Brief Reviews of Science: Volume 378, Issue 6626 (December 23, 2022)

This review is written by non-expert and used for personal study only.

Compositional texture engineering for highly stable wide-bandgap perovskite solar cells

• Solar Cells

Introduction

Tandem solar cells, which consist of two or more layers of photovoltaic materials, have the potential to achieve higher efficiency than single-layer cells. However, they often face challenges with open-circuit voltage and stable operation. This is especially true for cells that use mixed-halide perovskites, as they are prone to phase segregation under operating conditions.

Reducing Defects and Phase Segregation

To enhance the operational stability of wide-bandgap perovskite solar cells (PSCs), it is important to reduce the density of defective sites, which can help suppress bromine-iodine (Br-I) phase segregation. One strategy involves using the gas-quench method, which has been shown to improve the optoelectronic properties and operational stability of these cells.

Improved Performance with Gas-Quenching

The gas-quench process, when applied to Br-rich perovskite precursors, results in perovskite films with better optoelectronic properties and stability. This leads to higher power conversion efficiency (PCE) and open-circuit voltage in wide-bandgap PSCs.

Structural Advantages of the Gas-Quench Method

When comparing the structural properties of perovskite films prepared using the antisolvent and gas-quench methods, the latter shows a more dense and uniform morphology. This results in a smoother surface with less grain boundary defects, which contributes to the improved performance of the solar cells.

Optoelectronic Benefits of Gas-Quenching

The gas-quench method also has a positive impact on the optoelectronic properties of high-Br-content perovskite films. These films exhibit higher carrier mobility and longer diffusion lengths, which can be attributed to the suppression of halide phase separation and a reduction in defect density.

Monolithic All-Perovskite Tandem Solar Cells

By integrating narrow-bandgap and wide-bandgap perovskites, researchers have fabricated a monolithic all-perovskite tandem solar cell with a record PCE of $27.1\%$ and an open-circuit voltage of $2.2$ V. These tandem cells exhibit impressive long-term stability under various conditions.

Conclusion

The gas-quench method enhances the structural and optoelectronic properties of high-Br-content perovskite films, leading to efficient and stable all-perovskite tandem solar cells. By suppressing Br-I phase segregation and minimizing defects, this method can significantly improve the performance of wide-bandgap perovskite photovoltaics.

Required Additional Study Materials

• Y. Zhao, K. Zhu, Organic-inorganic hybrid lead halide perovskites for optoelectronic and electronic applications. Chem. Soc. Rev. 45, 655–689 (2016).
• G. E. Eperon, M. T. Hörantner, H. J. Snaith, Metal halide perovskite tandem and multiple-junction photovoltaics. Nat. Rev. Chem. 1, 0095 (2017).
• Y. Tong, A. Najar, L. Wang, L. Liu, M. Du, J. Yang, J. Li, K. Wang, S. F. Liu, Wide-bandgap organic-inorganic lead halide perovskite solar cells. Adv. Sci. 9, e2105085 (2022).
• H. S. Jung, N.-G. Park, Perovskite solar cells: From materials to devices. Small 11, 10–25 (2015).
• J. Wang, H. Liu, Y. Zhao, X. Zhang, Perovskite-based tandem solar cells gallop ahead. Joule 6, 509–511 (2022).
• R. Wang, T. Huang, J. Xue, J. Tong, K. Zhu, Y. Yang, Prospects for metal halide perovskite-based tandem solar cells. Nat. Photonics 15, 411–425 (2021).

Introductory material

• “Perovskite Photovoltaics: Basic to Advanced Concepts and Implementation” by Aparna Thankappan and Sabu Thomas

Reference

SCIENCE 22 Dec 2022 Vol 378, Issue 6626 pp. 1295-1300 DOI: 10.1126/science.adf019

Nanoscale covariance magnetometry with diamond quantum sensors

• Quantum Sensing

Introduction to Correlated Phenomena

In condensed matter physics, understanding how various physical properties are connected or correlated is crucial. These correlations can be observed in a wide range of settings, including quantum devices and fluctuating electromagnetic fields. Nitrogen vacancy (NV) centers in diamond are a promising tool for studying these correlations, as they are stable and capable of detecting tiny changes at the nanoscale level. By using pairs of NV centers to measure spatiotemporal correlations, we can gain insights into how systems evolve over time and space.

Detection of Local Magnetic Fields

When two NV centers are exposed to a shared magnetic field, they can detect how the magnetic field correlates at their respective locations. Scientists use a technique called a Ramsey-type experiment to measure the unique local magnetic fields at each site. By analyzing the correlation between the signals from the two NV centers, it’s possible to identify common and distinct characteristics of the magnetic field.

