Halide homogenization for low energy loss in 2-eV-bandgap perovskites and increased efficiency in all-perovskite triple-junction solar cells

Science

Inverted (pin) perovskite solar cells (PSCs) afford improved operating stability in comparison to their nip counterparts but have lagged in power conversion efficiency (PCE). The energetic losses responsible for this PCE deficit in pin PSCs occur primarily at the interfaces between the perovskite and the charge-transport layers. Additive and surface treatments that use passivating ligands usually bind to a single active binding site: This dense packing of electrically resistive passivants perpendicular to the surface may limit the fill factor in pin PSCs. We identified ligands that bind two neighboring lead(II) ion (Pb2+) defect sites in a planar ligand orientation on the perovskite. We fabricated pin PSCs and report a certified quasi–steady state PCE of 26.15 and 24.74% for 0.05– and 1.04–square centimeter illuminated areas, respectively. The devices retain 95% of their initial PCE after 1200 hours of continuous 1 sun …

Laser-written Nitrogen Vacancy (NV−) centers are combined with transfer-printed GaN micro-lenses to increase fluorescent light collection by reducing total internal reflection at the planar diamond interface. We find a 2x improvement of fluorescent light collection using a 0.95 NA air objective at room temperature, in agreement with FDTD simulations. The nature of the transfer print micro-lenses leads to better performance with lower Numerical Aperture (NA) collection, as confirmed by results with a 0.5NA air objective which show improvement greater than 5x. The approach is attractive for scalable integrated quantum technologies.

Advanced Functional Materials

All‐inorganic perovskite cesium lead triiodide (CsPbI3) with inorganic nature, low‐temperature synthesis, and a suitable bandgap is desirable for high‐performance photovoltaics. However, the scalable production of CsPbI3 photovoltaics is still challenging due to a large nucleation energy barrier and slow phase transition during unassisted natural crystallization. Here, the crystallization dynamics of CsPbI3 thin films is tailored via lead acetate (PbAc2) substitution in the perovskite precursor ink, allowing the scalable fabrication of efficient all‐inorganic perovskite solar cells and minimodules. Introducing PbAc2 enlarges CsPbI3 colloid size in the precursor and reduces the nucleation energy barrier. Additionally, reactions between acetate and dimethylammonium in the wet film accelerate the removal of dimethylammonium additives and generate solvent vapors for self‐regulate internal solvent annealing, resulting in …

Metal halide perovskite semiconductors are excellent materials for next-generation solar cells. As a result of research and development all over the world, the photoelectric conversion efficiency for single-cell devices has rapidly improved to over 26% (as of July 2023), while the record efficiency for silicon-on-perovskite tandem devices currently stands at 33.7% (reported in May 2023). Materials chemistry has made many important contributions toward these remarkable results. In this account, we will introduce our achievements in these areas of material chemistry research for improving the performance of perovskite photovoltaics, including the development of high-purity precursor materials, and precursor inks tailored for large-area printed perovskite films. Studies of the nucleation and crystallization process, including simulations, have led to the reliable fabrication of high-quality perovskite films. Diverse new …

Matter

In electrochemical CO2 reduction (CO2R) into chemicals and fuels, it is a long-standing challenge to suppress the competing hydrogen evolution reaction (HER) and steer selectivity to a single valuable product. Ethylene is a desired model molecule in light of its large market size, range of applications from polymers to sustainable aviation fuel, and large present-day carbon intensity. The reaction pathways and reactivity of CO2R rely on catalyst surface properties and local reaction environments. Here we review the mechanistic understanding of CO2R to ethylene; we then discuss catalyst design strategies in light of the link between catalyst structure, reaction pathways, and ethylene production performance. We close with challenges in catalyst design and provide an outlook for further research directions to accelerate the rational design of catalysts.

