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We describe highly efficient and stable bifacial perovskite solar cells incorporating carbon nanotube network films as a back contact enabling perovskite/CIS 4-terminal tandem solar cells to reach apower conversion efficiency of over 27%.

Proper thermal management of solar cells based on metal halide perovskites (MHPs) is key to increasing their efficiency as well as their durability. Although two-dimensional (2D) MHPs possess enhanced thermal stability as compared to their three-dimensional (3D) counterparts, the lack of comprehensive knowledge of the heat transfer mechanisms dictating their ultralow thermal conductivities is a bottleneck for further improvements in their thermal performance. Here, we experimentally and computationally study the Dion-Jacobson (DJ) and Ruddlesden-Popper (RP) phases of MHPs (

We have evaluated the effectiveness of optical basicity, a chemical model, to predict and categorize the reaction behavior between calcia-magnesia-aluminosilicate (CMAS) deposits and ZrO2-based thermal barrier coatings (TBCs), which are used to insulate and protect metallic components in gas-turbine engines. The attack behavior of two CMAS compositions (Na-lean and Na-rich) with 7 wt% Y2O3-partially-stabilized ZrO2 (7YSZ) and 2ZrO2·Y2O3(ss) free-standing TBCs at 1340 °C were evaluated and compared to previous studies. The behavior of Y3+ in the reaction is correlated with the optical basicity of the CMAS; more basic Na-rich CMAS melt resulted in lower Y-solubility and higher Y-content in the reprecipitated ZrO2 grains than observed in the highly acidic CMAS attack for both tested TBCs. This behavior is consistent with previous studies of basic and acidic melts, and suggests that less acidic CMASs pose a unique danger to ZrO2-based TBCs that rely on Y-rich secondary phases for CMAS mitigation.

Summary Although great progress is being made toward improving the power conversion efficiency (PCE) and the operational stability of perovskite solar cells (PSCs), little attention is being paid to their mechanical reliability, which is particularly important for flexible PSCs (f-PCSs). Here, we have grown low-dimensional (LD) metal-halide perovskite (MHP) thin capping layer over the 3D MHP light-absorber thin film in f-PSCs in situ to improve their mechanical reliability. This resulted in f-PSCs with unprecedented, simultaneous improvements in PCE (21.0%), operational stability (T90, retention of 90% of the initial PCE, >800 h), and bending durability (T80 = 20,000 tension-only bending cycles). These synergistic virtuous effects are attributed to the LD MHP capping layer enhancing photocarriers extraction, providing protection against the environment, and “sealing” surface flaws on the 3D MHP thin film. The latter reduces the propensity for cracking in bending, which results in improved environmental stability and bending durability.

A combination of characterization techniques has been used to provide new understanding of the complex crystallization behavior of as-sprayed amorphous Yb2Si2O7-based air-plasma-sprayed environmental barrier coatings (EBCs). During crystallization heat-treatment, initially a mixture of metastable α-Yb2Si2O7 and X1-Yb2SiO5 phases form, along with stable β-Yb2Si2O7 and X2-Yb2SiO5 phases. Eventually the metastable phases transform to the stable β-Yb2Si2O7 (major) and X2-Yb2SiO5 (minor) phases. The significant volume expansion associated with these transformations partially contributes towards the anomalous expansion measured in these EBCs after crystallization, but it does not account for all the measured expansion. In this context, in similar EBCs, it is also observed that the porosity increases upon crystallization heat-treatment, primarily in the form of thin, interconnected pores, which also contributes to the measured anomalous expansion. Based on this understanding, guidelines are provided for ‘near-net-shape’ crystallization of phase-pure, dense β-Yb2Si2O7 EBCs that are free of vertical cracks.

Sn(II) halide perovskites are a less toxic alternative to Pb-based materials in perovskite solar cells, but oxidation to Sn(IV) introduces additional degradation pathways. Improving stability requi...

