Prussian blue analogs (PBAs) are especially investigated as superior cathodes for sodium‐ion batteries (SIBs) due to high theoretical capacity (≈170 mA h g−1) with 2‐Na storage and low cost. However, PBAs suffer poor cyclability due to irreversible phase transition in deep charge/discharge states. PBAs also suffer low crystallinity, with considerable [Fe(CN)6] vacancies, and coordinated water in crystal frameworks. Presently, a new chelating agent/surfactant coassisted crystallization method is developed to prepare high‐quality (HQ) ternary‐metal NixCo1−x[Fe(CN)6] PBAs. By introducing inactive metal Ni to suppress capacity fading caused by excessive lattice distortion, these PBAs have tunable limits on depth of charge/discharge. HQ‐NixCo1−x[Fe(CN)6] (x = 0.3) demonstrates the best reversible Na‐storage behavior with a specific capacity of ≈145 mA h g−1 and a remarkably improved cycle performance, with ≈90% capacity retention over 600 cycles at 5 C. Furthermore, a dual‐insertion full cell on the cathode and NaTi2(PO4)3 anode delivers reversible capacity of ≈110 mA h g−1 at a current rate of 1.0 C without capacity fading over 300 cycles, showing promise as a high‐performance SIB for large‐scale energy‐storage systems. The ultrastable cyclability achieved in the lab and explained herein is far beyond that of any previously reported PBA‐based full cells.

Halide perovskite solar cells (PSCs) have drawn worldwide attention due to their great potential to be promising candidates for highly efficient and cost-effective photovoltaic technologies. [1] Benefiting from the excellent optoelectronic properties of halide perovskites together with previous abundant experience in other solar cells, especially in dye-sensitized solar cells and organic solar cells, the power conversion efficiency (PCE) of conventional PSCs has been boosted to 25.5%, [2] making PSCs one of the most efficient solar cell type. Conventional efficient PSCs in lab usually rely on costly materials such as gold or silver electrode and organic hole transport materials (HTM). [3] To further reduce the material and fabrication cost of PSCs toward commercialization, carbon electrode-based HTM-free perovskite solar cells (C-PSCs) are developed. [4] In C-PSCs, carbon electrodes (CEs) are chosen to replace metal electrodes due to their excellent adjustable electronic properties, chemical stability and low cost. [5] However, the efficiency of C-PSCs has not exceeded 20%. [6] Therefore, developing carbon materials for C-PSCs to promote their efficiency toward the comparable level as conventional PSCs is in great demand. [4] Since no additional HTM is applied in C-PSCs, adjusting the work function (WF) of CEs to realize more efficient hole extraction and more suitable energy level alignment is an effective strategy to enhance the efficiency of C-PSCs. [7,8] To realize this, Jiang et al. introduced p-type metal oxides into the CE to improve its WF for extracting holes. [9] However, the introduction of those metal oxides led to the sheet resistance increase of CEs, which resulted in series resistance increase of the C-PSCs and restricted the efficiency improvement. Doping graphite has been demonstrated as another effective method to adjust the CEs WF for improving C-PSCs performance. Duan et al. improved the efficiency of C-PSCs from 12.4% to 13.6% by applying boron-doped carbon as the electrode. [5] Yang's group improved the WF of CE and the efficiency of C-PSCs by doping graphite with boron. [10] In addition, it is found that introducing oxygen-containing functional groups into the CE can also increase the WF. Tian et al. synthesized a carbon black with much higher oxygen content and a much higher WF than common carbon black. [11] When applying it in the CE for C-PSCs, the device efficiency was enhanced from 13.6% to 15.7%. This work demonstrated that introducing oxygen into CEs is of great potential to improve C-PSCs efficiency. However, the restriction is that the related process for introducing oxygen is carried out at high temperature of about 1600 K. Therefore, developing facile methods to synthesize oxygen-rich carbon materials sustainably for CEs is worth exploring.Biomass materials, which hold the "Sustainable and green" characteristics, have been applied for different energy conversion devices. [12][13][14] Zhu et al. synthesized a ZrO 2 @cellulose acetatereinforced nanofibrous membrane for sodium-ion b...

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A new series of low-viscosity tetramethylguanidinum-based ionic liquids (ILs) with various substituted phenolate anions were prepared and characterized using nuclear magnetic resonance and Fourier transform irnfrared spectroscopy, elemental analysis, differential scanning calorimetry analysis, and thermogravimetry. Their densities, viscosities, refractive indices, and electrical conductivities were measured and correlated with thermodynamic and empirical equations in the temperature range of (298.15 to 343.15) K under ambient conditions. The effects of substituent groups in phenolate anions on these physical properties were then discussed on the basis of structure. Furthermore, the thermal expansion coefficient was calculated from the experimental values of density, and the correlation between the viscosity and the molar conductivity was proposed by the Walden rule. These ILs are classified as “poor ionic liquids” and have a poor temperature dependency of the thermal expansion coefficient.

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The power conversion efficiency (PCE) of single-junction perovskite solar cells (PSCs) is being rapidly promoted towards their theoretical limit, with a certified value of 25.7%. Reducing optical loss will further contribute to PCE improvement. Here, the optical loss including reflection loss, absorption loss, and transmission loss in printable mesoscopic perovskite solar cells (p-MPSCs) is analyzed. A printable mesoporous SiO 2 antireflection coating for improving the transmittance of the fluorine-doped tin oxide (FTO) glass substrate by reducing optical reflection at the air/glass interface is reported. With modulated porosity and thickness, the mesoporous SiO 2 film constructs a graded refractive index interface and increases the transmittance of FTO glass by ≈2%-4% in the spectral range of 350-800 nm at normal incident angle with the highest transmittance improved from 85% to 89%. The SiO 2 coating also exhibits wide-angle and broadband antireflection properties. The coatings successfully help p-MPSCs obtain about an average 3% enhancement in the short-circuit current density (J SC ) and PCE. This study demonstrates the necessity of optical management for efficient solar cells and provides a cost-effective and scalable antireflection coating for the future realistic application of PSCs.

Hole‐conductor‐free fully printable mesoscopic perovskite solar cells (MPSCs) based on mp‐TiO2/mp‐ZrO2/carbon triple mesoscopic layers are competitive candidates among various rapidly developed PSCs for future photovoltaic applications due to the characteristics of low‐cost, easy upscaling, and superior stability. However, the open‐circuit voltage (VOC) loss in printable MPSCs is relatively large compared to that in conventional PSCs, deteriorating the power conversion efficiency (PCE). Herein, the VOC loss is reduced by the octyltrimethylammonium chloride (OTAC) additive. OTAC is found to upshift the Fermi level of TiO2 and passivate trap states in bulk MAPbI3 perovskite, thus optimizing the energy‐level alignment of the TiO2/perovskite heterojunction and suppressing nonradiative recombination in devices. As a result, MPSCs deliver the highest PCE of 16.53% with an improved VOC of 1007 mV. The work demonstrates a facile strategy to reduce the VOC loss in printable MPSCs by simultaneously optimizing the energy‐level alignment and suppressing nonradiative recombination.

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