Experiment with External Radiofrequency Coil

In one experiment, researchers applied a random phase ac signal to two shallow NV centers using an external radiofrequency coil. They were able to spatially separate the NV centers and independently excite and read their signals using separate optical paths. The scientists observed correlations in the spin state of the NV centers and confirmed that these correlations were genuine. The sensitivity of this method, called covariance measurement, is different from traditional magnetometry because it relies on simultaneous signals from two NV centers. Importance of Readout Fidelity The ability to detect correlations is heavily dependent on the quality of the readout or the process of extracting information from the NV centers. In single-NV center two-point correlators, reducing readout noise is essential for detecting correlations. A technique called shot-to-shot cross-correlation (SCC) readout substantially improves the detection of coincident events and has a more significant impact on covariance measurements compared to conventional single-NV center measurements. With SCC readout, readout noise is significantly reduced, making covariance magnetometry more practical to implement.

Revealing Hidden Information

Covariance magnetometry can help uncover hidden information about the spatial structure of noise by detecting cross-correlations in pure noise. This method can differentiate between correlated and uncorrelated noise sources, enabling researchers to analyze the spatial composition of the noise. By measuring the broadband correlation in the random phases of the decohered NV centers, hidden features in single-NV spectra can be revealed.

Applications and Future Extensions

Covariance magnetometry allows for the measurement of the temporal structure of two-point correlators separated in both time and space. To perform this measurement, independent control of each NV center is required, enabling direct assessment of time-domain structure on the nanosecond scale. This technique can be applied to any time-varying signal with a nonzero correlation time that can be detected with NV centers.

The study demonstrates the simultaneous control and readout of two spatially resolved NV centers for nanoscale magnetometry. This method can sense spatiotemporal correlations of any signal that can be imprinted as a phase on the NV centers. By measuring two-point correlators, valuable information about the underlying dynamics of fluctuating electromagnetic fields near surfaces can be obtained, providing insights into nonequilibrium transport dynamics and condensed matter phenomena. Future research may explore the use of photonic structures, different pulse sequences, additional NV centers, and detector arrays for simultaneous readout of multiple pairs of NV centers.

Required Additional Study Materials

• F. Casola, T. van der Sar, A. Yacoby, Probing condensed matter physics with magnetometry based on nitrogen-vacancy centres in diamond. Nat. Rev. Mater. 3, 17088 (2018).
• J. F. Barry, J. M. Schloss, E. Bauch, M. J. Turner, C. A. Hart, L. M. Pham, R. L. Walsworth, Sensitivity optimization for NV-diamond magnetometry. Rev. Mod. Phys. 92, 015004 (2020).
• D. A. Hopper, H. J. Shulevitz, L. C. Bassett, Spin readout techniques of the nitrogen-vacancy center in diamond. Micromachines 9, 437 (2018).
• C. L. Degen, F. Reinhard, P. Cappellaro, Quantum sensing. Rev. Mod. Phys. 89, 035002 (2017).
• P. Szańkowski, G. Ramon, J. Krzywda, D. Kwiatkowski, Ł. Cywiński, Environmental noise spectroscopy with qubits subjected to dynamical decoupling. J. Phys. Condens. Matter 29, 333001 (2017).

Introductory material

• “Quantum diamond sensors” by Neil Savage

Reference

SCIENCE 22 Dec 2022 Vol 378, Issue 6626 pp. 1301-1305 DOI: 10.1126/science.ade985

Three-dimensional nanofabrication via ultrafast laser patterning and kinetically regulated material assembly

• 3D Printing

Introduction to Multimaterial 3D Nanofabrication Challenges

Creating intricate 3D nanostructures with multiple materials is a difficult goal in nanotechnology due to the 88limited material choices88 and each material’s unique properties. Direct assembly through bottom-up processes, which build structures from the atomic or molecular level, offers a promising strategy. Hydrogels, capable of capturing materials through various interactions, provide a potential method for creating composites and supporting in situ photoreduction.

Hydrogel Patterning with Light Sheets

Researchers have developed a technique using femtosecond (fs) light sheets, which are ultrafast laser pulses, to modify a hydrogel’s polymeric network, allowing for the creation of complex 3D patterns from various materials. This method can be applied to water-dispersible materials with suitable sizes and hydrophilicity, achieving sub-diffraction limit resolution, which is essential for nano-device fabrication. The fabrication process involves pre-shrinking the hydrogel in hydrochloric acid before depositing material, which results in smaller features below the diffraction limit. Scanning electron microscopy (SEM) can then be used to study these features after material deposition and dehydration.