Tougher solar cell interfaces The low formation energies of the active layers in perovskite solar cells lead to low-toughness materials that are compliant and soft, which limits their interface stability and long-term reliability. Dai et al. show that treatment with iodine-terminated self-assembled monolayers that react with surface hydroxyl groups (which ultimately creates unwanted charge traps and voids) leads to a 50% increase of adhesion toughness between the electron transport layer and a mixed-composition perovskite thin film. The projected point at which 80% of the operating efficiency in perovskite solar cells was still retained increased from ∼700 to 4000 hours for 1-sun exposure with continuous maximum power point tracking. Science , this issue p. 618

Summary The development of mixed tin-lead (Sn-Pb)-based perovskite solar cells (PSCs) with low band gap (1.2–1.4 eV) has become critical not only for pushing single-junction devices toward the maximum efficiency given by the Shockley-Queisser limit, but also for enabling all-perovskite tandem devices beyond this limit. However, achieving high power-conversion efficiency (PCE) and long-term device operation stability simultaneously remains a significant challenge for Sn-Pb-based PSCs. Here, we demonstrate near ideal-band-gap (∼1.34 eV) methylammonium-free Sn-Pb-based PSCs with high efficiency (∼20%) and promising operational stability of maintaining >80% of initial PCE over 750 h under maximum-power-point tracking. The key to this success is the use of a SnCl2⋅3FACl complex additive that improves the microstructure and reduces the development of residual stress in the Sn-Pb perovskite thin films, which in turn enhances the efficiency and stability of the Sn-Pb-based ideal-band-gap PSCs.

Ion migration is a solid-state electrochemical phenomenon widely observed in the family of halide perovskite materials, which is attributed to their intrinsically soft ionic crystal structures and ...

The perovskite solar cell has emerged rapidly in the field of photovoltaics as it combines the merits of low cost, high efficiency, and excellent mechanical flexibility for versatile applications. However, there are significant concerns regarding its operational stability and mechanical robustness. Most of the previously reported approaches to address these concerns entail separate engineering of perovskite and charge-transporting layers. Herein we present a holistic design of perovskite and charge-transporting layers by synthesizing an interpenetrating perovskite/electron-transporting-layer interface. This interface is reaction-formed between a tin dioxide layer containing excess organic halide and a perovskite layer containing excess lead halide. Perovskite solar cells with such interfaces deliver efficiencies up to 22.2% and 20.1% for rigid and flexible versions, respectively. Long-term (1000 h) operational stability is demonstrated and the flexible devices show high endurance against mechanical-bending (2500 cycles) fatigue. Mechanistic insights into the relationship between the interpenetrating interface structure and performance enhancement are provided based on comprehensive, advanced, microscopic characterizations. This study highlights interface integrity as an important factor for designing efficient, operationally-stable, and mechanically-robust solar cells., Operational stability and mechanical robustness remain as engineering bottlenecks in perovskite solar cells technology. Here, Dong et al. introduce an interpenetrating perovskite at the electron-transporting-layer interface that enables a 1000-hour stable operation and high endurance against bending fatigue over 2500 cycles.

Metal halide perovskites (MHPs) are known to undergo several structural phase transitions, from lower to higher symmetry, upon heating. While structural phase transitions have been investigated by a wide range of optical, thermal and electrical methods, most measurements are quasi-static and hence do not provide direct information regarding the fundamental timescale of phase transitions in this emerging class of semiconductors. Here we investigate the timescale of the orthorhombic-to-tetragonal phase transition in the prototypical metal halide perovskite, methylammonium lead triiodide (CH3NH3PbI3 or MAPbI3) using cryogenic nanosecond transient absorption spectroscopy. By using mid-infrared pump pulses to impulsively heat up the material at slightly below the phase-transition temperature and probing the transient optical response as a function of delay time, we observed a clean signature of a transient, reversible orthorhombic-to-tetragonal phase transition. The forward phase transition is found to proceed at tens of nanoseconds timescale, after which a backward phase transition progresses at a timescale commensurate with heat dissipation from the film to the underlying substrate. A high degree of transient phase transition is observed accounting for one third of the steady-state phase transition. In comparison to fully inorganic phase-change materials such as VO2, the orders of magnitude slower phase transition in MAPbI3 can be attributed to the large energy barrier associated with the strong hydrogen bonding between the organic cation and the inorganic framework. Our approach paves the way for unraveling phase transition dynamics in MHPs and other hybrid semiconducting materials.

The curious phenomenon of cracking in organic-inorganic halide perovskite (OIHP) thin films for solar cells during scanning electron microscopy (SEM) can be seen in literally thousands of published SEM micrographs. Here we demonstrate, for the first time, the mechanisms responsible for this e-beam-induced damage in OIHP thin films, which is precluding their detailed SEM-characterization and understanding. The e-beam-induced rapid volatilization of the organic species from the OIHP surface in the SEM results in localized shrinkage and buildup of tensile stresses. These stresses drive grain-boundaries cracking, resulting in a ‘mud-cracking’ pattern that is influenced by the thin-film grain size.

