Pb mixed narrow perovskite precursor and hence remove the deep trap states in perovskite. The target PSCs achieved an efficiency of 21.04%, which is better than the efficiency of the device with commercial SnI2/PbI2 (20.10%). Meanwhile, the target PSC maintained an initial efficiency of 80% even after 800 h under continuous illumination, which is significantly better than commercial devices. In addition, the method achieved a recovery rate of 90.12% for Sn-Pb waste solder, with a lab-grade purity (over 99.8%) for SnI2/PbI2, and the cost of perovskite active layer reduced to 39.81% through this recycling strategy through calculation.

Navigating challenges and solutions for metal-halide and carbon-based electrodes in perovskite solar cells (NCS-MCEPSC): An environmental approach

The urgent need to shift to renewable energy is highlighted by rising global energy use and environmental issues like global warming from fossil fuel dependency. Perovskite solar cells (PSCs) stand out as a promising option, providing high efficiency and potential for cost-effective production. This study delves into the environmental concerns and viable solutions linked with metal-halide PSCs (M-PSCs) and carbon-based electrode PCSs (C-PSCs). It showcases the swift progress in PSC technology, highlighting its potential to deliver efficient and economical renewable energy options. Yet, the environmental implications of these technologies, especially the utilization of toxic lead (Pb) in M-PSCs and the issues of stability and degradation in C-PSCs, represent considerable hurdles for their broad application and sustainability. The paper details the recent advances in PSCs, focusing on enhancements in device efficiency and stability through innovative material combinations and device designs. Nonetheless, the environmental hazards linked to the dispersal of toxic substances from compromised or deteriorating PSCs into the ecosystem raise significant concerns. In particular, the risk of Pb from M-PSCs contaminating soil and aquatic ecosystems is a pressing issue for human and environmental health, spurring investigations into alternative materials and methods to diminish these impacts. The authors examine several strategies, including the introduction of Pb-free perovskites, encapsulation methods to block the escape of hazardous substances, and the recycling of PSC elements. The study stresses the necessity of aligning technological innovations with considerations for the environment and health, calling for ongoing research into PSC technologies that are sustainable and safe. This review highlights the need for detailed assessments of PSC technologies, focusing on their renewable energy contributions, environmental impacts, and strategies to mitigate these effects. The authors call for a cohesive strategy to develop PSCs that are efficient, cost-effective, eco-friendly, and safe for widespread use.

iso-BAI Guided Surface Recrystallization for Over 14% Tin Halide Perovskite Solar Cells

Tin-based perovskite solar cells (PSCs) are promising environmentally friendly alternatives to their lead-based counterparts, yet they currently suffer from much lower device performance. Due to variations in the chemical properties of lead (II) and tin (II) ions, similar treatments may yield distinct effects resulting from differences in underlying mechanisms. In this work, a surface treatment on tin-based perovskite is conducted with a commonly employed ligand, iso-butylammonium iodide (iso-BAI). Unlike the passivation effects previously observed in lead-based perovskites, such treatment leads to the recrystallization of the surface, driven by the higher solubility of tin-based perovskite in common solvents. By carefully designing the solvent composition, the perovskite surface is effectively modified while preserving the integrity of the bulk. The treatment led to enhanced surface crystallinity, reduced surface strain and defects, and improved charge transport. Consequently, the best-performing power conversion efficiency of FASnI3 PSCs increases from 11.8% to 14.2%. This work not only distinguishes the mechanism of surface treatments in tin-based perovskites from that of lead-based counterparts, but also underscores the critical role in designing tailor-made strategies for fabricating efficient tin-based PSCs.

Tailoring Single-Mode Random Lasing of Tin Halide Perovskites Integrated in a Vertical Cavity

The development of random lasing (RL) with predictable and controlled properties is an important step to make these cheap optical sources stable and reliable. However, the design of tailored RL characteristics (emission energy, threshold, number of modes) is only obtained with complex photonic structures, while the simplest optical configurations able to tune the RL are still a challenge. This work demonstrates the tuning of the RL characteristics in spin-coated and inkjet-printed tin-based perovskites integrated into a vertical cavity with low quality factor. When the cavity mode is resonant with the photoluminescence (PL) peak energy, standard vertical lasing is observed. More importantly, single mode RL operation with the lowest threshold and a quality factor as high as 1 000 (twenty times the quality factor of the resonator) is obtained if the cavity mode lies above the PL peak energy due to higher gain. These results can have important technological implications toward the development of low-cost RL sources without chaotic behavior.

Defect Modulation via SnX2 Additives in FASnI3 Perovskite Solar Cells

Tin halide perovskites suffer from high defect densities compared with their lead counterparts. To decrease defect densities, SnF2 is commonly used as an additive in tin halide perovskites. Herein, we investigate how SnF2 compares to other SnX2 additives (X = F, Cl, Br) in terms of electronic and ionic defect properties in FASnI3. We find that FASnI3 films with SnF2 show the lowest Urbach energies (EU) of 19 meV and a decreased p-type character, as probed with ultraviolet photoemission spectroscopy. The activation energy of ion migration, as probed with thermal admittance spectroscopy, for FASnI3 with SnF2 is 1.33 eV, which is higher than with SnCl2 and SnBr2, which are 1.22 and 0.79 eV, respectively, resulting in less ion migration. Because of improved defect passivation, the champion power conversion efficiency of FASnI3 with SnF2 is 7.47% and only 1.84% and 1.20% with SnCl2 and SnBr2, respectively.