peri-Fused polyaromatic molecular contacts for perovskite solar cells.

Molecule-based selective contacts have become a crucial component to ensure high-efficiency inverted perovskite solar cells1-5. These molecules always consist of a conjugated core with heteroatom substitution to render the desirable carrier-transport capability6-9. So far, the design of successful conjugation cores has been limited to two N-substituted π-conjugated structures, carbazole and triphenylamine, with molecular optimization evolving around their derivatives2,5,10-12. However, further improvement of the device longevity has been hampered by the concomitant limitations of the molecular stability induced by such heteroatom-substituted structures13,14. A more robust molecular contact without sacrificing the electronic properties is in urgent demand, but remains a challenge. Here we report a peri-fused polyaromatic core structure without heteroatom substitution that yields superior carrier transport and selectivity over conventional heteroatom-substituted core structures. This core structure produced a relatively chemically inert and structurally rigid molecular contact, which considerably improved the performance of perovskite solar cells in terms of both efficiency and durability. The champion device showed an efficiency up to 26.1% with greatly improved longevity under different accelerated-ageing tests.

Oriented nucleation in formamidinium perovskite for photovoltaics.

The black phase of formamidinium lead iodide (FAPbI3) perovskite shows huge promise as an efficient photovoltaic, but it is not favoured energetically at room temperature, meaning that the undesirable yellow phases are always present alongside it during crystallization1-4. This problem has made it difficult to formulate the fast crystallization process of perovskite and develop guidelines governing the formation of black-phase FAPbI3 (refs. 5,6). Here we use in situ monitoring of the perovskite crystallization process to report an oriented nucleation mechanism that can help to avoid the presence of undesirable phases and improve the performance of photovoltaic devices in different film-processing scenarios. The resulting device has a demonstrated power-conversion efficiency of 25.4% (certified 25.0%) and the module, which has an area of 27.83 cm2, has achieved an impressive certified aperture efficiency of 21.4%.

Benchmarking the Match of Porous Carbon Substrate Pore Volume on Silicon Anode Materials for Lithium-Ion Batteries.

Silicon (Si) is one of the most promising anode materials for high-energy-density lithium-ion batteries. However, the huge volume expansion hinders its commercial application. Embedding amorphous Si nanoparticles in a porous carbon framework is an effective way to alleviate Si volume expansion, with the pore volume of the carbon substrates playing a pivotal role. This work demonstrates the impact of pore volume on the electrochemical performance of the silicon/carbon porous composites from two perspectives: 1) pore volume affects the loadings of Si particles; 2) pore volume affects the structural stability and mechanical properties. The smaller pore volume of the carbon substrate cannot support the high Si loadings, which results in forming a thick Si shell on the surface, thereby being detrimental to cycling stability and the diffusion of electrons and ions. On top of that, the carbon substrate with a larger pore volume has poor structural stability due to its fragility, which is also not conducive to realizing long cycle life and high rate performance. Achieving excellent electrochemical performances should match the proper pore volume with Si content. This study will provide important insights into the rational design of the silicon/carbon porous composites based on the pore volume of the carbon substrates.

HCOO- Doping-Induced Multiexciton Emissions in Cs3Cu2I5 Crystals for Efficient X-Ray Scintillation.

Self-trapped exciton (STE) luminescence, typically associated with structural deformation of excited states, has attracted significant attention in metal halide materials recently. However, the mechanism of multiexciton STE emissions in certain metal halide crystals remains largely unexplored. This study investigates dual luminescence emissions in HCOO- doped Cs3Cu2I5 single crystals using transient and steady-state spectroscopy. The dual emissions are attributed to intrinsic STE luminescence originating from the host lattice and extrinsic STE luminescence induced by external dopants, respectively, each of which can be triggered independently at distinct energy levels. Theoretical calculations reveal that multiexciton emission originates from structural distortion of the host and dopant STEs within the 0D lattice in their respective excited states. By meticulously tuning the excitation wavelength and selectively exciting different STEs, the dynamic alteration of color change in Cs3Cu2I5:HCOO- crystals is demonstrated. Ultimately, owing to an extraordinarily high photoluminescence quantum yield (99.01%) and a diminished degree of self-absorption in Cs3Cu2I5:HCOO- crystals, they exhibit remarkable X-ray scintillation characteristics with light yield being improved by 5.4 times as compared to that of pristine Cs3Cu2I5 crystals, opening up exciting avenues for achieving low-dose X-ray detection and imaging.

Sequencing-Dependent Impact of Carbon Coating on Microstructure Evolution and Electrochemical Performance of Pre-lithiated SiO Anodes: Enhanced Efficiency and Stability via Pre-Coating Strategy.