Organic-inorganic halide perovskite (OIHP) thin films at the heart of the new perovskite solar cells (PSCs) are very brittle, limiting the mechanical reliability of PSCs. Here we show that fine-grained MAPbI3 (prototypical OIHP) films with grain size (~290 nm) smaller than the typical film thickness (~500 nm) tend to fracture intergranularly, resulting in low toughness (0.41 J.m−2). In contrast, MAPbI3/substrate interfacial fracture occurs in films with grains larger (~730 nm) than the film thickness, resulting in much higher toughness (1.14 J.m−2). Thus, coarse-grained OIHP films are deemed desirable for not only improved PSCs performance and stability but also mechanical reliability.

The sensitive detection of low-dose X-ray radiation is essential to many X-ray applications. In this article, the ultrasensitive X-ray detector based on pure Cs2AgBiBr6 all-inorganic lead-free perovskite film is successfully demonstrated and encapsulated using a metal casing with a Be window. The high-quality Cs2AgBiBr6 films are obtained through the low-cost solution process with long electron–hole diffusion length (~700 nm) and long carrier lifetime (~750 ns). Benefiting from the excellent properties of the Cs2AgBiBr6 film and the stable ambient provided by the packaging module, the resulting device exhibits attractive X-ray detection capabilities with a minimum detectable dose rate of 145.2 ${\mathrm {nGy}}_{air}\text{s}^{-1}$ and a detection sensitivity up to $1.8\times 10^{4}\,\,\mu {\mathrm {CGy}}_{air}{}^{-1}$ cm−2, which is about a thousand times higher than the sensitivity achieved with commercial a-Se X-ray detectors. Besides, the encapsulated device maintains superior detection performance after 2 months of storage, indicating the favorable reliability of the encapsulated device. This article demonstrates a possibility to use Cs2 AgBiBr6 perovskite film and Be window for the sensitive X-ray detection, which will inspire further development of radiation electronics by utilizing all-inorganic lead-free perovskite.

In nanocomposites, improved mechanical performance is critically linked to understanding and controlling interfacial properties. In the work reported here, ion implantation is introduced as a new method for tailoring the complex nanoscale interfaces between multiwall carbon nanotubes (MWCNTs) and a ceramic matrix. The results show that surface layers of the nanocomposite with high toughness can be created with C2+ ions. This enhanced toughening due to ion implantation is associated with large compressive stresses in the MWCNTs and with significant changes in the carbon structure. These observations are consistent with molecular dynamics (MD) simulations, which indicate that partial amorphization of the MWCNTs is enhanced by the compressive stress and confinement within the ceramic matrix. This work opens up new opportunities for using ion implantation to create a new class of exceptionally tough ceramic nanocomposites.

Despite huge improvements in power conversion efficiencies of perovskite solar cells, the technology is still limited by fill factors at around 80%. Here, we report perovskite solar cells having ex...

While grain boundaries (GBs) in conventional inorganic semiconductors are frequently considered as detrimental for photogenerated carrier transport, their exact role remains obscure for the emerging hybrid perovskite semiconductors. A primary challenge for GB-property investigations is that experimentally they need to be performed at the top surface, which is not only insensitive to depth-dependent inhomogeneities but also could be susceptible to topographic artifacts. Accordingly, we have developed a unique approach based on tomographic atomic force microscopy, achieving a fully-3D, photogenerated carrier transport map at the nanoscale in hybrid perovskites. This reveals GBs serving as highly interconnected conducting channels for carrier transport. We have further discovered the coexistence of two GB types in hybrid perovskites, one exhibiting enhanced carrier mobilities, while the other is insipid. Our approach reveals otherwise inaccessible buried features and previously unresolved conduction pathways, crucial for optimizing hybrid perovskites for various optoelectronic applications including solar cells and photodetectors., The role of grain boundaries (GBs) in halide perovskite is an interesting topic but existing investigations are limited to the top surface. Here Song et al. employ tomographic AFM to study the buried features of grains and GBs, revealing coexistence of interconnected conducting and inert GBs.

Summary Ceramic solid electrolytes are important emerging materials with the potential to enable the safe use of Li-metal anodes. However, they suffer from inherently low fracture toughness, which significantly limits battery performance and reliability. While small electrolyte dimensions are generally needed for faster ion transport, these length scales also restrict the approaches that can be used to engineer higher fracture resistance. Inspired by the toughening that reduced graphene oxide provides to polymers and engineering ceramics, this study explores the use of rGO to enhance the toughness of an oxide-based lithium-ion conductor. Materials with a greater than 2-fold enhancement in the average KIC are demonstrated. To our knowledge, this is the toughest ceramic solid electrolyte yet reported. Based on these results, an analytical framework is developed to provide guidelines for the design of ultra-tough solid electrolytes using 2D materials.