ACS Energy Letters

Perovskite solar cells (PSCs) in the pin structure are limited by nonradiative recombination at the electron transport layer (ETL) interface, which is exacerbated in narrow-bandgap (∼1.2 eV) Pb–Sn PSCs due to surface Sn oxidation and detrimental p-doping. Photoluminescence quantum yield studies herein indicated that ethane-1,2-diammonium (EDA) passivation only partially alleviates perovskite/ETL energetic losses. We pursued passivation of the defect-rich perovskite:ETL interface to reduce nonradiative losses; our target was to combine chemical coordination of Sn sites with the introduction of an interlayer, which we implemented by introducing long-chain carboxylic acid ligands at the perovskite surface. Treatment with oleic acid (OA) led to reduced recombination at the perovskite/ETL interface and evidence of Sn2+ coordination. This reduced the VOC deficit of Pb–Sn PSCs to 0.34 V, resulting in a 0.89 V V …

Advanced Materials

Hydrogenation of biomass‐derived chemicals is of interest for the production of biofuels and valorized chemicals. Thermochemical processes for biomass reduction typically employ hydrogen as the reductant at elevated temperatures and pressures. Here we investigate direct electrified reduction of 5‐Hydroxymethylfurfural (HMF) to a precursor to bio‐polymers, 2,5‐bis(hydroxymethyl)furan (BHMF). Noting a limited current density in prior reports of this transformation, we investigated the use of a hybrid catalyst consisting of ternary metal nanodendrites mixed with a cationic ionomer, the latter purposed to increase local pH and facilitate surface proton diffusion. We found that the approach, when implemented using Ga‐doped Ag‐Cu electrocatalysts designed for p‐d orbital hybridization, steered selectivity to BHMF, achieving a faradaic efficiency of 58% at 100 mA/cm2 and a production rate of 1 mmol/cm2/h, this latter …

Chemistry–A European Journal

Polar crystalline materials, a subset of the non‐centrosymmetric materials, are highly sought after. Their symmetry properties make them pyroelectric and also piezoelectric and capable of second‐harmonic generation (SHG). For SHG and piezoelectric applications, metal oxides are commonly used. The advantages of oxides are durability and hardness – downsides are the need for high‐temperature synthesis/processing and often the need to include toxic metals. Organic polar crystals, on the other hand, can avoid toxic metals and can be amenable to solution‐state processing. While the vast majority of polar organic molecules crystallize in non‐polar space groups, we found that both 7‐chloro‐1,3,5‐triazaadamantane, for short Cl‐TAA, and also the related Br‐TAA (but not I‐TAA) form polar crystals in the space group R3m, easily obtained from dichloromethane solution. Measurements confirm piezoelectric and …

Advanced Functional Materials

Two dimensional/three‐dimensional (2D/3D) metal halide perovskite heterostructures have attracted great interest in photovoltaic and light‐emitting diode (LEDs) applications. In both, their implementation results in an improvement in device efficiency yet the understanding of these heterostructures remains incomplete. In this work the role of organic cations, essential for the formation of 2D perovskite structures is unraveled, in a range of metal halide perovskite heterostructures. These heterostructures are used to fabricate efficient green perovskite LEDs and a strong dependence between cation content and device performance is shown. The crystal structure, charge‐carrier transport and dynamics, and the electronic structure of these heterostructures are studied and it is shown that the presence of crystalline 2D perovskite inhibits electron injection and ultimately lowers device performance. This work highlights the …

CO2 electrolyzers have progressed rapidly in energy efficiency and catalyst selectivity toward valuable chemical feedstocks and fuels, such as syngas, ethylene, ethanol, and methane. However, each component within these complex systems influences the overall performance, and the further advances needed to realize commercialization will require an approach that considers the whole process, with the electrochemical cell at the center. Beyond the cell boundaries, the electrolyzer must integrate with upstream CO2 feeds and downstream separation processes in a way that minimizes overall product energy intensity and presents viable use cases. Here we begin by describing upstream CO2 sources, their energy intensities, and impurities. We then focus on the cell, the most common CO2 electrolyzer system architectures, and each component within these systems. We evaluate the energy savings and the …

The project is intended to research the influence of microstructure of grain boundaries on the radiative recombination activities of Cu (In, Ga) S2 solar cells. Two microscopy techniques were used, cathodoluminescence (CL) and electron backscatter diffraction (EBSD). The CL data was acquired by an Attolight Allalin 4027 Chronos dedicated CL-SEM with a 150 l/mm and 700 nm blazed grating. All CL maps were acquired with 3 kV beam energy, 1.25 nA measurement current, and 50 µm aperture size. The CL data was processed by the python library Lumispy. An indepth tutorial in how to use Lumispy can be found here: https://docs. lumispy. org/en/latest/EBSD data was measured by a Zeiss GeminiSEM equipped with Oxford Instruments HKL Symmetry S3 detector. The software used in data acquisition is AZtec 4.0. The stepsize of maps is 30 µm and the phase for indexing is cubic zinc blende phase. The data was processed and analysed by MTEX, and open-sourced Matlab toolbox. All measurements were done at room temperature.

