Semiconductors are a major category of functional materials essential to various applications to sustain the modern society. Most applied materials or devices utilizing semiconductors are enabled by ...interfaces or junctions, such as solar cells, electronic/photonic devices, environmental sensors, and redox hetero‐catalysts. Herein, the author provides a critical commentary on photoemission measurement of the work function and, more importantly, the electron affinity of semiconductors essential for energy band diagram of heterojunctions. Particular effort is made towards addressing complications associated with Fermi level pinning due to surficial states of doped semiconductors.
UPS measurement of work functions and band edge levels of semiconductors, with particular focus on addressing complication due to Fermi level pinning.
Porous carbon materials have demonstrated exceptional performance in a variety of energy‐ and environment‐related applications. Over the past decades, tremendous efforts have been made in the ...coordinated design and fabrication of porous carbon nanoarchitectures in terms of pore sizes, surface chemistry, and structure. Herein, structure‐oriented carbon design and applications are reviewed. The unique properties of porous carbon materials that offer them promising design opportunities and broad applicability in some representative fields, including water remediation, CO2 capture, lithium‐ion batteries, lithium–sulfur batteries, lithium metal anodes, Na‐ion batteries, K‐ion batteries, supercapacitors, and the oxygen reduction reaction are highlighted. Then, the most up‐to‐date strategies for structural control and functionalization of porous carbons are summarized, toward tailoring microporous, mesoporous, macroporous, and hierarchically porous carbons with disordered or ordered, amorphous or graphitic structures. Meanwhile, the emerging features of these structures in various applications are introduced where applicable. Finally, insights into the challenges and perspectives for future development are provided.
Herein, the structure–property relationships of porous carbon materials in water remediation, carbon capture, lithium‐ion batteries, lithium–sulfur batteries, Li metal anodes, Na‐ion batteries, K‐ion batteries, supercapacitors, and oxygen reduction reactions are proposed. The recent progress in structural control and functionalization of porous carbons are also summarized, in terms of achieving microporous, mesoporous, macroporous, and hierarchically porous carbons.
Three‐dimensional (3D) metal‐halide perovskite solar cells (PSCs) have demonstrated exceptional high efficiency. However, instability of the 3D perovskite is the main challenge for industrialization. ...Incorporation of some long organic cations into perovskite crystal to terminate the lattice, and function as moisture and oxygen passivation layer and ion migration blocking layer, is proven to be an effective method to enhance the perovskite stability. Unfortunately, this method typically sacrifices charge‐carrier extraction efficiency of the perovskites. Even in 2D–3D vertically aligned heterostructures, a spread of bandgaps in the 2D due to varying degrees of quantum confinement also results in charge‐carrier localization and carrier mobility reduction. A trade‐off between the power conversion efficiency and stability is made. Here, by introducing 2D C6H18N2O2PbI4 (EDBEPbI4) microcrystals into the precursor solution, the grain boundaries of the deposited 3D perovskite film are vertically passivated with phase pure 2D perovskite. The phases pure (inorganic layer number n = 1) 2D perovskite can minimize photogenerated charge‐carrier localization in the low‐dimensional perovskite. The dominant vertical alignment does not affect charge‐carrier extraction. Therefore, high‐efficiency (21.06%) and ultrastable (retain 90% of the initial efficiency after 3000 h in air) planar PSCs are demonstrated with these 2D–3D mixtures.
High‐efficiency (21.06%) and durable 2D–3D vertical aligned perovskite solar cells (PSCs) with phase pure 2D perovskite are demonstrated. The phase pure 2D perovskite minimizes photo‐generated charge‐carrier localization in the low‐dimensional perovskite; the dominant vertical alignment does not affect charge‐carrier extraction. The traditional constraint of trade‐off between efficiency and stability in PSC is overcome.
Using a materials genome approach on the basis of density functional theory, we have formulated a new class of inorganic electrolytes for the fast diffusion of Li
+
ions by fine-tuning the lattice ...chemistry of anti-perovskite structures. Systematic modelling was carried out to determine the structural stability and ion transport characteristics in Li
3
AX-based cubic anti-perovskites by alloying on the chalcogen lattice site (A) and alternative occupancy of the halogen site (X). In addition to identifying effective ways of reducing diffusion barriers for Li
+
ions in anti-perovskite phases
via
the suitable designation of lattice occupancy, the current theoretical study has led to the discovery and synthesis of a new phase with a double-anti-perovskite structure, Li
6
OSI
2
(or Li
3
O
0.5
S
0.5
I). This new compound has a fairly low activation barrier for Li
+
diffusion, together with a wide energy band gap to hinder the conduction of electrons.
