Interface Dipole Research Articles

An Energy Level Alignment Study of 2PACz Molecule on Perovskite Device‐Related Interfaces by Vacuum Deposition

Self‐assembling molecules (SAM) have been widely used in inverted perovskite solar cells (PSC) as a hole transfer layer due to nearly lossless charge transfer giving excellent device performance. However, the energy level alignment between SAM‐ and PSC‐related interfaces has not been systematically studied. Herein, the 2PACz, a typical SAM with the largest dipole moment, is chosen as the model system and is studied by vacuum deposition. It is found that the energy level alignment is determined by the orientation of 2PACz molecules on a different substrate. The molecules are lying down on highly oriented pyrolytic graphite and giving nearly zero interface dipole. On solvent‐cleaned and plasma‐treated indium tin oxide (ITO) substrates, the SAM is vertically assembled with 0.22 and 0.13 eV work function increases, respectively. However, on sputtered ITO, SAM is assembled with upside down orientation, with 0.51 eV work function decrease. The change of orientation is due to strong interaction between oxygen vacancies in ITO substrate and carbazole head group of 2PACz. On perovskite film, SAM also shows a slightly upward orientation with additional passivation of free MA+ ions. Herein, it is confirmed that the energy level alignment of SAM plays an important role in hole extraction.

Dipole-induced transitions from Schottky to Ohmic contact at Janus MoSiGeN4/metal interfaces.

Janus MoSiGeN4 monolayers exhibit exceptional mechanical stability and high electron mobility, which make them a promising channel candidate for field-effect transistors (FETs). However, the high Schottky barrier at the contact interface would limit the carrier injection efficiency and degrade device performance. Herein, using density functional theory calculations and machine learning methods, we investigated the interfacial properties of the Janus MoSiGeN4 monolayer and metal electrode contacts. The results demonstrated that the n-type/p-type Schottky and n-type Ohmic contacts can be realized in metal/MoSiGeN4 by changing the built-in electric dipole orientation of MoSiGeN4. Specifically, the contact type of Cu/MoSiGeN4 (Au/MoSiGeN4) transfers from an n-type Schottky (p-type Schottky) contact to an n-type Ohmic (n-type Schottky) contact when the contact side of MoSiGeN4 switches from Si-N to Ge-N. In addition, the Fermi level pinning (FLP) effect of metal/MoSiGeN4 with the Si-N side is weaker than that of metal/MoSiGeN4 with the Ge-N side due to the effect of intrinsic dipole and interface dipole. Notably, a simplified mathematical expression ΔV/WM is developed to describe the Schottky barrier height at metal/MoSiGeN4 interfaces using the machine learning method. These findings offer valuable guidance for the design and development of high-performance Janus MoSiGeN4-based electronic devices.

Improving electron injection of organic light-emitting transistors via interface layer design.

Ambipolar transport is crucial for constructing high performance organic light-emitting transistors (OLETs), but the ambipolar feature is usually not exhibited due to ineffective electron injection especially in symmetric device geometry. Herein, we show that electron injection could be greatly enhanced through the judicious design of an organic interface layer of 3,7-di(2-naphthyl)dibenzothiophene S,S-dioxide (DNaDBSO) which shows an interfacial dipole effect upon contact with a metal electrode, especially an Au electrode. When incorporating a DNaDBSO film beneath Au electrodes, the electron injection and mobility were significantly enhanced in 2,6-diphenylanthracene-based OLETs, and thus ambipolar transport (μmaxh: 2.17 cm2 V-1 s-1, μmaxe: 0.053 cm2 V-1 s-1) was effortlessly obtained. Furthermore, the shift of the electroluminescent region was obviously observed upon modulation of gate voltage, which demonstrates efficient electron injection and intrinsic ambipolar transporting properties in devices. This study provides a new avenue for regulating the interface in electroluminescent devices towards high performance simple-structured OLETs in applications.

