Effective Surface Passivation Research Articles

Sustainable solar-powered hydrogen generation with a silicon nanopillar device with a low carbon footprint

A device system enabling continual hydrogen production under solar light in a water environment is proposed in this study. This system features a self-powered water splitter with a solar harvester from an aluminium-doped zinc oxide/n-type silicon Schottky junction. Thin-film photovoltaic devices are connected in series to reach the reaction potential necessary for the electrolysis of water. Three types of device systems are studied, and their respective hydrogen generation properties are evaluated. The surface passivation effect from only 0.8 nm ultrathin aluminium oxide was found to effectively protect the device surface by withstanding the corrosion of critical solutions for hydrogen generation. In addition, the surface silicon nanopillars create numerical Schottky junctions that can reduce the reaction potential for the electrolysis of DI water from 1.28 V to 0.74 V and achieve a 115 μLh−1cm−2 hydrogen generation rate. Here, a bias-free and simple structural device system is successfully developed and is advantageous for directly converting solar energy into hydrogen among various water systems. The idea of a sustainable solar-powered hydrogen generation system as well as a future low-carbon footprint design meets the principles of the Paris Agreement.

Boosting the Carrier Lifetime and Optical Activity of CsPbX3 Nanocrystals through Aromatic Ligand Passivation.

Ligand engineering is crucial for tuning the structural and optoelectronic properties of perovskite nanocrystals (NCs), which also improves their stability. In contrast to the typically used long-chain alkylamine ligands, we successfully introduced an aromatic 1-(p-tolyl)ethylamine (PTEA) ligand to synthesize the CsPbX3 (X = Br or I) NCs. The CsPbI3 and CsPbBr3 NCs demonstrated long carrier lifetimes of ∼877 and 49 ns, respectively, as well as high photoluminescence quantum yields (PLQYs) of ∼99% and 95%, respectively. Furthermore, such NCs realized excellent long-term stability in an ambient atmosphere without obvious degradation over one month. All of these properties were better than the properties of NCs coated with the conventional alkylamine ligands. The high performance of these NCs was discussed with the effective surface passivation by PTEA. Our finding suggests a facile and effective ligand (PTEA) for modulating perovskites, achieving enhancement of both the carrier lifetime and the PLQY.

Harnessing Pb-S Interactions for Long-Term Water Stability in Cesium Lead Halide Perovskite Nanocrystals.

Lead halide perovskite nanocrystals (LHP NCs) have garnered attention as promising light-harvesting materials for optoelectronics and photovoltaic devices, attributed to their impressive optoelectronic properties. However, their susceptibility to moisture-induced degradation has hindered their practical applications. Despite various encapsulation strategies, challenges persist in maintaining their stability and optoelectronic performance simultaneously. Here, a ligand exchange approach is proposed using (11-mercaptoundecyl)-N,N,N-trimethylammonium bromide (MUTAB) to enhance the stability and dispersibility of CsPbBr3 (CPB) NCs in aqueous environments. MUTAB enables effective surface passivation of the CPB NCs via robust Pb-S interactions at the S-terminal while concurrently directing water molecules through the unbound cationic N-terminal or vice versa, ensuring water dispersibility and stability. Spectroscopic analysis confirms retained structural and optical integrity post-ligand exchange. Crucially, MUTAB-bound CPB NCs exhibit sustained charge transfer properties, demonstrated by aqueous colloidal oxidation reactions. This ligand exchange strategy offers a promising pathway for advancing LHP NCs toward practical optoelectronic and photocatalytic applications.

Effective surface passivation for stable and high-performance inverted CsPbI2Br perovskite solar cells with efficiency over 15%

Inverted CsPbI2Br perovskite solar cells (PSCs) still suffer from substantially non-radiative recombination losses at the perovskite interface, which limits the future advancement of CsPbI2Br perovskite-based single- and multi-junction photovoltaic cells. Interfacial defect passivation of perovskite films is an effective approach for enhancing the performance of PSCs. In this study, we introduce thiophene halide salts with different side groups on the surface of CsPbI2Br films to passivate the inorganic perovskite film and investigate their passivation effects. Our studies show that the 2-thiophenemethylammonium iodide (TM) passivator with –CH2NH3I side group effectively mitigates the trap density of the perovskite film by forming coordination bonding with Pb2+ ions, thus significantly inhibiting the non-radiative recombination in the resulting PSC. In addition, after the TM treatment, the better energy-level alignment between the CsPbI2Br/[6,6]-Phenyl C61 butyric acid methyl ester (PCBM) interface is achieved, thus enhancing the charge extraction from perovskite to the charge transport layer. The resulting inverted CsPbI2Br device demonstrates a significantly enhanced champion efficiency of 15.07% with a Voc of 1.16 V, Jsc of 16.42 mA/cm2, and FF of 79.11%, compared to the 11.19% efficiency of the control device, and maintains >97% of the initial efficiency after being stored for over 1700 h in N2 atmosphere. This work confirms the importance of substituent groups on surface passivation molecules for effective passivation of defects and optimization of energy levels, particularly for Voc improvement.