Understanding the fundamental properties of buried interfaces in perovskite photovoltaics is of paramount importance to the enhancement of device efficiency and stability. Nevertheless, accessing ...buried interfaces poses a sizeable challenge because of their non‐exposed feature. Herein, the mystery of the buried interface in full device stacks is deciphered by combining advanced in situ spectroscopy techniques with a facile lift‐off strategy. By establishing the microstructure–property relations, the basic losses at the contact interfaces are systematically presented, and it is found that the buried interface losses induced by both the sub‐microscale extended imperfections and lead‐halide inhomogeneities are major roadblocks toward improvement of device performance. The losses can be considerably mitigated by the use of a passivation‐molecule‐assisted microstructural reconstruction, which unlocks the full potential for improving device performance. The findings open a new avenue to understanding performance losses and thus the design of new passivation strategies to remove imperfections at the top surfaces and buried interfaces of perovskite photovoltaics, resulting in substantial enhancement in device performance.
The mystery of the buried interface in perovskite photovoltaics is deciphered by combining advanced spectroscopy techniques with a lift‐off strategy. The findings open a new avenue to understanding performance losses and thus the design of unique passivation strategies to remove imperfections at the top surfaces and buried interfaces of perovskite photovoltaics, resulting in substantial enhancement in device performance.
Li-S batteries are considered as a highly promising candidate for the next-generation energy storage system, attributing to their tremendous energy density. However, the two-dimensional island ...nucleation-growth process of lithium sulfide leads to a thick insulating film covering the electrode, inducing slow electrons transfer and mass-transfer of ions and liquid sulfur species in working Li-S cells. Here, we demonstrate a bio-inspired strategy of constructing ant-nest-like hierarchical porous ultrathin carbon nanosheet networks with the implants of metallic nanoparticles electrocatalysts (HPC-MEC) as efficient nanoreactors enabling rapid mass transfer, via a simple and green NaCl template. Such nanoreactors with a large active surface area could effectively anchor polysulfides for mitigating the shuttle effect, facilitating uniformly thin Li
2
S film, and promoting the mass transfer for fast sulfur species conversions. This helps contribute to a continuously high sulfur utilization in Li-S batteries with the HPC-MEC reactors. As a typical exhibition, cobalt embedded hierarchical porous carbon (HPC-Co) could realize to deliver a remarkably high specific capacity of 1,540.6 mAh·g
−1
, an excellent rate performance of 878.8 mAh·g
−1
at 2 C, and high area capacity of 11.6 mAh·cm
−2
at a high sulfur load of 10 mg·cm
−2
and low electrolyte/sulfur ratio of 5 µL·mg
−1
.
Domain boundaries are regarded as the effective active sites for electrochemical energy storage materials due to defects enrichment therein. However, layered double hydroxides (LDHs) tend to grow ...into single crystalline nano sheets due to their unique two-dimentional (2D) lattice structure. Previously, much efforts were made on the designing hierarchical structure to provide more exposed electroactive sites as well as accelerate the mass transfer. Herein, we demonstrate a strategy to introduce low angle grain boundary (LAGB) in the flakes of Ni/Co layered double hydroxides (NiCo-LDHs). These defect-rich nano flakes were self-assembled into hydrangea-like spheres that further constructed hollow cage structure. Both the formation of hierarchical structure and grain boundaries are interpreted with the synergistic effect of Ni
2+
/Co
2+
ratio in an “etching-growth” process. The domain boundary defect also results in the preferential formation of oxygen vacancy (Vo). Additionally, density functional theory (DFT) calculation reveals that Co substitution is a critical factor for the formation of adjacent lattice defects, which contributes to the formation of domains boundary. The fabricated battery-type Faradaic NiCo-LDH-2 electrode material exhibits significantly enhanced specific capacitance of 899 C·g
−1
at a current density of 1 A·g
−1
. NiCo-LDH-2//AC asymmetric capacitor shows a maximum energy density of 101.1 Wh·kg
−1
at the power density of 1.5 kW·kg
−1
.