The investigation of main electrical parameters, energy dependent profiles of surface states and their lifetimes in the Au/n-Si Schottky diodes with (PVA-Fe3O4) interlayer depend on frequency and voltage

Abstract In this article, the impedance-voltage-frequency (Z-V-f) measurements of the fabricated Au/(PVA-Fe3O4)/n-Si SDs have been performed between 0.1 kHz and 1 MHz, and in the ±3 V range. Main important electronic parameters of the Schottky diode (SD) like diffusion - potential (VD), Fermi - energy (EF), barrier - height (ΦB), depletion layer (WD), and max. electric field (Em) were extracted from the reverse bias 1/C2 - V plots in a wide frequency range. The voltage-reliant variations of the surface states (Nss) have been calculated by using low—high frequency capacitance (CLF-CHF), and parallel conductance or admittance models and compared to each other. The voltage-reliant resistance profile of Ri has also been obtained from the Nicollian & Brews method for all frequencies. All these results indicate that these main electrical parameters are strongly dependent on voltage and frequency due to the existence of Nss, their lifetimes (τ), interfacial organic layer, Rs, interface, and dipole polarizations. But, while Nss is effective, both in depletion and inversion regions, Rs is dominant at the strong-accumulation region at high enough frequency.

Interfacial Field-Effect Enabling High-Performance Perovskite Photovoltaics.

Currently, the power conversion efficiency (PCE) of inverted perovskite solar cells (PSCs) is still limited by reduced open-circuit voltage (VOC), due to defect-induced charge recombination. Most studies focus on defect passivation and improving carrier transport through introducing passivating molecules or macroscopic physical fields. Herein, to mitigate energy level mismatch and recombination losses induced by interface defects, an interface electric-field passivation is introduced, employing the ordered arrangement of the dipole molecule benzenesulfonyl chloride (BC). An enhanced VOC is achieved without the introduction of an external physical field, owing to the interfacial dipole field effect and chemical passivation by BC. Subsequently, an inverted device with a PCE of 25.41% is obtained, alongside exceptional stability, retaining 95% of the initial efficiency after 1157 h. This work demonstrates the effective dipole-induced interfacial field-effect passivation in inverted PSCs and contributes to further advancements in the efficiency and stability of inverted devices.

Interfacial chemistry at solid-liquid van der Waals heterojunctions enabling sub-5 nm Ohmic contacts for monolayer semiconductors.

The decoupling of electronic states between metals and semiconductors through controlled construction of artificial van der Waals (vdW) heterojunctions enables tailored Schottky barriers. However, the interfacial chemistry, especially involving solid-liquid interfaces, remains unexplored. Here, first principles calculations reveal unexpected strong Fermi-level pinning in various metal/MoS2 vdW heterojunctions with intercalated ice-like water bilayers. The polarization orientation of water in contact with metals of different work functions varies significantly, while the effective work function of the metals consistently decreases. Aluminum and scandium exhibit significant interfacial dipoles associated with hydrogen-bonding interactions when contacting MoS2 with intercalated water, leading to heavily doped n-type Ohmic contacts. The contact length of a monolayer MoS2 transistor with aluminum/intercalated-water (or hydroxyl) contacts can be scaled down to sub-5 nm due to a significant reduction in contact resistance, facilitated by strong interfacial charge transfer and hydrogen-bonding-enhanced resonant tunneling effects. This demonstrates a promising approach to regulating the contact properties via interfacial chemistry.

Atomic level insight into the variation and tunability of band alignment between Si and amorphous SiO2/HfO2

Abstract The band alignment between silicon and high-k dielectric, which is a key factor to device operation and device reliability, is still suffering from uncontrolled fluctuation and ambiguous understanding. Here by conducting atomic level ab initio calculations on realistic Si/SiO2/HfO2 stacks, we manage to reveal the physical origin of band alignment fluctuations, i.e. oxygen density dependent interface and surface dipoles, and demonstrate that the band offsets can be tuned without introducing other materials. This is instructive to reduce gate tunneling current, alleviate device-to-device variation, and tune threshold voltage. Besides, this study indicates that great attention should be paid to model construction in the emerging atomistic study of semiconductor devices.

Dipole Modulation Engineering Enhances Structural Order of PEDOT:PSS for Efficient and Stable InP-Based QLEDs.