Pure formamidinium lead triiodide (α-FAPbI3) organic-inorganic halide perovskite (OIHP) semiconductor is very attractive for use as light absorber in the new thin-film perovskite solar cells (PSCs) technology. This is primarily because of its superior thermal stability, more suitable bandgap, and compositional simplicity. However, the existence of the photo-inactive non-perovskite δ-FAPbI3 polymorph (‘yellow’ phase) is a major hurdle in the path towards the development of α-FAPbI3-based PSCs. Also, there is general consensus that the fine-grained nature of OIHP thin films is detrimental to the environmental stability and performance of the resulting PSCs. In this context, here we take advantage of the polymorphism in FAPbI3, and use solvent-vapor-assisted δ-to-α phase transformation to induce exceptional grain coarsening (up to 50-fold) in 0.3-μm thickness FAPbI3 thin films, resulting in an unprecedented average grain size of up to ~9 μm. The underlying mechanisms are elucidated based on the results from a combination of some key experiments, which involve studying systematically the effects of time, temperature, initial grain size, and solvent polarity index (PI). The ultra-coarse-grained α-FAPbI3 thin films show dramatically improved environmental stability over their medium-grained counterparts, which is explained based on grain-boundary density arguments. PSCs made using the ultra-coarse-grained α-FAPbI3 thin films have improved photovoltaic (PV) performance, but it is somewhat modest. This is attributed to the underestimation of the effective grain size relevant to photocarrier dynamics.

Tin-based halide perovskite solar cells (PSCs) hold the most promise among lead-free PSCs, but they are plagued with inadequate environmental stability and power-conversion efficiency (PCE). Here w...

Organic–inorganic halide perovskites feature excellent optoelectronic properties but poor chemical stability. While passivating perovskite grain boundary (GB) by polymers shows prospects on long-te...

Analytical and empirical solutions to engineering problems are usually preferred because of their convenience in applications. However, they are not always accessible in complex problems. A new class of solutions, based on machine learning (ML) models such as regression trees and neural networks (NNs), are proposed and their feasibility and value are demonstrated through the analysis of fracture toughness measurements. It is found that both solutions based on regression trees and NNs can provide accurate results for the specific problem, but NN-based solutions outperform regression-tree-based solutions in terms of their simplicity. This example demonstrates that ML solutions are a major improvement over analytical and empirical solutions in terms of both reliable functionality and rapid deployment. When analytical solutions are not available, the use of ML solutions can overcome the limitations of empirical solutions and substantially change the way that engineering problems are solved.

Halide perovskite semiconductors exhibit ultralow thermal conductivities, making them potentially suitable for thermoelectric applications. Nevertheless, the thermoelectric properties of the protot...

Printable mesoscopic perovskite solar cells are usually fabricated by drop-casting perovskite precursor solution on a screen-printed mesoporous TiO2/ZrO2/carbon triple-layer followed by thermal annealing. They have attracted much attention due to their simple fabrication process and remarkable stability. However, challenges lie in how to achieve complete pore fillings of perovskites in the meso-pores and to obtain high-quality perovskite crystals. Here, we report an in situ crystal transfer (ICT) process based on gas-solid interaction to deposit perovskite CH3NH3PbI3 absorber in the scaffold. CH3NH3PbI3 single crystals are first transformed into a liquid phase via exposure to methylamine gas flow. After complete infiltration into the nano-structured scaffolds, the liquid phase is converted back to the solid phase with reduction of methylamine gas partial pressure, maintaining the high-quality of CH3NH3PbI3 single crystals. Compared with the conventional drop-casting method, the ICT method effectively leads to interconnected morphology and prolongs the charge-carrier lifetime (from ∼37.52 ns to ∼110.85 ns) of the perovskite absorber in the scaffold. As a result, the devices can deliver a power conversion efficiency of 15.89%, which is attributed to the suppressed charge recombination and correspondingly enhanced open-circuit voltage of 0.98 V.

