The power conversion efficiency of perovskite solar cells (PSCs) has ascended from 3.8% to 22.1% in recent years. ZnO has been well‐documented as an excellent electron‐transport material. However, ...the poor chemical compatibility between ZnO and organo‐metal halide perovskite makes it highly challenging to obtain highly efficient and stable PSCs using ZnO as the electron‐transport layer. It is demonstrated in this work that the surface passivation of ZnO by a thin layer of MgO and protonated ethanolamine (EA) readily makes ZnO as a very promising electron‐transporting material for creating hysteresis‐free, efficient, and stable PSCs. Systematic studies in this work reveal several important roles of the modification: (i) MgO inhibits the interfacial charge recombination, and thus enhances cell performance and stability; (ii) the protonated EA promotes the effective electron transport from perovskite to ZnO, further fully eliminating PSCs hysteresis; (iii) the modification makes ZnO compatible with perovskite, nicely resolving the instability of ZnO/perovskite interface. With all these findings, PSCs with the best efficiency up to 21.1% and no hysteresis are successfully fabricated. PSCs stable in air for more than 300 h are achieved when graphene is used to further encapsulate the cells.
Surface passivation of ZnO by a thin layer of MgO and protonated ethanolamine readily makes ZnO a very promising electron‐transporting material for creating efficient, hysteresis‐free and stable perovskite solar cells (PSCs). PSCs, stable in air for more than 300 h, are achieved when graphene is used to encapsulate the cells.
Dendrite growth of alkali metal anodes limited their lifetime for charge/discharge cycling. Here, we report near-perfect anodes of lithium, sodium, and potassium metals achieved by electrochemical ...polishing, which removes microscopic defects and creates ultra-smooth ultra-thin solid-electrolyte interphase layers at metal surfaces for providing a homogeneous environment. Precise characterizations by AFM force probing with corroborative in-depth XPS profile analysis reveal that the ultra-smooth ultra-thin solid-electrolyte interphase can be designed to have alternating inorganic-rich and organic-rich/mixed multi-layered structure, which offers mechanical property of coupled rigidity and elasticity. The polished metal anodes exhibit significantly enhanced cycling stability, specifically the lithium anodes can cycle for over 200 times at a real current density of 2 mA cm
with 100% depth of discharge. Our work illustrates that an ultra-smooth ultra-thin solid-electrolyte interphase may be robust enough to suppress dendrite growth and thus serve as an initial layer for further improved protection of alkali metal anodes.
Electrochemical water splitting is a common way to produce hydrogen gas, but the sluggish kinetics of the oxygen evolution reaction (OER) significantly limits the overall energy conversion efficiency ...of water splitting. In this work, a highly active and stable, meso–macro hierarchical porous Ni3S4 architecture, enriched in Ni3+ is designed as an advanced electrocatalyst for OER. The obtained Ni3S4 architectures exhibit a relatively low overpotential of 257 mV at 10 mA cm−2 and 300 mV at 50 mA cm−2. Additionally, this Ni3S4 catalyst has excellent long‐term stability (no degradation after 300 h at 50 mA cm−2). The outstanding OER performance is due to the high concentration of Ni3+ and the meso–macro hierarchical porous structure. The presence of Ni3+ enhances the chemisorption of OH−, which facilitates electron transfer to the surface during OER. The hierarchical porosity increases the number of exposed active sites, and facilitates mass transport. A water‐splitting electrolyzer using the prepared Ni3S4 as the anode catalyst and Pt/C as the cathode catalyst achieves a low cell voltage of 1.51 V at 10 mA cm−2. Therefore, this work provides a new strategy for the rational design of highly active OER electrocatalysts with high valence Ni3+ and hierarchical porous architectures.
The Ni3S4 enriched with high‐valence Ni3+ enhances the chemisorption of OH−, which facilitates electron transfer from the OH− to the surface Ni sites during the oxygen evolution reaction. The hierarchical porous structure enables a high number of active sites and faster mass transfer.
Sodium metal anodes are poor due to the reversibility of Na plating/stripping, which hinders their practical applications. A strategy to form a sodiophilic Au–Na alloy interphase on a Cu current ...collector, involving a sputtered Au thin layer, is shown to enable efficient Na plating/stripping for a certain period of time. Herein, electrochemical behaviors of Na plating on different substrates are explored, and it is revealed that the sodiophilic interphase can be achieved universally by in situ formation of M–Na (M = Au, Sn, and Sb) alloys during Na plating prior to Na bulk deposition in the initial cycle. Moreover, it is found that repetitive alloying–dealloying leads to falling‐off of thin film sodiophilic materials and thus limits the lifespan of efficient Na cycling. Therefore, an approach is further developed by employing particles of sodiophilic materials combined with the control over the cutoff potential, which significantly improves the stability of Na plating/stripping process. Especially, the low‐cost Cu@Sn‐NPs and Cu@Sb‐MPs composite current collectors allow Na plating and stripping to cycle for 2000 and 1700 times with the average efficiency of 99.9% at 2 mA cm−2.
