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Through energy efficiency and demand flexibility, buildings can play a prominent role in mitigating the urgent and severe consequences associated with a changing climate. In this issue of Joule, the paper by Langevin et al. provides clear insight into the magnitude of impact buildings can have.

Expanded deployment of renewable energy technologies can help society mitigate climate change. However, solar and wind energy resources are inherently variable. In this issue of Joule, Hunter and colleagues quantitatively compare a diverse set of energy storage and backup power technologies that can help variable energy resources meet demand. They estimate current technology costs, consider improvement potential, and approximate the uncertainties.

As an abundant and ubiquitous energy source, solar energy has successfully demonstrated its potential in tackling the water-energy dilemma in an eco-friendly way. In this issue of Joule, Wenbin and co-authors creatively propose the co-generation of electricity and freshwater via an integrated PV-membrane distillation system.

Jyotirmoy Mandal completed his PhD in Applied Physics at Columbia University in the City of New York and is currently a Schmidt Science Fellow and a postdoctoral researcher at University of California, Los Angeles. His research interests include low-cost optical designs for radiative cooling and solar heating, with a focus on applications in developing countries. Yuan Yang is an associate professor in the Department of Applied Physics and Applied Mathematics at Columbia University in the City of New York. His research interests include electrochemical energy storage and thermal energy management. Dr. Yang has published over 70 peer-reviewed journal articles, including in leading journals such as Science, Proceedings of the National Academy of Sciences, Advanced Materials, and Joule. Nanfang Yu is an associate professor in the Department of Applied Physics and Applied Mathematics at Columbia University in the City of New York. His research interests include mid-infrared and far-infrared optics, metamaterials, biophotonics, and biologically inspired flat optics. Dr. Yu’s research has been published in leading journals like Science, Nature Materials, Nature Nanotechnology, and Joule. Aaswath P. Raman is an assistant professor of Materials Science and Engineering at the University of California, Los Angeles (UCLA). He is also co-founder and chief scientific officer of SkyCool Systems, a startup commercializing radiative cooling technologies. Dr. Raman’s research interests include nanophotonics, metamaterials, radiative heat transfer, and energy applications, including radiative cooling. His works have been published in leading journals such as Nature, Nature Energy, Physical Review Letters, and Joule.

Microbial electrosynthesis is increasingly popular, as it couples renewable electricity to microbial metabolism. Currently, electromicrobial production (EMP) to synthesize fuels has yet to surpass laboratory-scale reactions, but continuing improvements in the cost efficiency of these technologies hold promise for their translation to the real world. In this issue of Joule, Barstow and coworkers introduce a computational framework to determine the maximum efficiency of EMP, providing a blueprint for the scaling and broad implementation of these unique, renewable energy systems.

In this issue of Joule, the study by Lu et al. on spontaneous solar syngas production from CO2 driven by energetically favorable wastewater microbial anodes demonstrated a microbial photoelectrochemical system that combines oxidation of organic wastes in wastewater with photocathodic CO2 reduction reaction. Spontaneous CO2 reduction using the energy stored from sunlight and microorganisms incites the (bio)electrochemical system to the next stage by making CO2 reduction independent from additional energy sources.

The search for enhanced energy density is fueling global research in battery science and engineering, where applications spanning consumer electronics, electric vehicles, and grid-scale energy storage are stimulating enormous industrial growth. While higher-energy-density batteries will combat range anxiety hampering EV adoption, it is not the only metric of importance; across a breadth of applications from implanted devices to space exploration, there are various requirements for safer, cheaper, and more durable batteries, as well as those that can be sourced from widely available materials and readily recycled. In this issue of Joule, Zhou and co-workers outline a 500 Wh/kg battery based on anionic redox between Li2O and Li2O2, demonstrated at the pouch cell level, providing a new benchmark for gravimetric energy density.

In this issue of Joule, Dahn and coworkers present the development of a hybrid lithium-ion/lithium-metal cell that allows for an extra boost of capacity when needed. This battery has the potential to help eliminate range anxiety with electric vehicles.