Advanced Materials

All‐perovskite tandem solar cells show great potential to enable the highest performance at reasonable costs for a viable market entry in the near future. In particular, wide‐bandgap (WBG) perovskites with higher open‐circuit voltage (VOC) are essential to further improve the tandem solar cells’ performance. Here, a new 1.8 eV bandgap triple‐halide perovskite composition in conjunction with a piperazinium iodide (PI) surface treatment is developed. With structural analysis, it is found that the PI modifies the surface through a reduction of excess lead iodide in the perovskite and additionally penetrates the bulk. Constant light‐induced magneto‐transport measurements are applied to separately resolve charge carrier properties of electrons and holes. These measurements reveal a reduced deep trap state density, and improved steady‐state carrier lifetime (factor 2.6) and diffusion lengths (factor 1.6). As a result, WBG …

All-perovskite tandem solar cells are attracting considerable interest in photovoltaics research, owing to their potential to surpass the theoretical efficiency limit of single-junction cells, in a cost-effective sustainable manner. Thanks to the bandgap-bowing effect, mixed tin−lead (Sn−Pb) perovskites possess a close to ideal narrow bandgap for constructing tandem cells, matched with wide-bandgap neat lead-based counterparts. The performance of all-perovskite tandems, however, has yet to reach its efficiency potential. One of the main obstacles that need to be overcome is the─oftentimes─low quality of the mixed Sn−Pb perovskite films, largely caused by the facile oxidation of Sn(II) to Sn(IV), as well as the difficult-to-control film crystallization dynamics. Additional detrimental imperfections are introduced in the perovskite thin film, particularly at its vulnerable surfaces, including the top and bottom interfaces as well …

Biomass incorporates carbon captured from the atmosphere and can serve as a renewable feedstock for producing valuable chemicals and fuels. Here we look at how electrochemical approaches can impact biomass valorization, focusing on identifying chemical transformations that leverage renewable electricity and feedstocks to produce valorized products via electro-privileged transformations. First, we recommend that the field should explore widening the spectrum of platform chemicals derived from bio-feedstocks, thus offering pathways to molecules that have historically been derived from petroleum. Second, we identify opportunities in electrocatalytic production of energy-dense fuels from biomass that utilize water as the hydrogen source and renewable electricity as the driving force. Finally, we look at the potential in electrochemical depolymerization to preserve key functional groups in raw feedstocks that …

This supplementary material contains fits of Frenkel-Poole emission and trap-assisted tunnelling to the current-voltage characteristics of Ti/Al/Ti/Au contacts to AlGaN/GaN heterostructures, annealed at 700 C for 30 s. The raw data for these fits will be provided in a later upload, alongside all other raw data for the paper this supports. Also given are transmission electron microscopy images of the AlGaN barrier in AlGaN/GaN heterostructures following annealing at different temperatures.

Chemical Communications

An open-cage bis[60]fulleroid (OC) was applied as an electron transport material (ETM) in tin (Sn) halide perovskite solar cells (PSCs). Due to the reduced offset between the energy levels of Sn-based perovskites and ETMs, the power conversion efficiency (PCE) of Sn-based PSCs with OC reached 9.6% with an open-circuit voltage (VOC) of 0.72 V. Additionally, OC exhibited superior thermal stability and provided 75% of the material without decomposition after vacuum deposition. The PSC using vacuum-deposited OC as the ETM could afford a PCE of 7.6%, which is a big leap forward compared with previous results using vacuum-deposited fullerene derivatives as ETMs.

Chemistry–A European Journal

Polar crystalline materials, a subset of the non‐centrosymmetric materials, are highly sought after. Their symmetry properties make them pyroelectric and also piezoelectric and capable of second‐harmonic generation (SHG). For SHG and piezoelectric applications, metal oxides are commonly used. The advantages of oxides are durability and hardness – downsides are the need for high‐temperature synthesis/processing and often the need to include toxic metals. Organic polar crystals, on the other hand, can avoid toxic metals and can be amenable to solution‐state processing. While the vast majority of polar organic molecules crystallize in non‐polar space groups, we found that both 7‐chloro‐1,3,5‐triazaadamantane, for short Cl‐TAA, and also the related Br‐TAA (but not I‐TAA) form polar crystals in the space group R3m, easily obtained from dichloromethane solution. Measurements confirm piezoelectric and …