Silicon monoxide (SiO) has attracted considerable interest as anode material for lithium-ion batteries (LIBs). However, their poor initial Coulombic efficiency (ICE) and conductivity limit large-scale applications. Prelithiation and carbon-coating are common and effective strategies in industry for enhancing the electrochemical performance of SiO. However, the involved heat-treatment processes inevitably lead to coarsening of active silicon phases, posing a significant challenge in industrial applications. Herein, the differences in microstructures and electrochemical performances between prelithiated SiO with a pre-coated carbon layer (SiO@C@PLi) and SiO subjected to carbon-coating after prelithiation (SiO@PLi@C) are investigated. A preliminary carbon layer on the surface of SiO before prelithiation is found that can suppress active Si phase coarsening effectively and regulate the post-prelithiation phase content. The strategic optimization of the sequence where prelithiation and carbon-coating processes of SiO exert a critical influence on its regulation of microstructure and electrochemical performances. As a result, SiO@C@PLi exhibits a higher ICE of 88.0%, better cycling performance and lower electrode expansion than SiO@PLi@C. The pouch-type full-cell tests demonstrate that SiO@C@PLi/Graphite||NCM811 delivers a superior capacity retention of 91% after 500 cycles. This work provides invaluable insights into industrial productions of SiO anodes through optimizing the microstructure of SiO in prelithiation and carbon-coating processes.

Self-power, multiwavelength photodetector based on a Sn-doped Ge quantum dots/hexagonal silicon nanowire heterostructure.

Tin-doped germanium quantum dots (Sn-doped Ge QDs)-decorated hexagonal silicon nanowires (h-Si NWs) were adopted to overcome the low infrared response of silicon and the excess dark current of germanium. High-quality Sn-doped Ge QDs with a narrow bandgap can be achieved through Ge-Sn co-sputtering on silicon nanowires by reducing the contact area between heterojunction materials and Sn-induced germanium crystallization. The absorption limit of the heterostructure is extended to 2.2 µm, and it is sensitive to 375-1550 nm light at 0 V, which has optimality at 1342 nm, with a photo-to-dark current ratio of over 815, a responsivity of 0.154 A/W, and a response time of 0.93 ms. The superior performance of the Sn-doped Ge QDs/h-Si NW photodetector in multiwavelength is attractive for multi-scenario applications.

Nanosecond laser annealing processed surface-structured hyperdoped silicon for efficient near-infrared detection.

Surface-structured engineering of hyperdoped silicon can effectively facilitate the absorption of sub-bandgap photons in pristine single-crystal silicon (sc-Si). Here, we conducted different annealing approaches of ordinary thermal annealing (OTA) and nanosecond laser annealing (NLA) on modification of titanium-hyperdoped silicon (Si:Ti) surface structure, to achieve efficient near-infrared detection. It is presented that both OTA and NLA processes can improve the crystallinity of Si:Ti samples. In detail, atomic-resolved STEM characterization illustrates that NLA treatment will further eliminate the amorphous phase on Si:Ti surface to varying degrees. While one-dimensional periodic stacking fault structure of 9R-Si phase is formed at the surface of sc-Si and embedded in the Si matrix during the OTA process, which reveals the seamless interface of 9R-Si/sc-Si along with [11¯0] direction. Due to the high sub-bandgap light absorption and good crystal structure, the Si:Ti photodetector after NLA treatment with an energy density of 2.6 J cm-2exhibited the highest responsivity, reaching 151 mA W-1at 1550 nm even at a low operating voltage of 1 V. We assume the performance enhancement of NLA processed Si:Ti photodetectors can be attributed to two aspects, the one is NLA can reduce the recombination of photo-generated charge carriers in amorphous surface layer by improving crystallization, and the other is that NLA process can weaken the diffusion of titanium impurities due to the extremely rapid heating and cooling rates. This study presents prospects towards surface-structured silicon in infrared light detection.

Silicon-Nanomembrane-Based Broadband Synaptic Phototransistors for Neuromorphic Vision.

Neuromorphic vision has been attracting much attention due to its advantages over conventional machine vision (e.g., lower data redundancy and lower power consumption). Here we develop synaptic phototransistors based on the silicon nanomembrane (Si NM), which are coupled with lead sulfide quantum dots (PbS QDs) and poly(3-hexylthiophene) (P3HT) to form a heterostructure with distinct photogating. Synaptic phototransistors with optical stimulation have outstanding synaptic functionalities ranging from ultraviolet (UV) to near-infrared (NIR). The broadband synaptic functionalities enable an array of synaptic phototransistors to achieve the perception of brightness and color. In addition, an array of synaptic phototransistors is capable of simultaneous sensing, processing, and memory, which well mimics human vision.

