Balancing Energy-Level Difference for Efficient n-i-p Perovskite Solar Cells with Cu Electrode

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Journal profile

The Open Access journal Energy Material Advances, published in association with BIT, is an interdisciplinary platform for research in multiple fields from cutting-edge material to energy science.

Editorial board

Energy Material Advances’ editorial board is led by Feng Wu (Beijing Institute of Technology) and Jun Liu (University of Washington) and is comprised of experts who have made significant and well recognized contributions to the field.

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Research Article

Unraveling the Effect of Cation Types on Electrochromic Properties of Titanium Dioxide Nanocrystals

Electrochromic (EC) devices have been regarded as promising candidates for energy-saving smart windows, next-generation displays, and wearable electronics. Monovalent ions such as H+- and Li+-based electrolytes are the benchmark insertion ions for EC devices but have serious limitations such as high cost, instability, and difficulty to handle. Seeking multivalent electrolytes is an effective alternative way to prepare high-performance EC devices; unfortunately, the related reports are currently limited to tungsten oxide EC materials. Herein, for the first time, we investigate the EC properties driven by different valence cationic (i.e., Li+, Zn2+, and Al3+) electrolytes in the titanium dioxide system. It is found that the initial optical modulation ranges of TiO2 nanocrystal (NC) films in Li+, Zn2+, and Al3+ electrolytes are 76.8%, 77.4%, and 77.3%, respectively. After 250 cycles, the optical contrast of these films in Zn2+ electrolyte decreased by only 2.3%, much lower than that in benchmark Li+ electrolyte of 10.1% and Al3+ electrolyte of 59.1%. Density functional theory calculation indicates that the potential barriers of Li+, Zn2+, and Al3+ in TiO2 are 0.59, 0.55, and 0.74 eV, respectively, which makes TiO2 NCs show good EC properties in Zn2+ electrolytes. This work unravels the effect of different valence cations on the electrochromic properties of titanium dioxide NCs, which may provide some new directions for the development of excellent EC devices with long-term stability and durability.

Review Article

Recent Development of Integrated Systems of Microsupercapacitors

Development of wearable and portable electronics promotes the miniaturization of energy storage devices. Microsupercapacitor (MSC) featuring in fast charging and discharging rates, long cycle life, and high-power density stands out from miniaturized energy storage devices, particularly for its small size and adjustable structure which is easily processed to integrate with other on-chip electronics. In this review, we systematically analyzed the MSC integration with other electronics from the perspective of structures and functions. At the beginning, we briefly introduced typical MSCs with unique properties. Subsequently, applications and integrations of MSCs with energy-consuming or energy-generating electronics were highlighted. Furthermore, compatible materials and designed structure of the all-in-one device were also depicted. Finally, challenges and future development of MSC-integrated systems were put forward.

Research Article

Balancing Energy-Level Difference for Efficient n-i-p Perovskite Solar Cells with Cu Electrode

Developing low cost and stable metal electrode is crucial for mass production of perovskite solar cells (PSCs). As an earth-abundant element, Cu becomes an alternative candidate to replace noble metal electrodes such as Au and Ag, due to its comparable physiochemical properties with simultaneously good stability and low cost. However, the undesirable band alignment associated with the device architecture impedes the exploration of efficient Cu-based n-i-p PSCs. Here, we demonstrated the ability of tuning the Fermi level () of hole transport layer (HTL) to reduce the energy level difference (Schottky barrier) between HTLs and Cu. Further, we identified that the balance of energy level difference between HTL and adjacent layers (including perovskite and Cu) is crucial to efficient carrier transportation and photovoltaic performance improvement in the PSCs. Under the optimized condition, we achieve a device power conversion efficiency (PCE) of 20.10%, which is the highest on the planar n-i-p PSCs with Cu electrode. Meanwhile, the Cu-based PSCs can maintain 92% of their initial efficiency after 1000 h storage, which is comparable with Au-based devices. The present work not only extends the understanding on the band alignment of neighboring semiconductor functional layer in the device architecture to improve the resulting performance but also suggests great potential of Cu electrode for application in PSCs community.