Joule

Perovskite/perovskite/silicon triple-junction solar cells hold promise for surpassing their two-junction counterparts in performance. Achieving this requires monolithic integration of a ∼2.0 eV band-gap perovskite subcell, characterized by a high bromide:iodide ratio (>7:3), and with low-temperature processability and high optoelectronic quality. However, light-induced phase segregation in such perovskites remains a challenge. To address this, we propose modifying the wide-band-gap perovskite with potassium thiocyanate (KSCN) and methylammonium iodide (MAI) co-additives, where SCN− increases the perovskite grain size, reducing the grain boundary defect density; K+ immobilizes the halide, preventing the formation of halide vacancies; and MA+ eliminates the residual light-destabilizing SCN− in the perovskite films via double displacement reactions. Our co-additive strategy enables enhanced photostability …

Matter

Compressive strain engineering improves perovskite stability. Two-dimensional compressive strain along the in-plane direction can be applied to perovskites through the substrate; however, this in-plane strain results in an offsetting tensile strain perpendicular to the substrate, linked to the positive Poisson ratio of perovskites. Substrate-induced strain engineering has not yet resulted in state-of-the-art operational stability. Here, we seek instead to implement hydrostatic strain in perovskites by embedding lattice-mismatched perovskite quantum dots (QDs) into a perovskite matrix. QD-in-matrix perovskites show a homogeneously strained lattice as evidenced by grazing-incidence X-ray diffraction. We fabricate mixed-halide wide-band-gap (Eg; 1.77 eV) QD-in-matrix perovskite solar cells that maintain >90% of their initial power conversion efficiency (PCE) after 200 h of one-sun operation at the maximum power point …

Nature Communications

Electrosynthesis of acetate from CO offers the prospect of a low-carbon-intensity route to this valuable chemical––but only once sufficient selectivity, reaction rate and stability are realized. It is a high priority to achieve the protonation of the relevant intermediates in a controlled fashion, and to achieve this while suppressing the competing hydrogen evolution reaction (HER) and while steering multicarbon (C2+) products to a single valuable product––an example of which is acetate. Here we report interface engineering to achieve solid/liquid/gas triple-phase interface regulation, and we find that it leads to site-selective protonation of intermediates and the preferential stabilization of the ketene intermediates: this, we find, leads to improved selectivity and energy efficiency toward acetate. Once we further tune the catalyst composition and also optimize for interfacial water management, we achieve a cadmium-copper …

Nature Energy

As renewable energy generation increases, the impacts of weather and climate on energy generation and demand become critical to the reliability of the energy system. However, these impacts are often overlooked. Global climate models (GCMs) can be used to understand possible changes to our climate, but their coarse resolution makes them difficult to use in energy system modelling. Here we present open-source generative machine learning methods that produce meteorological data at a nominal spatial resolution of 4 km at an hourly frequency based on inputs from 100 km daily-average GCM data. These methods run 40 times faster than traditional downscaling methods and produce data that have high-resolution spatial and temporal attributes similar to historical datasets. We demonstrate that these methods can be used to downscale projected changes in wind, solar and temperature variables across …

Nature Energy

Chalcopyrite-based solar cells have reached an efficiency of 23.35%, yet further improvements have been challenging. Here we present a 23.64% certified efficiency for a (Ag,Cu)(In,Ga)Se2 solar cell, achieved through the implementation of a series of strategies. We introduce a relatively high amount of silver ([Ag]/([Ag] + [Cu]) = 0.19) into the absorber and implement a ‘hockey stick’-like gallium profile with a high concentration of Ga close to the molybdenum back contact and a lower, constant concentration in the region closer to the CdS buffer layer. This kind of elemental profile minimizes lateral and in-depth bandgap fluctuations, reducing losses in open-circuit voltage. In addition, the resulting bandgap energy is close to the local optimum of 1.15 eV. We apply a RbF post-deposition treatment that leads to the formation of a Rb–In–Se phase, probably RbInSe2, passivating the absorber surface. Finally, we …

Nature Energy

Surface reconstruction, chemo-mechanical degradation, and interfacial side reactions are major factors limiting the cyclability of Ni-rich cathodes. A strategy based on entropy-assisted epitaxial coating is now shown to effectively mitigate these issues, leading to improved battery performance and promising advances in electrochemical energy storage.