Dielectric Regulation for Efficient Top-Emission Perovskite Light-Emitting Diodes with Suppressed Efficiency Roll-off.

Perovskite light-emitting diodes (PeLEDs) have shown incalculable application potential in the fields of next-generation displays and light communication owing to the rapidly increased external quantum efficiencies (EQEs). However, most PeLEDs obtain a maximum EQE at small current density (J) region and suffer from severe efficiency roll-off in different extents. Herein, it is demonstrated that the dopant with large dipole moment like KBF4 facilitates the effective dielectric regulation of perovskite emissive layer. The increased dielectric constant lowers the exciton binding energy and suppresses the Auger recombination of the 2D/3D segregated perovskite structure, which improves the photoluminescence quantum yield remarkably at an excitation intensity up to 103  mW cm-2 . Accordingly, the top-emission PeLED that delivers a high maximum EQE above 20% is fabricated and can retain EQE > 10% at an extremely high J of 708 mA cm-2 . These results represent one of the most efficient top-emission PeLEDs with ultra-low efficiency roll-off, which provide a viable methodology for tuning the dielectric response of perovskite films for improved high radiance performance of perovskite electroluminescence devices.

Two-dimensional devices and integration towards the silicon lines.

Despite technical efforts and upgrades, advances in complementary metal-oxide-semiconductor circuits have become unsustainable in the face of inherent silicon limits. New materials are being sought to compensate for silicon deficiencies, and two-dimensional materials are considered promising candidates due to their atomically thin structures and exotic physical properties. However, a potentially applicable method for incorporating two-dimensional materials into silicon platforms remains to be illustrated. Here we try to bridge two-dimensional materials and silicon technology, from integrated devices to monolithic 'on-silicon' (silicon as the substrate) and 'with-silicon' (silicon as a functional component) circuits, and discuss the corresponding requirements for material synthesis, device design and circuitry integration. Finally, we summarize the role played by two-dimensional materials in the silicon-dominated semiconductor industry and suggest the way forward, as well as the technologies that are expected to become mainstream in the near future.

Direct growth of graphene on hyper-doped silicon to enhance carrier transport for infrared photodetection.

The importance of infrared photodetectors cannot be overstated, especially in fields such as security, communication, and military. While silicon-based infrared photodetectors are widely used due to the maturity of the semiconductor industry, their band gap of 1.12 eV limits their infrared light absorption above 1100 nm, making them less effective. To overcome this limitation, we report a novel infrared photodetector prepared by growing graphene on the surface of zinc hyper-doped silicon. This technique utilizes hyper-doping to introduce deep level assisted infrared light absorption benefit from the enhanced carrier collection capacity of graphene. Without introducing new energy consumption, the hyper-doped substrate annealing treatment is completed during the growth of graphene. By the improvement of transport and collection of charge carriers, the graphene growth adjusts the band structure to upgrade electrode contact, resulting in a response of 1.6 mA W-1under laser irradiation with a wavelength of 1550 nm and a power of 2 mW. In comparison, the response of the photodetector without graphene was only 0.51 mA W-1, indicating a three-fold performance improvement. Additionally, the device has lower dark current and lower noise current, resulting in a noise equivalent power of 7.6 × 10-8W Hz-0.5. Thus, the combination of transition metal hyper-doping and graphene growth technology has enormous potential for developing the next generation of infrared photodetectors.

Molecular beam epitaxy growth and scanning tunneling microscopy study of 2D layered materials on epitaxial graphene/silicon carbide.

Since the advent of atomically flat graphene, two-dimensional (2D) layered materials have gained extensive interest due to their unique properties. The 2D layered materials prepared on epitaxial graphene/silicon carbide (EG/SiC) surface by molecular beam epitaxy (MBE) have high quality, which can be directly applied without further transfer to other substrates. Scanning tunneling microscopy and spectroscopy (STM/STS) with high spatial resolution and high-energy resolution are often used to study the morphologies and electronic structures of 2D layered materials. In this review, recent progress in the preparation of various 2D layered materials that are either monoelemental or transition metal dichalcogenides on EG/SiC surface by MBE and their STM/STS investigations are introduced.

High-Performance and Self-Powered X-Ray Detectors Made of Smooth Perovskite Microcrystalline Films with 100†µm Grains.