Short-branched alkyl sulfobetaine-passivated CsPbBr3 nanocrystals for efficient green light emitting diodes.

Inorganic cesium lead bromide nanocrystals (CsPbBr3 NCs) hold promising prospects for high performance green light-emitting diodes (LEDs) due to their exceptional color purity and high luminescence efficiency. However, the common ligands employed for passivating these indispensable NCs, such as long-chain organic ligands like oleic acid and oleylamine (OA/OAm), display highly dynamic binding and electronic insulating issues, thereby resulting in a low efficiency of the as-fabricated LEDs. Herein, we report a new zwitterionic short-branched alkyl sulfobetaine ligand, namely trioctyl(propyl-3-sulfonate) ammonium betaine (TOAB), to in situ passivate CsPbBr3 NCs via a feasible one-step solution synthesis, enabling efficiency improvement of CsPbBr3 NC-based LEDs. The zwitterionic TOAB ligand not only strengthened the surface passivation of CsPbBr3 NCs with a high photoluminescence quantum yield (PLQY) of 97%, but also enhanced the carrier transport in the fabricated CsPbBr3 NC thin films due to the short-branched alkyl design. Consequently, CsPbBr3 NCs passivated with TOAB achieved a green LED with an external quantum efficiency (EQE) of 7.3% and a maximum luminance of 5716 cd m-2, surpassing those of LEDs based on insulating long-chain ligand-passivated NCs. Our work provides an effective surface passivation ligand design to enhance the performance of CsPbBr3 NC-based LEDs.

Enhancing minority carrier lifetime in Ge: Insights from HF and HCl cleaning procedures

Efficiently passivating germanium (Ge) surfaces is crucial to reduce the unwanted recombination current in high-performance devices. Chemical surface cleaning is critical to remove surface contaminants and Ge oxides, ensuring effective surface passivation after dielectric deposition. However, Ge oxides can rapidly regrow upon air exposure. To understand the surface evolution after wet cleaning, we present a comprehensive study comparing HF and HCl deoxidation steps on p-type Ge surfaces and monitor the surface as a function of air exposure time. Distinct oxide regrowth dynamics are observed: HF-treated samples exhibit swift regrowth of all Ge oxide states, whereas HCl-treated Ge surfaces exhibit a lower concentration of low degrees of oxidation and slower or no regrowth of high oxide states even after 110 min of air exposure. In addition, the presence of Ge–Cl bonds induces different oxidation dynamics compared to the Ge–OH bonds resulting from HF cleaning. This leads to varying surface electronic band structures, with HF-treated Ge exhibiting a strong positive band bending (+0.20 eV). Conversely, HCl-treated samples display a lower band curvature (+0.07 eV), mostly due to the presence of Ge–Cl bonds on the Ge surface. During air exposure, the increased GeOx coverage significantly reduces the band bending after HF, while a constant band bending is observed after HCl. Finally, these factors induce a reduction in the surface recombination velocity after wet etching. Combining both chemical and field-induced passivation, HF-treated Ge without rinsing exceeds 800 μs.

Passivation-Free, Liquid-Metal-Based Electrosynthesis of Aluminum Metal-Organic Frameworks Mediated by Light Metal Activation.

The production of aluminum (Al) metal-organic frameworks (MOFs) by electrosynthesis using solid-state Al electrodes always faces significant challenges due to the formation of a passivating aluminum oxide layer in the process. Here, we developed a liquid-metal-based method to electrosynthesize an aluminum Al-MOF (MIL-53). This method uses a liquid-state gallium (Ga) anode as a reservoir and activator for a light metal, Al, in the form of Al-Ga alloys that releases Al3+ for the electrosynthesis of Al-MOFs. Introducing Ga into the system inhibits the formation of aluminum oxide passivation layer and promotes the electrochemical reaction for Al-MOF synthesis. The electrosynthesis using liquid Al-Ga alloy is conducted at ambient temperatures for long durations without requiring pretreatment for aluminum oxide removal. We show that the Al-MOF products synthesized from 0.40 wt % Al in liquid Ga lead to the highest crystallinity and possess a specific surface area greater than 800 m2 g-1 and a low capacity for CO2 adsorption that can be used as a potential matrix for CO2/N2 separation. This work provides evidence that employing liquid-metal electrodes offers a viable pathway to circumvent surface passivation effects that inevitably occur when using conventional solid metals. It also introduces an efficient electrosynthesis method based on liquid metals for producing atomically porous materials.