Sulfide glasses are emerging as potential electrolytes for solid-state batteries. The mechanical behavior of these materials can significantly impact cell performance, and it is thus imperative to understand their deformation and fracture mechanisms. Previous work mainly reports properties obtained under quasi-static loading conditions, but very little is known about deformation under dynamic conditions. The current investigation shows that the sulfide glass mechanical behavior is dominated by viscoplasticity, differing substantially from polycrystalline oxide and sulfide solid electrolytes. Finite element modeling indicates that the sulfide glass stiffness is high enough to maintain good contact with softer lithium metal electrodes under moderate stack pressures. The observed viscoplasticity also implies that battery operating conditions will play an important role in electro-chemo-mechanical processes that are associated with dendritic lithium penetration. In general, the rate-dependent mechanical behavior of the sulfide glass electrolytes documented here offers a new dimension for designing next-generation all-solid-state batteries. Published version The authors acknowledge financial support from SK Innovation and the National Science Foundation (DMR-2124775).

Traces of heavy metals found in water resources, due to mining activities and e-waste discharge, pose a global threat. Conventional treatment processes fail to remove toxic heavy metals, such as lead, from drinking water in a resource-efficient manner when their initial concentrations are low. Here, we show that by using the yeast Saccharomyces cerevisiae we can effectively remove trace lead from water via a rapid mass transfer process, achieving an uptake of up to 12 mg lead per gram of biomass in solutions with initial lead concentrations below 1 part per million. We found that the yeast cell wall plays a crucial role in this process, with its mannoproteins and β-glucans being the key potential lead adsorbents. Furthermore, we discovered that biosorption is linked to a significant increase in cell wall stiffness. These findings open new opportunities for using environmentally friendly and abundant biomaterials for advanced water treatment targeting emerging contaminants.One-Sentence SummaryRemoving toxic heavy metals from water at challenging trace levels in an environmentally friendly, resource-efficient manner.

Two key interfaces in flexible perovskite solar cells (f-PSCs) are mechanically reinforced simultaneously: one between the electron-transport layer (ETL) and the 3D metal-halide perovskite (MHP) thin film using self-assembled monolayer (SAM), and the other between the 3D-MHP thin film and the hole-transport layer (HTL) using an in situ grown low-dimensional (LD) MHP capping layer. The interfacial mechanical properties are measured and modeled. This rational interface engineering results in the enhancement of not only the mechanical properties of both interfaces but also their optoelectronic properties holistically. As a result, the new class of dual-interface-reinforced f-PSCs has an unprecedented combination of the following three important performance parameters: high power-conversion efficiency (PCE) of 21.03% (with reduced hysteresis), improved operational stability of 1000 h T

A high-speed, wide-field photoluminescence (PL) imaging method is established for measuring carrier diffusion in formamidinium lead triiodide (FAPbI3) perovskite thin films. This method allows tran...

The stability of formamidinium lead iodide (FAPbI3) perovskites is generally improved by incorporating cesium (Cs) into the crystal structure. However, the effectiveness of this approach is limited...

Methylammonium lead iodide (MAPbI3) has attracted great interest as an organic–inorganic hybrid perovskite for photovoltaic applications. Vacancy-mediated ion migration is one of the dominant carrier transport mechanisms in MAPbI3. Our previous work clarified the nature of migrating species and their moderating effect on electronic transport. However, to develop strategies to mitigate ion migration and its impact thereof, it is important to know whether the migration is homogeneous or controlled by microstructural features, such as grain boundaries. In this work, we implement temperature-dependent pulsed voltage–current measurements of MAPbI3 thin films with different grain sizes under dark conditions and distinguish the electromigration of iodine vacancies and methylammonium vacancies. Upon increasing the grain size, the total accumulated charge decreases, whereas the activation energies increase. This is consistent with the high grain boundary density in small-grained films responsible for facilitating ...

The “dark” current–voltage (I–V) response of CH3NH3PbI3 organic–inorganic halide perovskite (OIHP) thin films is studied as a function of temperature, voltage, and scan rate to investigate the nature of the I–V hysteresis. This is to address the apparent discrepancy observed in characteristics of the I–V hysteresis. Depending on the measurement conditions, two complementary mechanisms appear to control the I–V behavior. First, ionic species contribute to the conduction, and because of their slow-moving nature, a slower scan rate gives ions enough time to take part in conduction (i.e., below a relaxation frequency). Second, migration of ionic species to the interface(s) modulates the Schottky junction and, consequently, the electronic transport across the interfaces. Therefore, a slower scan rate results in more charge accumulation at the interface, which leads to a decrease in the leakage current. These findings provide an explanation that resolves the ongoing debate regarding the characteristics of the I...