Hydrogen peroxide is the focus of growing attention for distributed manufacturing, reflecting its decentralized applications and shipping hazards. Two recent reports, one in Science by Wang and colleaugues and one in this issue of Joule by Surendranath, Hatton, and colleaugues, introduce innovative electrochemical methods to produce electrolyte-free aqueous solutions of hydrogen peroxide.

In this issue of Joule, Ilse et al. have presented a comprehensive look at soiling losses seen in photovoltaic systems around the world and quantified the threshold allowable cost for some commonly proposed mitigation measures. Their analysis shows significant differences in economic feasibility of mitigation measures in regional markets based on their soiling rates.

Micro-supercapacitors are attracting increasing attention due to their potential applications in multiple real-world energy scenarios such as wearable electronic devices, powering the internet of things, and medical applications. While tremendous efforts are being made in the performance enhancement, one of the bottleneck issues inhibiting their upscaling is the complicated manufacturing process. In this issue of Joule, Bruce Dunn and colleagues demonstrated a fully processable micro-supercapacitor engaging a photopatternable hydroxide ion conducting solid electrolyte, which is thermally and dimensionally stable with a high conductivity of 10 mS cm−1.The micro-supercapacitor composites of VN and NiCo2O4 electrodes and the [AMIM][OH]/SU-8 hydroxide-conducting solid electrolyte show high areal capacitance of 250 mF cm−2 at 20 mV s−1 sweep rate, which is one of the highest performances among reported results.

One of the key arguments for carbon pricing is that it will induce additional innovation in green technologies, yet most models used to evaluate carbon pricing policies either completely ignore induced technological change or are dependent on ad hoc assumptions. In this issue of Joule, Wang et al. estimate the historical relationship between improvements in energy efficiency and energy’s share of costs. Incorporating this relationship into a standard integrated assessment model effectively reduces the carbon price required to meet emissions reduction thresholds.

Raising the price of carbon can reduce greenhouse gas emissions and galvanize a clean economy transition. Meeting the Paris Agreement not only requires reducing emissions to zero this century but further demands the mass removal of carbon dioxide from the atmosphere. Recently in Joule Daggash and Mac Dowell report that higher carbon pricing alone will not incentivize atmospheric CO2 removal and instead propose a complementary credit for negative emissions.

Translating homogeneous electrocatalysts to surface-immobilized electrocatalysts, while maintaining catalytic activity, has long been a research challenge. In this issue of Joule, Le Goff and coworkers report a surface-confined dinuclear copper electrocatalyst for O2 reduction that mimics the active site of multi-copper oxidases.

Although solid electrolyte interphase (SEI) formation is an important factor in battery performance, difficulties in characterizing the SEI mean that it is still not well understood. In this issue of Joule, Nanda and coworkers utilize tip-enhanced Raman spectroscopy to paint a more complete picture of the SEI on silicon electrodes.

Lithium sulfur batteries are endowed with intriguingly high energy density but also suffer from complicated interfacial parasitic reactions, especially toward the anode side. In this issue of Joule, Zhang et al. design a new LiN(SO2CF2H)(SO2CF3)(LiDFTFSI)/poly(ethylene oxide) solid-state polymer electrolyte that is compatible with polysulfide chains and can regulate the interfacial chemistry of lithium anode.

Interface concern is one of the most critical issues to fully utilize the exceptional energy storage capability enabled by solid-state electrolyte and Li metal anode. In this issue of Joule, Whitacre, Matyjaszewski, and co-workers presented a semiliquid lithium metal anode (SLMA) flowable at room temperature to afford sufficient contacts with solid-state electrolyte, outlining a practical strategy to achieve a conformal interface for favorable ion conduction.

In this issue of Joule, the fabrication and characterization of colored, visually opaque, but IR-transparent textiles are reported by the research groups of Yi Cui and Shanhui Fan. Coloration is achieved by imbedding inorganic pigment nanoparticles into IR-transparent polyethylene fibers.

Sgouridis et al. present an interesting analysis, focusing on the energy requirements for carbon capture and storage and scalable renewable energy technologies. It focuses on one key metric, the energy returned on energy invested: how much useful energy (to society) you get out per joule of energy you put in.