Even though ultra-fast Li+ ion conductors based on sulfides such as LGPS and Li6PS5Cl have been developed in recent years, rather limited advancement has been made towards developing all-solid-state ...lithium ion batteries due to serious interface-related problems. Here in this work, we have carried out extensive fundamental modelling to formulate a system of materials based on hali-chalcogenide Li6PA5Cl argyrodites (A is the site for chalcogen species), so that materials with chemically and structurally compatible characteristics can be used as both a superb electrolyte and excellent buffer coatings over electrode surfaces. All solid-state-batteries (ASSBs) in the form of Li|Li6PO4SCl|Li6PO5Cl|Li0.25MnO2 are thus recommended, so that buffer coatings based on O-rich hali-chalcogenides help avoid interfacial reactions, owing to their high stability with respect to the cathodes and greatly enhanced chemical potential with respect to Li/Li+. Such batteries fundamentally have high mechanical and electrochemical stability, thus enabling high performance and great endurance to operational voltage.
Lithium–sulfur (Li–S) batteries have been regarded as a promising next‐generation energy storage technology for their ultrahigh theoretical energy density compared with those of the traditional ...lithium‐ion batteries. However, the practical applications of Li–S batteries are still blocked by notorious problems such as the shuttle effect and the uncontrollable growth of lithium dendrites. Recently, the rapid development of electrospinning technology provides reliable methods in preparing flexible nanofibers materials and is widely applied to Li–S batteries serving as hosts, interlayers, and separators, which are considered as a promising strategy to achieve high energy density flexible Li–S batteries. In this review, a fundamental introduction of electrospinning technology and multifarious electrospinning‐based nanofibers used in flexible Li–S batteries are presented. More importantly, crucial parameters of specific capacity, electrolyte/sulfur (E/S) ratio, sulfur loading, and cathode tap density are emphasized based on the proposed mathematic model, in which the electrospinning‐based nanofibers are used as important components in Li–S batteries to achieve high gravimetric (WG) and volume (WV) energy density of 500 Wh kg−1 and 700 Wh L−1, respectively. These systematic summaries not only provide the principles in nanofiber‐based electrode design but also propose enlightening directions for the commercialized Li–S batteries with high WG and WV.
A mathematic model is proposed using the electrospinning‐based nanofibers serve as a cathode and anode host, and separator to achieve high gravimetric (WG) and volume (WV) energy density of 500 Wh kg−1 and 700 Wh L−1 in Li–S batteries, respectively, by emphasizing the crucial parameters of specific capacity, electrolyte/sulfur (E/S) ratio, sulfur loading, and cathode tap density in the cell.
Photoelectron transfer between heterojuctions is an important process for photocatalysis, and identification of the electron transfer process provides valuable information for catalyst design. ...Herein, Ti3C2, one of the widely used two‐dimensional materials, is used to produce a heterojunction of TiO2 and Ti3C2 by an in situ growth method and the photogenerated electrons transfer between the two components for photocatalytic water splitting to hydrogen is investigated. Theoretical simulation and experimental tests proclaim that electrons transfer from Ti3C2 to TiO2 forms an internal electric field, which implies that there exists the driving force of electronic movement from TiO2 to Ti3C2. In situ irradiation X‐ray photoelectron spectroscopy shows the binding energies of TiC (in Ti3C2) and TiO (in TiO2) move toward negative and positive positions, respectively, verifying the photogenerated electrons produced from TiO2 and transferring to Ti3C2 driven by the internal electric field. In addition, the amount of TiO2 nanoparticles also affects the hydrogen evolution rate. Several parallel experiments are designed to uncover the fact that less or excess amount of TiO2 nanoparticles leads to a tinier shift of binding energy, which hints the quantity of heterojunction is a considerable factor in photocatalytic performance. This work develops a new method to directly monitor the photoelectron transfer process between heterojuctions.
An in situ irradiation X‐ray photoelectron spectroscopy coupled with UV light optical fiber measurement setup is developed to monitor the photoelectron transfer process between heterojuctions.
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