Stable Na plating/stripping electrochemical behaviors are achieved by using the in situ formed sodiophilic sodium‐metal (metal = Au, Sn, Sb) alloy interphase. By simultaneous control over the stripping cut‐off potential and employment of anchored metal particles, Na plating/stripping cycling is extended to 2000 times at 2 mA cm−2 with an average Coulombic efficiency of 99.9% on the sodium‐metal alloy‐based interphase.
Solid state potassium (K) metal batteries are intriguing in grid‐scale energy storage, benefiting from the low cost, safety, and high energy density. However, their practical applications are impeded ...by poor K/solid electrolyte (SE) interfacial contact and limited capacity caused by the low K self‐diffusion coefficient, dendrite growth, and intrinsically low melting point/soft features of metallic K. Herein, a fused‐modeling strategy using potassiophilic carbon allotropes molted with K is demonstrated that can enhance the electrochemical performance/stability of the system via promoting K diffusion kinetics (2.37 × 10−8 cm2 s−1), creating a low interfacial resistance (≈1.3 Ω cm2), suppressing dendrite growth, and maintaining mechanical/thermal stability at 200 °C. A homogeneous/stable K stripping/plating is consequently implemented with a high current density of 2.8 mA cm−2 (at 25 °C) and a record‐high areal capacity of 11.86 mAh cm−2 (at 0.2 mA cm−2). The enhanced K diffusion kinetics contribute to sustaining intimate interfacial contact, stabilizing the stripping/plating at high current densities. Full cells coupling ultrathin K–C composite anodes (≈50 µm) with Prussian blue cathodes and β/β″‐Al2O3 SEs deliver a high energy density of 389 Wh kg−1 with a retention of 94.4% after 150 cycles and fantastic performances at −20 to 120 °C.
An ultrathin K–10% reduced graphene oxide anode is constructed, delivering promoted K diffusion kinetics and mechanical/thermal stability at 200 °C, which creates an interfacial resistance (≈1.3 Ω cm2) with a current density of 2.8 mA cm−2 at 25 °C and an areal capacity of 11.86 mAh cm−2, enabling solid state potassium metal batteries operating at −20 to 120 °C.
Witnessed by the rapid increase of power conversion efficiency to 25.5%, organic–inorganic hybrid perovskite solar cells (PSCs) are becoming promising candidates of next‐generation photovoltaics. ...However, PSCs can be unstable under the influence of light and bias. Especially, grain boundaries (GBs) are vulnerable to attack by light and bias in perovskite films, leading to degradation of photovoltaic properties of PSCs. Herein, photocurrent atomic force microscopy and Kelvin probe force microscopy are employed to systematically investigate the bias‐dependent charge transport behaviors and stability of (FAPbI3)0.85(MAPbBr3)0.15 perovskite under working condition. Bias‐dependent morphology and photocurrent images show irreversible decomposition of the perovskite at a bias of 0.1 V or below, which is accelerated by light illumination, leading to formation of an interfacial layer that restricts carrier transport. Meanwhile, GBs appear to enhance carrier transport at larger bias, but serve as breakthrough sites for perovskite decomposition at smaller bias. Introducing excess methylammonium iodide promotes decomposition, while potassium iodide passivation greatly relieves the decomposition. These results support the ion migration mechanism of decomposition through interfaces and GBs. This work provides a deeper understanding of bias‐induced degradation of PSCs as well as bias‐dependent double‐edged roles of GBs, and forms valuable guidance for appropriate operation of PSCs.
Bias‐dependent stability of (FAPbI3)0.85(MAPbBr3)0.15 perovskite and double‐edged roles of grain boundaries in carrier transport and degradation of solar cells under working condition are systematically investigated. Photocurrent atomic force microscopy results show that grain boundaries enhance carrier transport at larger bias, but serve as breakthrough sites at smaller bias of 0.1 V or below when irreversible decomposition of perovskite occurs.