Perovskite single crystals and polycrystalline films have complementary merits and deficiencies in X-ray detection and imaging. Herein, we report preparation of dense and smooth perovskite microcrystalline films with both merits of single crystals and polycrystalline films through polycrystal-induced growth and hot-pressing treatment (HPT). Utilizing polycrystalline films as seeds, multi-inch-sized microcrystalline films can be in situ grown on diverse substrates with maximum grain size reaching 100 µm, which endows the microcrystalline films with comparable carrier mobility-lifetime (µτ) product as single crystals. As a result, self-powered X-ray detectors with impressive sensitivity of 6.1×104  µC Gyair -1 cm-2 and low detection limit of 1.5 nGyair s-1 are achieved, leading to high-contrast X-ray imaging at an ultra-low dose rate of 67 nGyair s-1 . Combining with the fast response speed (186 µs), this work may contribute to the development of perovskite-based low-dose X-ray imaging.

Phase-Stable Wide-Bandgap Perovskites for Four-Terminal Perovskite/Silicon Tandem Solar Cells with Over 30% Efficiency.

Wide-bandgap perovskite solar cells (PSCs) with an optimal bandgap between 1.7 and 1.8 eV are critical to realize highly efficient and cost-competitive silicon tandem solar cells (TSCs). However, such wide-bandgap PSCs easily suffer from phase segregation, leading to performance degradation under operation. Here, it is evident that ammonium diethyldithiocarbamate (ADDC) can reduce the detrimental I2 back to I- in precursor solution, thereby reducing the density of deep level traps in perovskite films. The resultant perovskite film exhibits great phase stability under continuous illumination and 30-60% relative humidity conditions. Due to the suppression of defect proliferation and ion migration, the PSCs deliver great operation stability which retain over 90% of the initial power conversion efficiency (PCE) after 500 h maximum power point tracking. Finally, a highly efficient semitransparent PSC with a tailored bandgap of 1.77 eV, achieving a PCE approaching 18.6% with a groundbreaking open-circuit voltage (VOC ) of 1.24 V enabled by ADDC additive in perovskite films is demonstrated. Integrated with a bottom silicon solar cell, a four-terminal (4T) TSC with a PCE of 30.24% is achieved, which is one of the highest efficiencies in 4T perovskite/silicon TSCs.

Vacuum-Vapor-Deposited 0D/3D All-Inorganic Perovskite Composite Films toward Low-Threshold Amplified Spontaneous Emission and Lasing.

Vacuum vapor deposition (VVD) is a promising way to advancing the commercialization of perovskite light sources owing to its convenience for wafer-scale mass production and compatibility with silicon photonics manufacturing infrastructure. However, the light emission performance of VVD-grown perovskites still lags far behind that of the conventional solution-processed counterparts due to their inferior luminescence properties. Here, a 0D/3D cesium-lead-bromide perovskite composite film is prepared on Si/SiO2 substrates through composition modulation with the VVD method, which exhibits an ultralow amplified spontaneous emission (ASE) threshold down to 14.3 µJ cm-2 in the optimal films, which is on par with that of the solution-processed counterparts. Meanwhile, they also display intriguing operational stability with negligible emission intensity decay under continuous excitation above ASE threshold for 4 h in the air. The outstanding ASE performance mainly originates from the reduced trap density and weakened electron-phonon coupling in the 3D CsPbBr3 phase enabled by the incorporation of the 0D Cs4 PbBr6 phase. Finally, by integrating the composite film with the distributed feedback (DFB) cavity, DFB lasing is achieved with a low threshold of 18.2 µJ cm-2 under nanosecond-pulsed laser pumping, which highlights the potential of VVD-processed perovskites for developing high-performance lasers.

High detectivity graphene/si heterostructure photodetector with a single hydrogenated graphene atomic interlayer for passivation and carrier tunneling.

Hydrogenated graphene is easy to prepare and chemically stable. Besides, hydrogenation of graphene can open the band gap, which is vital for electronic and optoelectronic applications. Graphene/Si photodetector (PD) has been widely studied in imaging, telecommunications, and other fields. The direct contact between graphene and Si can form a Schottky junction. However, it suffers from poor interface state, where the carrier recombination at the interface causes serious leakage current, which in turn leads to a decrease in the detectivity. Hence, in this study, hydrogenated graphene is used as an interfacial layer, which passivates the interface of graphene/Si (Gr/Si) heterostructure. Besides, the single atomic layer thickness of hydrogenated graphene is also crucial for the tunneling transport of charge carriers and its suitable energy band position reduces the recombination of carrier. The fabricated graphene/hydrogenated-graphene/Si (Gr/H-Gr/Si) heterostructure PD showed an extremely low dark current about 10-7A. As a result, it had low noise current and exhibited a high specific detectivity of âˆ¼2.3 × 1011Jones at 0 V bias with 532 nm laser illumination. Moreover, the responsivity of the fabricated PD was found to be 0.245 A W-1at 532 nm illumination with 10µW power. These promising results show a great potential of hydrogenated graphene to be used as an interface passivation and carrier tunneling layer for the fabrication of high-performance Gr/Si heterostructure PDs.