Indium phosphide (InP)-based quantum dot light-emitting diodes (QLEDs) are promising for future lighting and display applications due to their high color purity and brightness. However, their efficiency and stability are often limited by the disordered structure of the widely used poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS), which impairs charge transport. Herein, we present a strategy to enhance the performance of InP-based QLEDs by modifying PEDOT:PSS through interfacial dipole modulation using molybdenum oxide (MoOx) nanoparticles. The strong hydrogen bonding between MoOx and PSS creates strong dipole-dipole interactions, reducing the separation of PEDOT-rich regions, enhancing π-π stacking and conductivity. This optimization facilitates balanced electron and hole injection, increasing external quantum efficiency (EQE) from 12.2% in control devices to 17.8% in the treated devices, along with a brightness enhancement from 32,998 to 43,567 cd m-2. Notably, our treated devices exhibit a reduction in efficiency attenuation compared to other reported InP-based QLEDs, particularly at high brightness levels of 5000 and 10,000 cd m-2, with EQE attenuation of only 4 and 9%, respectively, compared to 16 and 30% for controls. This work highlights the potential of dipole engineering in advancing InP-based QLED technology, providing a pathway for developing high-performance, stable, and eco-friendly lighting and displays.

3,6-Bis(methylthio)-9H-carbazole Based Self-Assembled Monolayer for Highly Efficient and Stable Inverted Perovskite Solar Cells.

The photovoltaic performance of inverted perovskite solar cells (PSCs) relies on effectively managing the interface between the hole extraction layer and the light-absorbing perovskite layer. In this study, we have synthesised (4-(3,6-bis(methylthio)-9H-carbazol-9-yl)butyl)phosphonic acid (MeS-4PACz), which forms a self-assembled monolayer on the fluorine-doped tin oxide (FTO) electrode. The molecule's methylthio substituents generate a favourable interfacial dipole moment and interact with the perovskite layer. This interaction results in well-aligned energy levels among the FTO/SAM/perovskite layers, promoting efficient hole extraction and significantly reducing carrier recombination losses. Additionally, the methylthio groups passivate iodide vacancies and interact with Pb2+ ions of the perovskite, reducing defect-induced trap states and enhancing the crystalline growth of the perovskite layer. Consequently, inverted PSCs incorporating MeS-4PACz achieve a remarkable power conversion efficiency of 25.13%, along with outstanding photostability.

3,6‐Bis(methylthio)‐9H‐carbazole Based Self‐Assembled Monolayer for Highly Efficient and Stable Inverted Perovskite Solar Cells

The photovoltaic performance of inverted perovskite solar cells (PSCs) relies on effectively managing the interface between the hole extraction layer and the light‐absorbing perovskite layer. In this study, we have synthesised (4‐(3,6‐bis(methylthio)‐9H‐carbazol‐9‐yl)butyl)phosphonic acid (MeS‐4PACz), which forms a self‐assembled monolayer on the fluorine‐doped tin oxide (FTO) electrode. The molecule's methylthio substituents generate a favourable interfacial dipole moment and interact with the perovskite layer. This interaction results in well‐aligned energy levels among the FTO/SAM/perovskite layers, promoting efficient hole extraction and significantly reducing carrier recombination losses. Additionally, the methylthio groups passivate iodide vacancies and interact with Pb2+ ions of the perovskite, reducing defect‐induced trap states and enhancing the crystalline growth of the perovskite layer. Consequently, inverted PSCs incorporating MeS‐4PACz achieve a remarkable power conversion efficiency of 25.13%, along with outstanding photostability.

Buried hole-selective interface engineering for high-efficiency tin-lead perovskite solar cells with enhanced interfacial chemical stability

Mixed Sn-Pb perovskites are attracting significant attention due to their narrow bandgap and consequent potential for all-perovskite tandem solar cells. However, the conventional hole transport materials can lead to band misalignment or induce degradation at the buried interface of perovskite. Here we designed a self-assembled material 4-(9H-carbozol-9-yl)phenylboronic acid (4PBA) for the surface modification of the substrate as the hole-selective contact. It incorporates an electron-rich carbazole group and conjugated phenyl group, which contribute to a substantial interfacial dipole moment and tune the substrate’s energy levels for better alignment with the Sn-Pb perovskite energy levels, thereby promoting hole extraction. Meanwhile, enhanced perovskite crystallization and improved contact at bottom of the perovskite minimized defects within perovskite bulk and at the buried interface, suppressing non-radiative recombination. Consequently, Sn-Pb perovskite solar cells using 4PBA achieved efficiencies of up to 23.45%. Remarkably, 4PBA layer provided superior interfacial chemical stability, and effectively mitigated device degradation. Unencapsulated devices retained 93.5% of their initial efficiency after 2000 h of shelf storage.

The influence of water polarization on slip friction at charged interfaces.