Laser Modification of Hydrogels

The new method for patterning hydrogels uses high-intensity laser light to modify the gel network directly, creating porous structures at the patterned sites. This process also changes the gel’s chemical composition, increasing the oxygen-to-carbon ratio and producing a new peak in Fourier-transform infrared (FTIR) spectra. The increased presence of hydroxyl groups enhances hydrogen bond formation, enabling selective attachment of materials to build 3D nanostructures.

Adaptable Fabrication Technique and Applications

The hydrogel-based fabrication method can be applied to materials with various properties, as demonstrated by depositing different nanoparticles into distinct animal shapes. This technique allows the creation of alloy structures without visible distortion at high shrinkage ratios. It also enables the fabrication of complex 3D structures with different materials and feature sizes, high patterning rates, and self-alignment for multilayer printing. The fabricated structures’ morphology can be retained in preshrunk hydrogels, as shown by the successful creation of a modified woodpile structure of gold-silver alloy.

Achievements in Resolution, Material Density, and Optical Storage

The researchers investigated the fabrication resolution of 2D and 3D nanostructures, achieving minimal feature sizes of $~25$ nm. The structures fabricated were highly reproducible, with average lateral and axial resolutions of $36.0 ± 5.1$ nm and $148.4 ± 19.2$ nm, respectively. Material density is crucial for evaluating fabricated structures, and atomic force microscopy (AFM) measurements showed high levels of smoothness in gold and silver structures, indicating high material density. The technique can be used to fabricate conductive microelectrodes and optical microdevices, such as diffractive optical elements. Additionally, the researchers developed an optical storage and encryption method using nanometer-level features and high laser patterning rates, achieving a storage density of $20$ terabits (Tb)/cm3 and a theoretical storage density of $~5$ petabits (Pbit)/cm$^3$.

In summary, the kinetic control-based fabrication method offers a versatile platform for creating complex 3D structures with a wide range of materials without the need for complicated chemistry or specialized printing setups. This innovative approach has the potential to impact various fields, including photonics, nanotechnology, and biotechnology, by enabling the creation of functional and biocompatible microdevices, optical metamaterials, and flexible electronics.

Required Additional Study Materials

• H. Zhao, Y. Lee, M. Han, B. K. Sharma, X. Chen, J.-H. Ahn, J. A. Rogers, Nanofabrication approaches for functional three-dimensional architectures. Nano Today30, 100825 (2020).
• J. F. Xing, M. L. Zheng, X. M. Duan, Two-photon polymerization microfabrication of hydrogels: An advanced 3D printing technology for tissue engineering and drug delivery. Chem. Soc. Rev.44, 5031–5039 (2015).
• Y. L. Zhang, Q. D. Chen, H. Xia, H. B. Sun, Designable 3D nanofabrication by femtosecond laser direct writing. Nano Today5, 435–448 (2010).
• C. Barner-Kowollik, M. Bastmeyer, E. Blasco, G. Delaittre, P. Müller, B. Richter, M. Wegener, 3D Laser Micro- and Nanoprinting: Challenges for Chemistry. Angew. Chem. Int. Ed.56, 15828–15845 (2017).
• J. Li, E. H. Hill, L. Lin, Y. Zheng, Optical Nanoprinting of Colloidal Particles and Functional Structures. ACS Nano13, 3783–3795 (2019).
• S. Soleymani, Eil, Bakhtiariet al., 3‐Dimensional Printing of Hydrogel‐Based Nanocomposites: A Comprehensive Review on the Technology Description, Properties, and Applications. Adv. Eng. Mater.23, 2100477 (2021).
• S. Pradhan, K. A. Keller, J. L. Sperduto, J. H. Slater, Fundamentals of Laser-Based Hydrogel Degradation and Applications in Cell and Tissue Engineering. Adv. Healthc. Mater.6, 1700681 (2017).
• Y. Wang, J. He, C. Liu, W. H. Chong, H. Chen, Thermodynamics versus kinetics in nanosynthesis. Angew. Chem. Int. Ed.54, 2022–2051 (2015).

Introductory material

• “Ultrafast Lasers: A Comprehensive Introduction to Fundamental Principles with Practical Applications” by Ursula Keller
• “Ultrafast Laser Nanostructuring: The Pursuit of Extreme Scales” by Razvan Stoian and Jörn Bonse

Reference

SCIENCE 22 Dec 2022 Vol 378, Issue 6626 pp. 1325-1331 DOI: 10.1126/science.abm8420

Ionocaloric refrigeration cycle

• Calorics

Addressing the Environmental Concerns of Traditional Refrigeration

Traditional vapor-compression refrigeration relies on hydrofluorocarbons (HFCs), which have a high global warming potential. Researchers are exploring environmentally-friendly alternatives, such as solid-state materials that provide a refrigeration effect when an external field is applied. The ionocaloric effect, a newly discovered caloric effect, induces an entropy change through the electrochemical mixing of species and has shown better performance than other caloric materials.

