Induced Infiltration of Hole-Transporting Polymer into Photocatalyst for Staunch Polymer–Metal Oxide Hybrid Solar Cells

For efficient solar cells based on organic semiconductors, a good mixture of photoactive materials in the bulk heterojunction on the length scale of several tens of nanometers is an important requirement to prevent exciton recombination. Herein, we demonstrate that nanoporous titanium dioxide inverse opal structures fabricated using a self-assembled monolayer method and with enhanced infiltration of electron-donating polymers is an efficient electron-extracting layer, which enhances the photovoltaic performance. A calcination process generates an inverse opal structure of titanium dioxide (<70 nm of pore diameters) providing three-dimensional (3D) electron transport pathways. Hole-transporting polymers was successfully infiltrated into the pores of the surface-modified titanium dioxide under vacuum conditions at 200 °C. The resulting geometry expands the interfacial area between hole- and electron-transport materials, increasing the thickness of the active layer. The controlled polymer-coating process over titanium dioxide materials enhanced photocurrent of the solar cell device. Density functional theory calculations show improved interfacial adhesion between the self-assembled monolayer-modified surface and polymer molecules, supporting the experimental result of enhanced polymer infiltration into the voids. These results suggest that the 3D inverse opal structure of the surface-modified titanium dioxide can serve as a favorable electron-extracting layer in further enhancing optoelectronic performance based on organic or organic–inorganic hybrid solar cell

Self-Terminated Artificial SEI Layer for Nickel-Rich Layered Cathode Material via Mixed Gas Chemical Vapor Deposition

Because of the higher specific capacity, nickel-rich layered cathode material has received much attention from the lithium-ion battery community. However, its cycle life is desired to improve further for practical applications, and unstable interface with electrolyte is one of the main capacity fading mechanisms. Here, we report a facile chemical vapor deposition process involving mixed gases of CO₂ and CH₄, which yields thin and conformal artificial solid-electrolyte-interphase (SEI) layer consisting of alkyl lithium carbonate (LiCO₃R) and lithium carbonate (Li₂CO₃) on nickel-rich active cathode powder. The coating layer protects from side reactions and improves the cycle life and efficiency significantly. Remarkably, the coating process is self-terminated after the thickness reaches ∼10 nm, leading to the coating layer to account for only 0.48 wt %, because of the growing binding energy between the gas mixture and the surface products. The self-termination is characterized by various analytical tools and is well-explained by density functional theory calculations. The current gas phase coating process should be applicable to other battery materials that suffer from continuous side reactions with electrolyte

Dendrite-Free Polygonal Sodium Deposition with Excellent Interfacial Stability in a NaAlCl₄–2SO₂ Inorganic Electrolyte

Room-temperature Na-metal-based rechargeable batteries, including Na–O₂ and Na–S systems, have attracted attention due to their high energy density and the abundance of sodium resources. Although these systems show considerable promise, concerns regarding the use of Na metal should be addressed for their success. Here, we report dendrite-free Na-metal electrode for a Na rechargeable battery, engineered by employing nonflammable and highly Na⁺-conductive NaAlCl₄·2SO₂ inorganic electrolyte, as a result, showing superior electrochemical performances to those in conventional organic electrolytes. We have achieved a hard-to-acquire combination of nondendritic Na electrodeposition and highly stable solid electrolyte interphase at the Na-metal electrode, enabled by inducing polygonal growth of Na deposit using a highly concentrated Na⁺-conducting inorganic electrolyte and also creating highly dense passivation film mainly composed of NaCl on the surface of Na-metal electrode. These results are highly encouraging in the development of room-temperature Na rechargeable battery and provide another strategy for highly reliable Na-metal-based rechargeable batteries

CO₂ Enhanced Chemical Vapor Deposition Growth of Few-Layer Graphene over NiO_<i>x</i>

The use of mild oxidants in chemical vapor deposition (CVD) reactions has proven enormously useful. This was also true for the CVD growth of carbon nanotubes. As yet though, the use of mild oxidants in the CVD of graphene has remained unexplored. Here we explore the use of CO₂ as a mild oxidant during the growth of graphene over Ni with CH₄ as the feedstock. Both our experimental and theoretical findings provide in-depth insight into the growth mechanisms and point to the mild oxidants playing multiple roles. Mild oxidants lead to the formation of a suboxide in the Ni, which suppresses the bulk diffusion of C species suggesting a surface growth mechanism. Moreover, the formation of a suboxide leads to enhanced catalytic activity at the substrate surface, which allows reduced synthesis temperatures, even as low as 700 °C. Even at these low temperatures, the quality of the graphene is exceedingly high as indicated by a negligible D mode in the Raman spectra. These findings suggest the use of mild oxidants in the CVD fabrication as a whole could have a positive impact