The present study employs equilibrium molecular dynamics simulations to explore the potential mechanism for controlling friction by applying electrostatic fields in nanoconfined aqueous electrolytes. The slip friction coefficient demonstrates a gradual increase corresponding to the surface charge density for pure water and aqueous electrolytes, exhibiting a similar trend across both nanochannel walls. An expression is formulated to rationalize the observed slip friction behavior, describing the effect of the electric field on the slip friction coefficient. According to this formulation, the slip friction coefficient increases proportionally to the square of the uniform electric field emanating from the charged electrode. This increase in slip friction results from the energy change due to the orientation polarization of interfacial water dipoles. The minimal variations in the empirically determined proportionality constant for pure water and aqueous electrolytes indicate that water polarization primarily governs slip friction at charged interfaces. These findings offer insights into the electrical effects on nanoscale lubrication of aqueous electrolytes, highlighting the significant role of water polarization in determining slip.

Doping-free Janus homojunction solar cell with efficiency exceeding 23%

Photovoltaic solar cell is one of the main renewable energy sources, and its power conversion efficiency (PCE) is improved by employing doping or heterojunction to reduce the photogenerated carrier recombination. Here, we propose a straightforward strategy for constructing high-PCE homojunction solar cells, where intrinsic driving forces can simultaneously enhance the efficiency of carrier separation and transport. Thanks to the intrinsic dipole of Janus structure, doping-free Janus homojunction has naturally not only a type-II band alignment to promote the photoexciton dissociation, but also a reduced effective bandgap to enhance light absorption. More importantly, the interfacial dipole can facilitate the separation of carriers into different layers, thereby promoting carrier separation; and the intrinsic dipole across the Janus structure can drive photoinduced electron and hole transfer to opposite layers, enhancing carrier transport. We illustrate the concept in titanium-based Janus monolayer homojunction, where the theoretically observed PCE reaches 23.22% of TiSSe homojunction. In contrast to the previous cell architectures that require complex processing procedures and often result in defects, the doping-free homojunction configuration promises both high PCE and significantly lower manufacturing costs. Our work opens an avenue to design low-cost, high-efficiency solar cells.

Interface dipole evolution from the hybrid coupling between nitrogen-doped carbon quantum dots and polyethylenimine featuring the electron transport thin layer at Al/Si interfaces

The assessment of electron transport layer (ETL) for rear-contact engineering of silicon (Si) based optoelectronics has been considered as one of the critical challenges that leverage the performance improvement and device reliability. In this work, the hybrid design of ETL, obtained from the solution-processed nitrogen-doped carbon quantum dots (NCQDs) incorporated with organic polyethylenimine (PEI) demonstrates the feasible contact characteristics for the modification of Si/Al contacts, which greatly facilitates the transport and collection of photoexcited electrons in the Si-based optoelectronics. The aspects of microstructures, functional groups, chemical features, interfacial characteristics and band structures of NCQD/PEI are explicated, visualizing that the evolution of interface dipoles mediated by the overall outcome of physisorption and chemisorption effects, modifies the surface potential difference and results in the explicit reduction of the Al work function from 4.3 eV for pristine Al to 3.23 eV based on the optimized constitutional design (0.10 % NCQD in PEI). These findings are practically employed on the Si-based hybrid solar cells at Si/Al interfaces, fulfilling the conversion-efficiency improvement by 30.9 % compared with reference cells without ETL employment, which are experimentally interpreted by the efficient electron transport across the Si/Al heterojunction and charge collection.

Creation and Control of Lateral Electronic Junction in Ultrathin Semiconductor through the Interfacial Treatment Using Self-Assembled Monolayer