Nature Energy

In the online version of the article initially published, a PDF from a different article was included. This has now been corrected, and the PDF of this article is available to view online.

Nature Energy

The manufacturing of perovskite solar cells under ambient conditions is desirable, yet the efficiency of p–i–n perovskite solar cells fabricated in air still lags behind those made in an inert atmosphere. Here we introduce an ionic pair stabilizer, dimethylammonium formate (DMAFo), into the perovskite precursor solution to prevent the degradation of perovskite precursors. DMAFo inhibits the oxidization of iodide ions and deprotonation of organic cations, improving the crystallinity and reducing defects in the resulting perovskite films. We show the generation of additional p-type defects during ambient air fabrication that suggests the need for improving bulk properties of the perovskite film beyond surface passivation. Upon addition of DMAFo, we demonstrate that the efficiency of inverted p–i–n solar cells based on perovskite layers with 1.53-eV and 1.65-eV bandgaps fabricated under ambient conditions (25–30 °C, 35 …

Nature Energy

Lithium (Li) metal battery technology, renowned for its high energy density, faces practical challenges, particularly concerning large volume change and cell swelling. Despite the profound impact of external pressure on cell performance, there is a notable gap in research regarding the interplay between external pressure and the electroplating behaviours of Li+ in large-format pouch cells. Here we delve into the impact of externally applied pressure on electroplating and stripping of Li in 350 Wh kg−1 pouch cells. Employing a hybrid design, we monitor and quantify self-generated pressures, correlating them with observed charge–discharge processes. A two-stage cycling process is proposed, revealing controlled pouch cell swelling of less than 10%, comparable to state-of-the-art Li-ion batteries. The pressure distribution across the cell surface unveils a complex Li+ detour behaviour during electroplating …

Nature Energy

Although progress has been made in producing multi-carbon products from the electrochemical reduction of CO2, the modest selectivity for ethylene (C2H4) leads to low energy efficiency and high downstream separation costs. Here we functionalize Cu catalysts with a variety of substituted aryl diazonium salts to improve selectivity towards multi-carbon products. Using computation and operando spectroscopy, we find that Cu surface oxidation state (δ+ where 0 < δ < 1) can be tuned by functionalization and that it influences the selectivity to C2H4. We report a Faradaic efficiency and a specific current density for C2H4 as large as 83 ± 2% and 212 mA cm−2, respectively, on partially oxidized Cu0.26+. Using a CO gas feed, we demonstrate an energy efficiency of ~40% with a C2H4 Faradaic efficiency of 86 ± 2%, corresponding to a low electrical power consumption of 25.6 kWh Nm−3 for the CO to C2H4 …

Nature Energy

Ion (de)solvation at solid–electrolyte interfaces is pivotal for energy and chemical conversion technology, such as (electro)catalysis, batteries and bipolar membranes. For example, during the electrocatalytic hydrogen evolution reaction in alkaline media, water needs to be dissociated and hydroxide ions solvated—a process that is not well understood. Here we study water dissociation and ion solvation kinetics in isolation at polymeric bipolar membrane and electrolyte–metal interfaces. We discover bias-dependent relationships between the activation entropy and enthalpy, which we link to a bias-dependent dispersion of interfacial capacitance. Furthermore, our results indicate that OH− solvation is kinetically slower than H+ solvation and that the solvation kinetics display characteristics that are independent of the catalyst structure. We attribute this to a universal amount of excess charge needed to induce electric …

Nature Energy

The presence of mobile ions in metal halide perovskites has been shown to adversely affect the intrinsic stability of perovskite solar cells (PSCs). However, the actual contribution of mobile ions to the total degradation loss compared with other factors such as trap-assisted recombination remains poorly understood. Here we reveal that mobile ion-induced internal field screening is the dominant factor in the degradation of PSCs under operational conditions. The increased field screening leads to a decrease in the steady-state efficiency, often owing to a large reduction in the current density. Instead, the efficiency at high scan speeds (>1,000 V s−1), where the ions are immobilized, is much less affected. We also show that the bulk and interface quality do not degrade upon ageing, yet the open-circuit voltage decreases owing to an increase in the mobile ion density. This work reveals the importance of ionic losses for …