Electrical power generation, air conditioning, electronics thermal management—these applications all rely on condensation. This issue of Joule features two articles on condensation: Boreyko and co-workers describe the effect of surface orientation on condensation on a superhydrophobic surface, and Varanasi and colleagues demonstrate a coating method that enhances condensation of organic fluids. These findings represent a significant step toward system-level efficiency improvements in energy-intensive applications.

Efficient engineering design of CO2 and CO electrolysis systems is key to achieving practical renewable energy conversion and storage via the upgrading of CO2. High selectivity, current density, and energy efficiency have been the focus of many research efforts. The single-pass conversion of the reactants is another crucial system parameter that has—until now—received too little attention. Recently in Joule, Ripatti et al. showcase an electrolyzer that achieves high single-pass conversion combined with high current density.

Translating model studies of oxygen reduction electrocatalysts for real devices is significant for the practical applications of fuel cells. In recent papers published in Joule and Science, both Sun’s group and Liu’s group report Pt-Co catalysts for fuel cells, exceeding the DOE 2020 performance targets, making fuel cells approach reality.

The discovery and development of blue light emitting diodes (LEDs) enabled energy-efficient white light emission that continues to impact global energy consumption today. Alternative materials that can outcompete commercial blue LEDs based on epitaxial InGaN could have a large impact on the lighting industry and in curbing anthropogenic climate change. Recently in Joule, Congreve and colleagues show that metal halide perovskite nanocrystals—greatly improved by Mn incorporation—have promise for low-cost, efficient, and bright blue LEDs.

Lithium metal is known to form ramified structures during electrodeposition not only at high current densities (above diffusion limit) but also, unexpectedly, at low currents. In this issue of Joule, Bai and coworkers describe an analytical approach to explain structural evolution of lithium electrode at different current densities. They find three distinct regimes as a function of current rate, such that the morphology changes from whiskers to mossy to dendrites.

The rate at which emerging photovoltaic modules are fabricated is an important lever to reduce manufacturing costs, one often underrepresented in solar cell research. In this issue of Joule, Rolston and co-authors demonstrate rapid, air-ambient spray deposition of metal halide perovskite thin films at a rate of 12 m/min for efficient solar cell modules. Their findings point to the feasibility of scaling up perovskite photovoltaics at competitive costs, provided key issues with material instability can be solved.

Metal-organic frameworks (MOFs) and their composites and derivatives, with high porosity and tailorable chemical components, have recently aroused tremendous research interest in renewable energy and environmental science. In this inaugural issue of Joule , Lou and coworkers 1 summarize the latest progresses in the fabrication strategies of MOF-based materials and their applications in gas adsorption, energy conversion, and storage, while Dincâ and colleagues 2 demonstrate the promising application of MOFs in thermoelectrics.

The rapid rise in efficiencies of lead halide perovskite solar cells has hastened the case for commercialization. One of the key barriers, however, is stability of devices. In this issue of Joule, Zhou et al. studied the degradation mechanism of a FA-Cs mixed cation perovskite-based solar cell with experimental and modeling techniques to show that phase separation into FA-rich and Cs-rich compositions account for the observed degradation.

In this issue of Joule, Steffen et al. tackle a challenging topic to quantify and project costs for operation and maintenance (O&M) of solar and wind power plants in Germany. They note that O&M costs can be 20%–25% of overall costs and find that such costs have decreased, resulting in common overestimates of O&M costs.

An effective design of stretchable Li metal anode is of paramount importance but remains a big challenge for high-energy-density stretchable lithium battery. In this issue of Joule, for the first time, Yi Cui and colleagues demonstrate an ingenious mechanically stretchable Li metal anode, achieving good stretchability and stable electrochemical performance with a high Coulombic efficiency (97.5%) over 176 cycles. This perfect design provides an inspiration for the future development of high-energy-density stretchable lithium battery.

The development of new functional materials has been historically driven by the interplay of intelligent human innovation, manual trial and error, and a dash of luck. In this issue of Joule, Correa-Baena and colleagues offer a visionary perspective on the future of computational-aided accelerated materials discovery for clean tech and beyond.