Fundamentals of the Ionocaloric Effect

The ionocaloric effect involves adding ions to a solid, which lowers its melting point and causes it to melt and release energy. This can be used for a different kind of refrigeration called electrochemical refrigeration. In this approach, a first-order phase transition in the solvent allows for significant changes in entropy and temperature. The ionocaloric effect can cool or heat a material depending on whether an electrochemical field is applied or removed.

Characteristics of an Ideal Ionocaloric Material

For continuous refrigeration, the ionocaloric effect must be incorporated into an appropriate thermodynamic cycle. An ideal ionocaloric material should have a melting point above room temperature, a eutectic transition well below room temperature, and a high enthalpy of fusion. The ethylene carbonate (EC)-sodium iodide (NaI) system is a promising candidate, featuring a melting point of $36.4$°C, a eutectic transition at $6.4$°C, and a high latent heat of fusion of $204.6$ J mL$^{−1}$.

Developing a Practical Ionocaloric Device

The EC-NaI system has favorable theoretical properties for caloric materials, but its practical performance is determined by the efficiency of the separation process. Various desalination technologies, such as thermal, mechanical, and electrochemical techniques, can be used for this purpose. In this study, electrodialysis was chosen because it operates efficiently without the need for high pressures or fields. Electrodialysis separates ions by applying an electric field across ion-exchange membranes, and the experimental coefficient of performance (COP) was calculated from the work input and the cooling energy provided.

Performance and Potential Improvements

The ionocaloric device outperforms other caloric devices, delivering a cooling power of $5.75$ W L$^{−1}$ and operating at $29.5\%$ of Carnot efficiency with a temperature span of $25.76$°C. However, the cooling power output is lower than electrocaloric devices due to the membrane resistance of the EC-NaI electrolyte. To increase the cooling power density of ionocaloric devices, low-resistance membranes specifically designed for organic electrolytes need to be developed.

Electrodialysis can help reduce the strength of the applied field needed, lowering the cost of refrigeration technology based on the ionocaloric cycle. The ionocaloric effect shows great promise in achieving higher performance compared to other caloric materials in terms of COP, temperature lift, and power density, with further improvements possible. This environmentally-friendly refrigeration alternative has the potential to make a significant impact in the field.

Required Additional Study Materials

• M. O. McLinden, C. J. Seeton, A. Pearson, New refrigerants and system configurations for vapor-compression refrigeration. Science370, 791–796 (2020).
• A. Greco, C. Aprea, A. Maiorino, C. Masselli, A review of the state of the art of solid-state caloric cooling processes at room-temperature before 2019. Int. J. Refrig.106, 66–88 (2019).
• P. Lloveras, J.-L. Tamarit, Advances and obstacles in pressure-driven solid-state cooling: A review of barocaloric materials. MRS Energy Sustain.8, 3–15 (2021).
• A. Chauhan, S. Patel, R. Vaish, C. R. Bowen, A review and analysis of the elasto-caloric effect for solidstate refrigeration devices: Challenges and opportunities. MRS Energy Sustain.2, 16 (2015).
• N. R. Ram, M. Prakash, U. Naresh, N. S. Kumar, T. S. Sarmash, T. Subbarao, R. J. Kumar, G. R. Kumar, K. C. B. Naidu, Review on Magnetocaloric Effect and Materials. J. Supercond. Nov. Magn.31, 1971–1979 (2018).
• J. R. Rumble, CRC Handbook of Chemistry and Physics (CRC Press, ed. 102, 2021).
• A. Torelló, E. Defay, Electrocaloric Coolers: A Review. Adv. Electron. Mater.8, 2101031 (2022).
• J. Lyubina, Magnetocaloric materials for energy efficient cooling. J. Phys. D Appl. Phys.50, 053002 (2017).
• H. Hou, S. Qian, I. Takeuchi, Materials, physics and systems for multicaloric cooling. Nat. Rev. Mater.7, 633–652 (2022).

Introductory material

• “Present and future caloric refrigeration and heat-pump technologies” by Andrej Kitanovski et al.

Reference

SCIENCE 22 Dec 2022 Vol 378, Issue 6626 pp. 1344-1348 DOI: 10.1126/science.ade1696