Asymmetric Metal–Semiconductor–Metal Al0.24Ga0.76N UV Sensors with Surface Passivation Effect Under Local Joule Heating

Asymmetric Metal–Semiconductor–Metal Al0.24Ga0.76N UV Sensors with Surface Passivation Effect Under Local Joule Heating

Benzothieno[3,2-b]thiophene-Based Noncovalent Conformational Lock Achieves Perovskite Solar Cells with Efficiency over 24.

Organic semiconductors with noncovalently conformational locks (OSNCs) are promising building blocks for hole-transporting materials (HTMs). However, lack of satisfied neighboring building blocks negatively impacts the optoelectronic properties of OSNCs-based HTMs and imperils the stability of perovskite solar cells (PSCs). To address this limitation, we introduce the benzothieno[3,2-b]thiophene (BTT) to construct a new OSNC, and the resulting HTM ZS13 shows improved intermolecular charge extraction/transport properties, proper energy level, efficient surface passivation effect. Consequently, the champion devices based on doped ZS13 yield an efficiency of 24.39 % and 20.95 % for aperture areas of 0.1 and 1.01 cm2 , respectively. Furthermore, ZS13 shows good thermal stability and the capability of inhibiting I- ion migration, thus, leading to enhanced device stability. The success in neighboring-group engineering can triggered a strong interest in developing thienoacene-based OSNCs toward efficient and stable PSCs.

Benzothieno[3,2‐b]thiophene‐Based Noncovalent Conformational Lock Achieves Perovskite Solar Cells with Efficiency over 24 %

AbstractOrganic semiconductors with noncovalently conformational locks (OSNCs) are promising building blocks for hole‐transporting materials (HTMs). However, lack of satisfied neighboring building blocks negatively impacts the optoelectronic properties of OSNCs‐based HTMs and imperils the stability of perovskite solar cells (PSCs). To address this limitation, we introduce the benzothieno[3,2‐b]thiophene (BTT) to construct a new OSNC, and the resulting HTM ZS13 shows improved intermolecular charge extraction/transport properties, proper energy level, efficient surface passivation effect. Consequently, the champion devices based on doped ZS13 yield an efficiency of 24.39 % and 20.95 % for aperture areas of 0.1 and 1.01 cm2, respectively. Furthermore, ZS13 shows good thermal stability and the capability of inhibiting I− ion migration, thus, leading to enhanced device stability. The success in neighboring‐group engineering can triggered a strong interest in developing thienoacene‐based OSNCs toward efficient and stable PSCs.

Water-Mediated Conversion of BaTiO3 Nanoparticles into BaCO3 Nanorods in Electrospun Polymer Fibers: Implications for Carbon Capture Applications.

Under ambient conditions and in aqueous environments, transformations of nanoparticle-based ferroelectric components can raise important stability issues that are relevant for applications as multilayer capacitors, flexible piezoelectrics, or biomedical devices. We show that X-ray amorphous BaTiO3 nanoparticles that were grown by flame spray pyrolysis and which can be incorporated into electrospun polymer fibers undergo incongruent Ba2+ dissolution in the presence of water. At pH > 5 and in contact with air, corresponding Ba solutes spontaneously convert into crystalline BaCO3 needles to produce characteristic nano- and microstructures. We compared the reactivity of amorphous BaTiO3 nanoparticle powders with those of nanocrystals after annealing-induced crystallization. The stability of aqueous nanoparticle-polymer formulations, which are typically part of nanoparticle encapsulation in polymers and electrospinning, was included in this analysis. Nanoparticle size, crystallinity, surface area, the presence of carbonaceous surface contaminants, and the effect of surface passivation with polymers are addressed to underline the critical role of condensed water during the synthesis, storage, and processing of BaTiO3 nanoparticle-based composites.

Diameter and gap controlled fabrication of periodic SiMW/SiNW arrays: A broadband absorber for high efficiency silicon solar cell

Vertically aligned and periodic silicon micro/nano-wire (SiMW/SiNW) arrays of different diameters were synthesized by combining lithography-free silica particle patterning, reactive ion etching (RIE), and modified metal-assisted chemical etching (MACE) methods. All required silica particles were synthesized, and process parameters were optimized to fabricate sub 50 nm SiNW to large size SiMW with the controlled inter-wire gap. Fabricated SiMW/SiNW array samples show a significant reduction of reflectance (7–9 %) in the silicon absorption band (300 nm–1000 nm). Additional absorption of 25–33 % compared to the planar silicon is observed in the sub-bandgap region of silicon (1100–2000 nm) for these samples, which signifies the effect of field confinement within these structures. The estimated short circuit current density (JSC) using the experimental absorption spectrum of SiMW is 49.96 mA/cm2, which is 16 % higher than the Lambertian limit of ∼43 mA/cm2. This result can lead to the theoretical efficiency of the solar cell up to 28.73 % without the inclusion of the surface passivation effect.