Polyoxometalate Interlayered Zinc-Metallophthalocyanine Molecular Layer Sandwich as Photocoupled Electrocatalytic CO2 Reduction Catalyst.

Developing efficient and robust heterogeneous metallophthalocyanine electrocatalysts for CO2 reduction remains a challenge. Here, a general synthetic method of zinc-metallophthalocyanine (MPc) molecular layer/polyoxometalate (POM) sandwich lamellar material is developed, and thus improved performance of electrocatalytic and photocoupled electrocatalytic CO2 reduction is achieved. The incorporation of POM could prevent the packing of MPc molecular layers from aggregation, which would be favorable to the exposure of active sites. The molecular layer sandwich catalyst presents superior CO2 reduction activity, delivering the highest CO Faradaic efficiency (FECO) of 96.1% at -0.7 V vs RHE in dark field. Under light irradiation, over 93% FECO is achieved in a broad potential range from -0.6 to -0.9 V vs RHE with a maximum of 96.2%, and the carbon monoxide turnover frequency could exceed 2060 h-1. Photoelectrochemical tests and luminescence characterizations reveal the molecular layer is beneficial for carrier separation during light irradiation; density functional theory calculations and electron paramagnetic resonance indicated a 2-fold enhancement of the external light field on the catalytic performance.

Recent Progress on the Scanning Tunneling Microscopy and Spectroscopy Study of Semiconductor Heterojunctions.

The band alignment, interface states, interface coupling, and carrier transport of semiconductor heterojunctions (SHs) need to be well understood for the design and fabrication of various important semiconductor structures and devices. Scanning tunneling microscopy (STM) with high spatial resolution and scanning tunneling spectroscopy (STS) with high energy resolution are significantly contributing to the understanding on the important properties of SHs. In this work, the recent progress on the use of STM and STS to study lateral, vertical and bulk SHs is reviewed. The spatial structures of SHs with atomically flat surface have been examined with STM. The electronic band structures (e. g., the band offset, interface state, and space charge region) of SHs are measured with STS. Combined with the spatial structures and the tunneling spectra features, the mechanism for the carrier transport in the SH may be proposed.

Au-Polyoxometalates A-B-A-B Type Copolymer-Analogue Sub-1 nm Nanowires.

Here it is shown that polyoxometalate (POM) clusters (H3 PW12 O40 ·xH2 O, PW12 ) can be introduced to interact with Au nanoclusters to form the "A-B-A-B" type building block ("A" represents Au nanoclusters and "B" stands for PW12 clusters), which continue to grow into copolymer-analogue Au-PW12 sub-1 nm nanowires. Due to the synergetic effect of Au nanoclusters and POMs, the obtained Au-PW12 sub-1 nm nanowires efficiently perform catalytic activity in the photo-electrochemical converting CO2 into CO. Under light, the catalyst maintains remarkable faradic efficiency (FE) of ≈99% from -0.7 to -0.9V (RHE), which is better than that in dark (FE of 66.4-90.64% from -0.7 to -0.9 V (RHE)). Density functional theory calculations and cryo-electron microscope images support the "A-B-A-B" type of structure and mechanistic studies also reveal the higher reactivity toward COOH* formation and CO adsorption on the catalyst, which lead to the superior catalytic activity in CO2 reduction reaction.

CO2 Footprint of Thermal Versus Photothermal CO2 Catalysis.

Transformation of CO2 into value-added products via photothermal catalysis has become an increasingly popular route to help ameliorate the energy and environmental crisis derived from the continuing use of fossil fuels, as it can integrate light into well-established thermocatalysis processes. The question however remains whether negative CO2 emission could be achieved through photothermal catalytic reactions performed in facilities driven by electricity mainly derived from fossil energy. Herein, we propose universal equations that describe net CO2 emissions generated from operating thermocatalysis and photothermal reverse water-gas shift (RWGS) and Sabatier processes for batch and flow reactors. With these reactions as archetype model systems, the factors that will determine the final amount of effluent CO2 can be determined. The results of this study could provide useful guidelines for the future development of photothermal catalytic systems for CO2 reduction.