Abstract
Electrochemical water splitting is a common way to produce hydrogen gas, but the sluggish kinetics of the oxygen evolution reaction (OER) significantly limits the overall energy conversion ...efficiency of water splitting. In this work, a highly active and stable, meso–macro hierarchical porous Ni
3
S
4
architecture, enriched in Ni
3+
is designed as an advanced electrocatalyst for OER. The obtained Ni
3
S
4
architectures exhibit a relatively low overpotential of 257 mV at 10 mA cm
−2
and 300 mV at 50 mA cm
−2
. Additionally, this Ni
3
S
4
catalyst has excellent long‐term stability (no degradation after 300 h at 50 mA cm
−2
). The outstanding OER performance is due to the high concentration of Ni
3+
and the meso–macro hierarchical porous structure. The presence of Ni
3+
enhances the chemisorption of OH
−
, which facilitates electron transfer to the surface during OER. The hierarchical porosity increases the number of exposed active sites, and facilitates mass transport. A water‐splitting electrolyzer using the prepared Ni
3
S
4
as the anode catalyst and Pt/C as the cathode catalyst achieves a low cell voltage of 1.51 V at 10 mA cm
−2
. Therefore, this work provides a new strategy for the rational design of highly active OER electrocatalysts with high valence Ni
3+
and hierarchical porous architectures.
In a modern electronics system, charge‐coupled devices and data storage devices are the two most indispensable components. Although there has been rapid and independent progress in their development ...during the last three decades, a cofunctionality of both sensing and memory at single‐unit level is yet premature for flexible electronics. For wearable electronics that work in ultralow power conditions and involve strains, conventional sensing‐and‐memory systems suffer from low sensitivity and are not able to directly transform sensed information into sufficient memory. Here, a new transformative device is demonstrated, which is called “sen‐memory”, that exhibits the dual functionality of sensing and memory in a monolithic integrated circuit. The active channel of the device is formed by a carbon nanotube thin film and the floating gate is formed by a controllably oxidized aluminum nanoparticle array for electrical‐ and optical‐programming. The device exhibits a high on–off current ratio of ≈106, a long‐term retention of ≈108 s, and durable flexibility at a bending strain of 0.4%. It is shown that the device senses a photogenerated pattern in seconds at zero bias and memorizes an image for a couple of years.
Transformative nanodevices incorporate emerging nanotechnologies to meet future data‐intensive applications. A new flexible carbon nanotube transformative device named “sen‐memory” is developed, showing fused sensing‐and‐memory functionality and large scalability. The sen‐memory matrix realizes an in situ writing of optical data into nonvolatile memory without an auxiliary gate bias and the photogenerated pattern can be stored for a couple of years.
The spontaneous α-to-δ phase transition of the formamidinium-based (FA) lead halide perovskite hinders its large scale application in solar cells. Though this phase transition can be inhibited by ...alloying with methylammonium-based (MA) perovskite, the underlying mechanism is largely unexplored. In this Communication, we grow high-quality mixed cations and halides perovskite single crystals (FAPbI3)1–x (MAPbBr3) x to understand the principles for maintaining pure perovskite phase, which is essential to device optimization. We demonstrate that the best composition for a perfect α-phase perovskite without segregation is x = 0.1–0.15, and such a mixed perovskite exhibits carrier lifetime as long as 11.0 μs, which is over 20 times of that of FAPbI3 single crystal. Powder XRD, single crystal XRD and FT-IR results reveal that the incorporation of MA+ is critical for tuning the effective Goldschmidt tolerance factor toward the ideal value of 1 and lowering the Gibbs free energy via unit cell contraction and cation disorder. Moreover, we find that Br incorporation can effectively control the perovskite crystallization kinetics and reduce defect density to acquire high-quality single crystals with significant inhibition of δ-phase. These findings benefit the understanding of α-phase stabilization behavior, and have led to fabrication of perovskite solar cells with highest efficiency of 19.9% via solvent management.
Traditional coupling of ligands for gold wet etching makes large-scale applications problematic. Deep eutectic solvents (DESs) are a new class of environment-friendly solvents, which could possibly ...overcome the shortcomings. In this work, the effect of water content on the Au anodic process in DES ethaline was investigated by combining linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). Meanwhile, we employed atomic force microscopy (AFM) to image the evolution of the surface morphology of the Au electrode during its dissolution and passivation process. The obtained AFM data help to explain the observations about the effect of water content on the Au anodic process from the microscopic perspective. High water contents make the occurrence of anodic dissolution of gold at higher potential, but enhances the rate of the electron transfer and gold dissolution. AFM results reveal the occurrence of massive exfoliation, which confirms that the gold dissolution reaction is more violent in ethaline with higher water contents. In addition, AFM results illustrate that the passive film and its average roughness could be tailored by changing the water content of ethaline.
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