Stability of small area perovskite solar cells has been notably improved, but large area modules have not been proven stable. Recently in Joule, E. Bi and coworkers present a highly stable perovskite module that kept 90% of its initial efficiency after 1,000 h operation under illumination. The secret is an iodide diffusion blocking layer (DBL) added at the module interconnection. The DBL with 2D graphitic carbon nitride (g-C3N4) flakes can suppress iodide diffusion at the interconnection and prevent electrode corrosion.

Internet connected devices are limited by the performance of microbatteries that power them. In this issue of Joule, Hur et al. develop microbatteries with tall 3D electrodes that have high areal energy densities. These microbatteries were fabricated on a silicon wafer using silicon and polymer processing that are compatible with microelectronics, paving the way for future microbattery and microelectronics integration.

Solar cell development has focused heavily on improving the efficiency under a standard reference spectrum representative of temperate climates. These conditions are rarely met in the field. In this issue of Joule, Peters and Buonassisi use open-source atmospheric satellite data to predict the electricity produced from a solar cell of given bandgap installed at any location globally.

In this issue of Joule, Guoxiu Wang, Yury Gogotsi, and collaborators design and synthesize highly porous MXene electrodes that are resistant to nanosheet restacking and deliver high electroadsorption capacity for capacitive deionization (CDI) of saline water. In CDI cells constructed with aerogel-like Ti3C2Tx MXene electrodes, an adsorption capacity of 118 mg/cm3 (45 mg/g) was achieved in a 10,000 mg/L salt solution, more than one order of magnitude greater than carbon-based electrode materials.

The high promise of lithium metal batteries is grounded by concerns of safety and instability. In this issue of Joule , Zhang and colleagues show that coating carbon fiber networks with silver greatly enhances the infiltration of molten lithium and forms a robust metal alloy interface. This enables stable cycling at high current densities of full cell batteries with both LiFePO 4 and sulfur-based cathodes.

Understanding the factors that influence energy consumption is important for better-informed energy forecasting. In this issue of Joule , Sekar, Williams, and Chen have developed a model to correlate U.S. energy consumption with how individuals are spending their time. It was found that Americans are staying at home on average 8 more days in 2012 than they were in 2003, leading to a net 1,700 trillion BTU in energy savings, 1.8% of the national total for that year.

In this issue of Joule , Ohno et al. have come closer to developing a detailed microscopic structure-property link between a given thermodynamic state and its corresponding carrier information. By taking a promising Zintl thermoelectric compound, Mg 3 Sb 2 , as a prototype, the authors developed a guideline for identifying multiple "hidden" thermoelectric materials with different thermodynamic states within a nominally identical composition.

Electrochemical reduction of CO 2 to formate is a promising approach to utilize intermittent renewable energy for high-value chemical storage and to mitigate carbon pollution. Demanding applied targets for this process require that the reaction is sustained at a high current density with near-unity product efficiency. In this issue of Joule , Zheng and De Luna et al. show that incorporating sulfur into tin catalysts greatly increases the reaction rate while maintaining high selectivity and robust stability.

In this issue of Joule , Guihua Yu and colleagues broaden the design space for redox flow batteries by pushing forward the concept of using an alternative class of electrolytes based on deep eutectic solvents. Through judicious materials selection and cell design, they assemble a hybrid redox flow battery platform that achieves high energy density with low-cost and environmentally benign components. They additionally perform a fundamental characterization study of the chemical speciation and complexation phenomena in the electrolyte to guide further optimization and overcome remaining performance challenges.

The authors are founding team members of a new effort to develop an Open Energy Outlook for the United States. The effort aims to apply best practices of policy-focused energy system modeling, ensure transparency, build a networked community, and work toward a common purpose: examining possible US energy system futures to inform energy and climate policy efforts. Individual author biographies can be found on the project website: https://openenergyoutlook.org/. DeCarolis et al. articulate the benefits of forming collaborative teams with a wide array of disciplinary and domain expertise to conduct analysis with macro-energy system models. Open-source models, tools, and datasets underpin such efforts by enabling transparency, accessibility, and replicability among team members and with the broader modeling community.