Review Article

Air/Water Stability Problems and Solutions for Lithium Batteries

Recently, lithium-ion batteries (LIBs) have faced bottlenecks in terms of energy/power density and safety issues caused by flammable electrolytes. In this regard, all-solid-state batteries (ASSBs) may be one of the most promising solutions. However, many key battery materials (such as solid electrolytes (SEs), cathodes, and anodes) are unstable to air/water, which greatly limits their production, storage, transportation, practical applications, and the development of ASSBs. Herein, the research status on air/water stability of SEs, cathodes, and anodes is reviewed. The mechanisms for their air/water instability are revealed in details. The corresponding modification methods are also proposed, with emphasis on the construction strategies of air/water stable protective layers, including ex situ coatings and in situ reactions. Moreover, the application of air/water-stable protective layers in ASSBs is discussed correspondingly. Last but not least, the advantages and disadvantages of various protective layer construction strategies are analyzed, in which their applications in practical production are prospected.

Research Article

20 μm-Thick Li6.4La3Zr1.4Ta0.6O12-Based Flexible Solid Electrolytes for All-Solid-State Lithium Batteries

The doped garnet-type solid electrolytes are attracting great interest due to high ionic conductivity and excellent electrochemical stability against Li metal. However, the thick electrolyte layer and rigid nature as well as poor interfacial contact are huge obstacles for its application in all-solid-state lithium batteries. Herein, an ultrathin flexible Li6.4La3Zr1.4Ta0.6O12- (LLZTO-) based solid electrolyte with 90 wt% LLZTO content is realized through solvent-free procedure. The resultant 20 μm-thick LLZTO-based film exhibits ultrahigh ionic conductance of 41.21 mS at 30°C, excellent oxidation stability of 4.6 V, superior thermal stability and nonflammability. Moreover, the corresponding Li||Li symmetric cell can stable cycle for more than 2000 h with low overpotential at 0.1 mA cm-2 under 60°C. The assembled Li||LiFePO4 pouch cell with integrated electrolyte/cathode interface exhibits excellent rate performances and cycle performances with a capacity retention of 71.4% from 153 mAh g-1 to 109.2 mAh g-1 at 0.1 C over 500 cycles under 60°C. This work provides a promising strategy towards realizing ultrathin flexible solid electrolyte for high-performance all-solid-state lithium batteries.

Research Article

Crystal Facet-Dependent Intrinsic Charge Separation on Well-Defined Bi4TaO8Cl Nanoplate for Efficient Photocatalytic Water Oxidation

The development of photocatalysts with wide spectral absorption and high charge separation efficiency has always been a pursued objective for photocatalytic solar energy conversion. Herein, we reported a wide-range visible-light-active Bi4TaO8Cl (BTOC) single crystal nanoplate with dominating {110} and {001} facets for enhancing the intrinsic charge separation efficiency. Insitu selective photodeposition of metals and metal oxides provides evidences of photogenerated electrons and holes spatially separated on {110} and {001} coexposed facets of BTOC, respectively. The intrinsic charge separation efficiency was demonstrated to be closely dependent on the crystal facets, which can be modulated by tuning the coexposed crystal facet ratio. Further surface modification of BTOC with suitable dual cocatalyst Ag and RuOx enables remarkable improvement of charge separation efficiency and photocatalytic water oxidation performance. Investigation by comparison between well-defined BTOC nanoplate and BTOC nanoparticles confirmed the significance of coexposed crystal facets for efficient spatial charge separation and the blocking of reverse reaction from Fe2+ to Fe3+ ions during water oxidation reaction, indicating that rational modulation of exposed crystal facets is significant for controlling the intrinsic charge separation efficiency on Bi4TaO8Cl photocatalyst for efficient photocatalytic water splitting.