There has been an urgent need to eliminate toxic lead from the prevailing halide perovskite solar cells (PSCs), but the current lead-free PSCs are still plagued with the critical issues of low efficiency and poor stability. This is primarily due to their inadequate photovoltaic properties and chemical stability. Herein we demonstrate the use of the lead-free, all-inorganic cesium tin-germanium triiodide (CsSn0.5Ge0.5I3) solid-solution perovskite as the light absorber in PSCs, delivering promising efficiency of up to 7.11%. More importantly, these PSCs show very high stability, with less than 10% decay in efficiency after 500 h of continuous operation in N2 atmosphere under one-sun illumination. The key to this striking performance of these PSCs is the formation of a full-coverage, stable native-oxide layer, which fully encapsulates and passivates the perovskite surfaces. The native-oxide passivation approach reported here represents an alternate avenue for boosting the efficiency and stability of lead-free PSCs., Replacing the toxic lead in the state-of-the-art halide perovskite solar cells is highly desired but the device performance and stability are usually compromised. Here Chen et al. develop inorganic cesium tin and germanium mixed-cation perovskites that show high operational stability and efficiency over 7%.

Developing an efficient single component photocatalyst for overall water splitting under visible-light irradiation is extremely challenging. Herein, we report a metal-free graphitic carbon nitride (g-CxN4)-based nanosheet photocatalyst (x = 3.2, 3.6, or 3.8) with melem rings conjugated by Schiff-base bonds (N[double bond, length as m-dash]C-C[double bond, length as m-dash]N). The presence of the conjugated Schiff-base bond tunes the band gap of g-CxN4 and, more importantly, serves as an electron sink to suppress electron-hole pair recombination. The projected density of states (PDOS) calculations suggest that the melem ring and Schiff-base bond act as oxidizing and reducing centers, respectively, for photocatalytic water splitting. As a result, g-CxN4, in particular g-C3.6N4, can catalyze overall water splitting without the need for any co-catalyst or sacrificial donor. Under visible light (>420 nm wavelength) irradiation, g-C3.6N4 catalyzes the overall water splitting with H2 and O2 generation rates of 75.0 and 36.3 μmol h-1 g-1, respectively. g-C3.6N4 is the most efficient single-component photocatalyst ever reported for overall water splitting. Our studies demonstrate a new approach for tuning the bandgap and the electronic structure of graphitic carbon nitride for maximizing its photocatalytic performance for water splitting, which will be important for hydrogen generation and for energy applications.

Grain boundary is the key interface in polycrystalline halide perovskite semiconductors and devices. In this work, first, we present a fundamental discussion on the role of grain boundaries in determining the carrier-transport properties and the (electro)chemical stability of halide perovskites. Then, we demonstrate rational chemical approaches for tailoring grain boundaries in halide perovskite thin films, which will not only lead to the reduction of electronic/ionic defects, but also endow grain-boundaries with new functions. High-performance halide perovskite photovoltaic devices are achieved based on engineered grain boundary interfaces. Furthermore, we provide perspectives on the future research directions on halide perovskite grain boundaries for photovoltaics and beyond.

State-of-the-art halide perovskite solar cells have bandgaps larger than 1.45 eV, which restricts their potential for realizing the Shockley-Queisser limit. Previous search for low-bandgap (1.2 to 1.4 eV) halide perovskites has resulted in several candidates, but all are hybrid organic-inorganic compositions, raising potential concern regarding device stability. Here we show the promise of an inorganic low-bandgap (1.38 eV) CsPb0.6Sn0.4I3 perovskite stabilized via interface functionalization. Device efficiency up to 13.37% is demonstrated. The device shows high operational stability under one-sun-intensity illumination, with T80 and T70 lifetimes of 653 h and 1045 h, respectively (T80 and T70 represent efficiency decays to 80% and 70% of the initial value, respectively), and long-term shelf stability under nitrogen atmosphere. Controlled exposure of the device to ambient atmosphere during a long-term (1000 h) test does not degrade the efficiency. These findings point to a promising direction for achieving low-bandgap perovskite solar cells with high stability., Current research focus on the perovskites solar cells (PSCs) is mainly limited to the lead-based ones with bandgaps above 1.5 eV. Here Hu et al. report efficient and stable inorganic tin-containing PSCs, opening doors to exploring abundant perovskite materials with bandgaps lower than 1.4 eV.