Interface engineering is essential to enhance the performance and stability of layered devices by resolving the interfacial issues, which dominantly affect the operation of the device. Unlike the interface, the adjoining bulk semiconductor is slightly affected by the interfacial treatment, and it is generally considered negligible in the classical semiconductor device theory. On the other hand, this interfacial effect is no longer trivial at the devices composing ultrathin layers, which are crucial for developing next-generation electronics with high integrity and low power consumption. Even though the semiconductors with tens of nanometers thickness, mainly used in current silicon-based industries, are significantly affected by the surrounding interfaces, however, this prominent interfacial influence is still underestimated. Herein, we show the substantial interfacial impact on the ultrathin semiconductor by the self-assembled monolayer (SAM) deposition, the p- to n-type inversion of the 50 nm silicon. The type and majority carrier density of the 50 nm silicon were determined by the interfacial dipole effect of SAMs according to their direction and strength, which was verified by Hall measurement and surface analysis such as UPS, XPS, and KPFM. As an interface engineering approach, the incorporation and control of SAMs show the potential as a simple alternative to the traditional impurity doping methods, which have difficulty in regulating the randomly distributed dopant in the case of the semiconductors with nanoscale thickness thereby causing unstable performance. Furthermore, we engineer the lateral electronic junction of the 50 nm silicon through the regioselective deposition of SAMs with opposite interfacial dipole, locally inducing p- and n-type silicon at each SAM-deposited region. Due to the presence of a lateral electronic junction, the 50 nm silicon exhibits the rectification behavior, which is reminiscent of a p-n diode. When we modulate the interfacial dipole of each SAMs through the ion pairing method using solutions of varying pH levels, the rectification ratio is sensitively changed. Therefore, the 50 nm silicon treated with the regioselective SAM deposition shows applicability as a pH sensing platform.

Fine-Tuning Hole Collection Via Self-Assembled Monolayers for Advancing Versatile Platforms

Recent advancements in transparent electronic devices have generated substantial research interest in transparent electrodes. Indium-tin-oxide (ITO) electrodes are widely utilized due to their high transmittance and low sheet resistance. However, their relatively low work function (WF) (< 5.0 eV) limits effective hole injection, necessitating methods to enhance the WF for improved energy alignment.To overcome these challenges, self-assembled monolayer (SAM) treatment offers a promising solution by combining low-temperature deposition, precise adsorption, and film thickness control at the angstrom scale, enhancing the WF of electrode surfaces by adjusting the molecular polarity within the SAM. This method significantly improves interfaces in electronic devices, optimizing charge transport and reducing recombination.This study investigates the effect of [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) derivatives—MeO-2PACz, 2PACz, and Br-2PACz—on the WF of ITO electrodes. The derivatives adsorbed onto the ITO surface, forming interfacial dipoles through chemisorption, thereby increasing the WF. Theoretical calculations and experimental analyses confirmed these WF variations, demonstrating that Br-2PACz significantly increased the WF due to its higher dipole moment. These findings suggest potential applications of chemisorption and explore the feasibility of this approach across various domains.The WF of ITO electrodes treated with 2PACz derivatives was measured using ultraviolet photoelectron spectroscopy and Kelvin probe, and validated through density functional theory calculations. The WF values for ITO, ITO/MeO-2PACz, ITO/2PACz, and ITO/Br-2PACz were 4.74, 4.81, 5.30, and 5.43 eV, respectively. This increase is attributed to the induced dipole moments of the derivatives. Atomic force microscopy showed that 2PACz derivatives treatment slightly reduced the surface roughness of ITO, indicating a more uniform surface. The root mean square roughness decreased from 1.056 nm for bare ITO to 0.912 nm for ITO/MeO-2PACz, 0.909 nm for ITO/2PACz, and 0.908 nm for ITO/Br-2PACz. This improvement in uniformity is crucial for enhancing device performance.Among them, the treatment with Br-2PACz notably enhanced the properties of electrodes used in indoor organic photovoltaics (OPVs) and metal-insulator-metal (MIM) capacitors.The indoor OPV device performance under artificial light was assessed with 2PACz derivatives-treated ITO electrodes. The devices used a polymer donor (PM6) and an NFA-based acceptor (Y6). Absorption spectra and energy band diagrams demonstrated effective photon absorption and energy level alignment. The Br-2PACz-based indoor OPV achieved a PCE of 31.0% and an excellent fill factor of 78.0% under LED 1000lx illumination, outperforming other variants due to improved hole injection and electron blocking from the higher WF.The Br-2PACz-based MIM capacitors demonstrated significant improvements in capacitance and leakage current reduction. Br-2PACz-treated capacitors exhibited the highest capacitance density and lowest dissipation factor, indicating low series resistance. The leakage current at 2 V was 0.88 nA/cm² for Br-2PACz-treated devices, 19,000 times lower than TiN-based capacitors. The increased WF achieved through 2PACz derivatives treatment enhances the barrier height between the TiO2 dielectric and electrode, thereby reducing leakage current.In conclusion, ultra-thin SAM treatment with 2PACz substituents effectively enhances electrode WF, thereby improving the performance of indoor OPVs and MIM capacitors. Br-2PACz, in particular, shows promise for high-efficiency, low-leakage applications, demonstrating significant potential for advancing electronic device performance through refined energy-level alignment. By manipulating the WF, this method presents a promising pathway to fine-tune the energy-level alignment in hybrid organic–inorganic electronic devices, thereby augmenting overall device performance