Nature Energy

Achieving extremely fast charging yet maintaining high energy density remains a challenge in the battery field. Traditional current collectors, being impermeable to electrolytes, hinder the movement of Li+ ions and restrict the high-rate capability of thick electrodes. Here we conceptualize a porous current collector for energy-dense and extremely fast-charging batteries. This porous design allows Li+ ions to pass through both the current collector and the separator simultaneously, thereby reducing the effective Li+ transport distance by half and quadrupling the diffusion-limited C-rate capability without compromising the energy density. Multilayer pouch cells equipped with this current collector demonstrate high specific energy (276 Wh kg−1) and remarkable fast-charging capabilities at rates of 4 C (78.3% state of charge), 6 C (70.5% state of charge) and 10 C (54.3% state of charge). This porous current collector …

Nature Energy

Hydrocarbon fuels can be synthesized from CO and water via Kölbel–Engelhardt synthesis, a thermocatalytic process in which temperatures of ≥200 °C and elevated pressures are typically needed. While light-driven hydrocarbon production by CO hydrogenation has been demonstrated under milder conditions, for this reaction H2 must first be sourced. Here we report the direct production of hydrocarbons from CO and water at atmospheric pressure via light-driven Kölbel–Engelhardt synthesis without external heating or the addition of H2. Using a TiO2-supported Ni catalyst, we obtain an activity of 8.83 mol−CH2− molNi−1 h−1 and C2+ selectivity higher than 55%. In situ spectroscopy and density functional theory calculations suggest that the migration of photogenerated electrons from TiO2 to Ni facilitates carbon–carbon coupling at the interface of the TiO2−x/Ni catalyst, which accounts for the observed high …

Nature Energy

The stabilization of grain boundaries and surfaces of the perovskite layer is critical to extend the durability of perovskite solar cells. Here we introduced a sulfonium-based molecule, dimethylphenethylsulfonium iodide (DMPESI), for the post-deposition treatment of formamidinium lead iodide perovskite films. The treated films show improved stability upon light soaking and remains in the black α phase after two years ageing under ambient condition without encapsulation. The DMPESI-treated perovskite solar cells show less than 1% performance loss after more than 4,500 h at maximum power point tracking, yielding a theoretical T80 of over nine years under continuous 1-sun illumination. The solar cells also display less than 5% power conversion efficiency drops under various ageing conditions, including 100 thermal cycles between 25 °C and 85 °C and an 1,050-h damp heat test.

Nature Energy

Polymers are key dielectric media for energy storage capacitors in power electronics for electric vehicles and solar panels, and there is an urgent need to enhance their discharged energy density (Ud) at high temperatures. Existing polymer–inorganic nanocomposites with high Ud cannot be produced by conventional roll-to-roll fabrication processes and exhibit compromised cyclic stability. In this study, we introduced phosphotungstic acid subnanosheets, a ‘reservoir’ for charges, into polymers to form a subnanocomposite. Even a low loading (0.2 wt%) of ultralarge, ultrathin, flexible subnanosheets was found to effectively strengthen polymers and hinder the propagation of breakdown paths. These subnanosheets can also trap charges through grafted surfactant molecules and polyoxometalate cluster backbones. An ultrahigh Ud of 7.2 J cm−3 with a charge–discharge efficiency of 90% and charge–discharge …

Nature Energy

The presence of mobile ions in metal halide perovskites has been shown to adversely affect the intrinsic stability of perovskite solar cells (PSCs). However, the actual contribution of mobile ions to the total degradation loss compared with other factors such as trap-assisted recombination remains poorly understood. Here we reveal that mobile ion-induced internal field screening is the dominant factor in the degradation of PSCs under operational conditions. The increased field screening leads to a decrease in the steady-state efficiency, often owing to a large reduction in the current density. Instead, the efficiency at high scan speeds (>1,000 V s−1), where the ions are immobilized, is much less affected. We also show that the bulk and interface quality do not degrade upon ageing, yet the open-circuit voltage decreases owing to an increase in the mobile ion density. This work reveals the importance of ionic losses for …