High temperature epitaxial growth has been a long-standing requirement for forming semiconductor thin films with exceptional optoelectronic properties. In this issue of Joule , Brenes and coworkers have demonstrated that atmospheric and photoinduced post-treatments of solution-processed polycrystalline metal halide perovskites can improve the diffusion length, carrier lifetime, and surface recombination velocity to values previously only achievable by single crystal materials.

In the inaugural issue of Joule , Chunsheng Wang, Kang Xu, and colleagues demonstrate a groundbreaking advance in Li-ion battery electrolytes with their design and demonstration of 4 V aqueous Li-ion batteries, which in theory could eliminate several environmental, safety, and manufacturing restrictions and concerns raised by non-aqueous electrolytes.

Recently in Joule, Gilbert and Bazilian argue that nuclear microreactors could be developed to provide a commercially viable source of distributed electricity generation. While microreactors are technically feasible to construct, the options for providing the same energy services using lower-cost renewables and storage brings into question the necessity of developing a nuclear option.

In this issue of Joule, Palmstrom and coworkers present efficient solution-processed two-terminal solar cells employing two metal halide perovskite-based absorbers. The key to this achievement is 2-fold: the deposition of a thin yet robust transparent conductor in between the two sub-cells allows solution processing of the back-cell and enables efficient and local charge recombination. Furthermore, the insertion of large cations reduces halide segregation and enables a higher open-circuit voltage and stability for the high-band-gap sub-cell.

Thermoelectric materials development is a complex balancing act between electronic and thermal transport properties, which often have opposing optimization strategies. Researchers are always seeking new options for tailoring thermoelectric materials. In this issue of Joule, Pei, Ge, and colleagues unveil a new two-pronged attack for reducing thermal conductivity without perturbing electrical conductivity. This approach, yielding high zT values exceeding 2.5 at 900 K, should inspire similar approaches in other common thermoelectric materials.

The absence of low-platinum, high-activity, and satisfied-durability electrocatalysts for oxygen reduction reaction has bottlenecked the wide adoption of proton exchange membrane fuel cells for decades. In this issue of Joule, Sun and coworkers introduce a class of atomic-ordering L10 CoPt electrocatalyst for oxygen reduction catalysis, which exceeds the DOE 2020 technique target in both liquid half-cell and membrane electrode assembly conditions, representing a promising strategy to overcome this long-standing barrier.

This issue of Joule features an article by Wang et al. that demonstrates that high-efficiency tin-based solar cells can be realized by the formation of a heterostructure consisting of two-dimensional (2D) and three-dimensional (3D) perovskites based on phenylethylammonium tin iodide (PEA2SnI4) and formamidinium tin iodide (FASnI3), respectively, forming from the study of the PEA2(FA)n-1SnnI3n+1 system. The authors convincingly show that these self-assembled heterostructures can be manipulated and ordered sequentially by chemical means, thus providing a new avenue for further improving the perovskite solar cell technology.

Effective renewable energy policy decisions need to be backed with robust data and analysis. With new solar cell directives, it is important to know the location and capacity of existing installations. In this issue of Joule, Yu and colleagues report on the design, development, and application of DeepSolar—a comprehensive deep learning generated database of solar cell installations in the contiguous US.

Before 2017, almost all understanding of battery behavior was based on non-alive techniques where the intrinsic structure and chemistry of the material of interest may get lost in the sample preparation process. The morphology of the solid electrolyte interphase (SEI) layer is essential to reveal a battery’s condition and operating principles. To reduce irradiation damage from high-energy electron beams, cryoelectron microscopy techniques are adapted for battery research. In this issue of Joule, Yi Cui and colleagues characterized the SEI morphology to elucidate its relationship to battery behavior.

Semitransparent photovoltaics installed onto windows can generate power and regulate temperature in buildings and vehicles. In this issue of Joule, Lunt et al. show the potential for wide-bandgap metal halide perovskite materials in visibly transparent solar cells and Yip et al. demonstrate a new design to block infrared radiation in tinted polymer photovoltaics.