(Invited) Applications of Oxygen Inserted Epitaxy

Silicon remains the semiconductor material of choice for most electronic applications of semiconductors and the silicon–silicon dioxide interface is one of the most studied interfaces. Over the past decade or more, epitaxial silicon-germanium (eSiGe) has found increasing applications in advanced logic, first for PMOS compressive source-drain (S/D) stressors, then as a channel material in high-k metal gate (HKMG) devices to help control the PMOS Vt, and more recently as a sacrificial layer to enable stacked nanosheets and even as a S/D liner to reduce phosphorus diffusion into the undoped nanosheets. Oxygen inserted (OI) silicon epitaxy was originally developed to complement and bridge the gap between silicon and silicon-germanium, and it has found applications ranging from improved figure of merit power devices to the most advanced nanosheet applications. In this paper we will provide an overview of OI silicon devices, their fundamental characterization and the electrical and physical benefits offered for a variety of semiconductor applications. Introduction Oxygen-inserted (OI) silicon had an unusual genesis for a semiconductor material, in that it was first explored using ab-initio quantum mechanical simulation. It was found that by carefully inserting a partial monolayer of oxygen during silicon epitaxy a stable layer could be manufactured where the individual oxygen atoms arranged themselves on a silicon-silicon bond, but that overall, the silicon retained its regular lattice, and the silicon-oxygen coordination was only one, as opposed to four in regular silicon dioxide. The idealized lattice configuration is shown in Fig. 1 (a). This configuration is technically thermodynamically metastable, but with a significant energetic barrier to formation of four-fold coordinated silicon dioxide, so that it can survive conventional semiconductor processing. Whereas a single oxygen atom is known to rapidly diffuse in silicon, there is a thermodynamic self-stabilization when the oxygen concentration has an aerial density of the order of 1E15cm-2, with an upper limit dependent both on the specific epitaxial recipe and the required defect density. If all available silicon bonds have attached oxygen, it is difficult to maintain high quality epitaxy. On the other hand, OI silicon has passed the most rigorous defect density requirements for advanced logic applications. Dopant engineering - simulation Oxygen is highly electronegative, and ab initio simulation shows that there is charge transfer in the silicon lattice in the near vicinity of the inserted oxygen as shown in Fig 1 (b). This leads to a change in the formation enthalpy for a single substitutional dopant atom or addition of a silicon point defect, vacancy or interstitial as shown in Fig 1 (c). The figure indicates that substitutional boron and phosphorus will have an energetic preference to be two or three silicon lattice atoms away from the inserted oxygen, whereas silicon point defects prefer to be coincident with the oxygen. As a result, the OI layers disrupt the diffusion of dopant-interstitial pairs, substantially reducing the dopant diffusion. Dopant engineering – experimental data OI silicon has been proven to create unique abrupt doping profiles for a variety of silicon and silicon germanium devices. In power devices, reducing the vertical and lateral diffusion below the OI silicon layer can be used to engineer significant improvement in critical figures of merit, such as the tradeoff between specific ON resistance (Rsp) and the breakdown voltage, and improved time constant (Ron∙ Coff) and reduced body current in RF power devices, while maintaining breakdown voltage. In advanced 3D applications, a 2nm thin liner of OI silicon has proven effective to create a diffusion barrier between highly doped epitaxial source/drain regions and undoped channels. By reducing dopant up-diffusion, thermally robust super-steep retrograde profiles can be created, which can be used to reduce local threshold voltage mismatch in both NMOS and PMOS devices by more than 50%. In gate-first HKMG planar CMOS applications, SiGe channel is used in the PMOS to facilitate Vt engineering. A thin OI silicon layer below the SiGe channel can be used to maintain a super-steep retrograde channel profile after HKMG formation and subsequent thermal processing. Interface interactions It has recently been discovered that OI silicon can also be used to engineer adjacent interfaces. For example, it has been shown by cryogenic measurements that OI silicon reduces surface roughness scattering of the silicon-dielectric interface. Also, OI silicon can reduce the interfacial dipole formed during HKMG processing, with benefits in reduced remote charge scattering and improved reliability.These and other examples of engineered silicon and silicon-germanium devices will be discussed in detail. Figure 1