Nature Energy

The presence of mobile ions in metal halide perovskites has been shown to adversely affect the intrinsic stability of perovskite solar cells (PSCs). However, the actual contribution of mobile ions to the total degradation loss compared with other factors such as trap-assisted recombination remains poorly understood. Here we reveal that mobile ion-induced internal field screening is the dominant factor in the degradation of PSCs under operational conditions. The increased field screening leads to a decrease in the steady-state efficiency, often owing to a large reduction in the current density. Instead, the efficiency at high scan speeds (>1,000 V s−1), where the ions are immobilized, is much less affected. We also show that the bulk and interface quality do not degrade upon ageing, yet the open-circuit voltage decreases owing to an increase in the mobile ion density. This work reveals the importance of ionic losses for …

Nature Energy

Mixed halide wide-bandgap perovskites are suitable for integration in tandem photovoltaics such as perovskite/organic tandem solar cells. However, halide phase segregation originating from halogen vacancy-assisted ion migration in wide-bandgap perovskites limits the device efficiency and lifetime. Here we incorporate pseudo-halogen thiocyanate (SCN) ions in iodide/bromide mixed halide perovskites and show that they enhance crystallization and reduce grain boundaries. Trace amount of SCN ions in the bulk enter the perovskite lattice, forming an I/Br/SCN alloy, and occupy iodine vacancies, blocking halide ion migration via steric hindrance. Taken together, these effects retard halide phase segregation under operation and reduce energy loss in the wide-bandgap perovskite cells. The resulting perovskite/organic tandem solar cell achieves a power conversion efficiency of 25.82% (certified 25.06%) and an …

Nature Energy

While small-scale nuclear power is typically thought of for niche markets, recent work has suggested that it could help address the massive gaps in energy access in developing countries. However, nuclear energy has safety, governance and economic considerations that affect its deployment. Here we present a global analysis of regions suitable for nuclear reactor deployment based on physical siting criteria, security, governance and economic competitiveness. We use high-resolution population and satellite night-time light data to identify areas in need of electricity. We show that, technically, reactors in the 1–50 MWe range could serve 70.9% of this population. However, economics alone would make microreactors uncompetitive compared with renewables and energy storage for 87% of this population. Grid extensions and small modular nuclear reactors (with more competitive economics) could electrify these …

Nature Energy

The presence of mobile ions in metal halide perovskites has been shown to adversely affect the intrinsic stability of perovskite solar cells (PSCs). However, the actual contribution of mobile ions to the total degradation loss compared with other factors such as trap-assisted recombination remains poorly understood. Here we reveal that mobile ion-induced internal field screening is the dominant factor in the degradation of PSCs under operational conditions. The increased field screening leads to a decrease in the steady-state efficiency, often owing to a large reduction in the current density. Instead, the efficiency at high scan speeds (>1,000 V s−1), where the ions are immobilized, is much less affected. We also show that the bulk and interface quality do not degrade upon ageing, yet the open-circuit voltage decreases owing to an increase in the mobile ion density. This work reveals the importance of ionic losses for …

Nature Energy

Perovskite solar cells have seen impressive progress in performance and stability, yet maintaining efficiency while scaling area remains a challenge. Here we find that additives commonly used to passivate large-area perovskite films often co-precipitate during perovskite crystallization and aggregate at interfaces, contributing to defects and to spatial inhomogeneity. We develop design criteria for additives to prevent their evaporative precipitation and enable uniform passivation of defects. We explored liquid crystals with melting point below the perovskite processing temperature, functionalization for defect passivation and hydrophobicity to improve device stability. We find that thermotropic liquid crystals such as 3,4,5-trifluoro-4′-(trans-4-propylcyclohexyl)biphenyl enable large-area perovskite films that are uniform, low in defects and stable against environmental stress factors. We demonstrate modules with a …

Nature Energy

Although progress has been made in producing multi-carbon products from the electrochemical reduction of CO2, the modest selectivity for ethylene (C2H4) leads to low energy efficiency and high downstream separation costs. Here we functionalize Cu catalysts with a variety of substituted aryl diazonium salts to improve selectivity towards multi-carbon products. Using computation and operando spectroscopy, we find that Cu surface oxidation state (δ+ where 0 < δ < 1) can be tuned by functionalization and that it influences the selectivity to C2H4. We report a Faradaic efficiency and a specific current density for C2H4 as large as 83 ± 2% and 212 mA cm−2, respectively, on partially oxidized Cu0.26+. Using a CO gas feed, we demonstrate an energy efficiency of ~40% with a C2H4 Faradaic efficiency of 86 ± 2%, corresponding to a low electrical power consumption of 25.6 kWh Nm−3 for the CO to C2H4 …