Carbon monochalcogenides/graphene van der Waals heterostructures for sustainable energy harvesting

We constructed the van der Waals (vdW) heterostructures by stacking graphene (G) on top of carbon-based monochalcogenides (CX; X = S, Se, and Te) monolayer in two different patterns (I and II) and predicted various physical properties through first-principles calculations. Among the six heterostructures, three systems (CS/G in Pattern-I and II, and CSe/G in Pattern-II) were found to be most stable. Additionally, the calculated electronic properties confirmed that the CS/G and CSe/G heterostructures in Pattern II are indirect semiconductors with narrow band gap values of 0.49 and 0.30 eV, respectively. Notably, both heterostructures (CS/G and CSe/G) exhibit significantly larger electron carrier mobilities of 762.83 and 206.84 m2/Vs at room temperature, respectively. Furthermore, intrinsic and interface dipoles in both heterostructures were found to align along the +z axis, enhancing charge transfer at the interface and narrowing the band gap, particularly in CSe/G. This polarization effect contributes to the observed high electron mobility and thermoelectric performance. Electronic transport coefficients like the Seebeck coefficient, electrical conductivity, and thermoelectric power factor are predicted using the Boltzmann transport theory implemented in the BoltzTrap code. The highest power factor 249mW/mK2 was achieved for the CSe/G heterostructure at 300K, demonstrating its ability for good thermoelectric purposes. Besides, the computed optical properties revealed the potential of the CS/G heterostructure as a light absorber with an excellent solar light energy conversion efficiency (η) of 23.57 % for solar cell device applications. Our predictions show that the novel 2D CX/G vdW heterostructures could be promising candidates for designing new solar and heat energy harvesting devices.

Dual‐Site Anchors Enabling Vertical Molecular Orientation for Efficient All‐Perovskite Tandem Solar Cells

AbstractAll‐perovskite tandem solar cells (TSCs) are gaining increasing attention due to their potential to surpass the efficiency limit of single‐junction solar cells. However, as the bottom low‐bandgap subcells, tin‐lead (Sn‐Pb) perovskites suffer from severe nonradiative recombination at the interfaces due to their susceptibility to oxidation and poor crystalline morphology. Here a surface modifier 4‐(trifluoromethyl)benzhydrazide (TFH) is reported to construct a reductive chemical environment on the surface of perovskite films and protect them from water and oxygen erosion. TFH anchors onto the Sn‐Pb perovskites in a preferred vertical orientation through dual‐site binding, forming interface dipoles that facilitate charge extraction. The reductive hydrazine groups of TFH can effectively inhibit the oxidation of Sn2+ and I−, thereby reducing the defect density and energy disorder of Sn─Pb perovskites. Consequently, the TFH‐treated devices achieved a champion PCE of 22.88%, maintaining over 93% of the initial efficiency after continuous one‐sun illumination for 500 h. Combined with a 1.79 eV wide‐bandgap subcell, it has demonstrated a PCE of 28.17% in all‐perovskite TSCs.

Facile synthesis of CoFe/C nanoparticle embedded in nitrogen and sulfur co-doped reduced graphene oxide nanocomposites for electromagnetic wave absorption

Three-dimensional metal–organic framework derivatives (MOFs) offer significant potential for the absorption of electromagnetic waves (EMW). However, the discrepancy in impedance matching restricts their ability to absorb EMW efficiently. This study synthesized a novel composite material, CoFe/C@N, S-rGO, by combining diazo coupling reactions, solvothermal techniques, and high-temperature pyrolysis. The composite consists of cobalt iron/carbon (CoFe/C) nanoparticles embedded in N and S co-doped reduced graphene oxide (N, S-rGO). The co-doping of N and S on graphene oxide (SGO) resulted in numerous defects and disordered sites, which generated interfacial and dipole polarization. The EMW absorption characteristics of the CoFe/C@N, S-rGO can be tuned by varying the quantity of SGO added. Notably, at an SGO concentration of 60 mg, the produced composite exhibits a minimal reflection loss of −53.8 dB, while a thickness of 4.0 mm yields an effective absorption bandwidth of 7.2 GHz. This material’s exceptional EMW absorption capabilities are primarily attributed to interface polarization, multiple reflections, dipole polarization, natural resonance, and eddy current loss. The findings of this study provide a potential solution for enhancing the impedance matching and electromagnetic wave absorption performance of MOFs.