Adequate method to study the surface passivation effectiveness in HEM multicristallin silicon wafers

In this work we have examined the effectiveness of surface passivation on ascut multicrystalline silicon (mc-Si) wafers using different techniques. The study is based on minority carrier lifetime measurements with quasi steady state photo-conductance, ‘QSSPC’. Effective minority carrier lifetime ()measured values of 12.4, 8.9, 4.9 and 3.1 are obtained respectively with four silicon surface passivation techniques: 1- Shallow phosphorous diffusion emitter (n+p), 2- Iodine-Ethanol (I-E), 3-Hydrofluoric acid (HF) emersion and 4-SiNx layer deposition. These results suggest that the shallow n+p emitter gives the eff close to the bulk lifetime due to the better surface passivation quality. Simulations made with Hornbeck-Haynes model indicate that the improvement can be correlated with the decrease of the surface recombination velocity (SRV) and the increment of bulk lifetime.

Macroscale ultradurable superlubricity on passivated transition-metal diborides

Superlubricity is a sliding regime with almost vanishing friction sustained under stringent material conditions. This remarkable phenomenon was first found between surfaces with incommensurate lattice structures, and later extended to materials with weak shear, as in many two-dimensional layered materials. Such materials, however, face great challenges that limit their applications, including the difficulty to scale up to meet the needs of many practical implementations and low durability stemming from the intrinsic structural weakness. Overcoming these limitations hinges on new design and fabrication of advanced superlubricating materials. Here, we report on the realization of macroscale ultradurable superlubricity on passivated transition-metal diborides (TMB2) following an unconventional design principle that first construct materials with strong anti-wear ability then create superlubricity via effective surface passivation. TMB2 possess superior mechanical strength and durability, along with the ability to activate in-situ load-induced passivation layers via tribochemical actions at the surface. The resultant passivated TMB2 exhibits characteristic superlubricating and ultradurable friction coefficient (0.002) and wear rate (10−19 m3/N·m). These findings introduce a fresh approach toward rational design and implementation of superlubricating materials, opening a new avenue for versatile applications at large (up to industrial) scales.

Effect of stress modulation of Al2O3 and Si3N4 nanolayers on the photoelectric properties of ReS2 photodetectors based on sapphire substrates

Atomic layered material is a particular candidate for adjusting the energy band structure of semiconductor materials through strain engineering, which is an effective and convenient method to improve photoelectric performance. Herein, we demonstrated the ReS2-based photodetectors covered with high-k Al2O3 and Si3N4 stress layers. The stress layers photodetectors show excellent thermal stability due to the surface passivation effect of the dielectric layers and high optoelectronic properties due to the doping effect formed upon laser excitation. In addition, the presence of the stress layer causes tensile strain in the ReS2 film, which alters its energy band structure properties. Through the first-principles calculations, it can be found that the band gap and the electron effective mass of ReS2 have decreased with the increase of the tensile stress, which further increases the carrier mobility. In addition, photodetectors with Al2O3 and Si3N4 stress layers were prepared separately, and the significant enhancement of the photoelectric performance of ReS2 devices by deposited stress layers was demonstrated.

Divergence in Antiviral Activities of Carbon Dots versus Nano-Carbon/Organic Hybrids and Implications

Carbon dots (CDots) are generally defined as small carbon nanoparticles (CNPs) with effective surface passivation, for which the classical synthesis is the functionalization of pre-existing CNPs with organic molecules. However, “dot” samples produced by “one-pot” thermal carbonization of organic precursors are also popular in the literature. These carbonization-produced samples may contain nano-carbon domains embedded in organic matters from the precursors that survived the thermal processing, which may be considered and denoted as “nano-carbon/organic hybrids”. Recent experimental evidence indicated that the two different kinds of dot samples are largely divergent in their photo-induced antibacterial functions. In this work, three representative carbonization-produced samples from the precursor of citric acid–oligomeric polyethylenimine mixture with processing conditions of 200 °C for 3 h (CS200), 330 °C for 6 h (CS330), and microwave heating (CSMT) were compared with the classically synthesized CDots on their photo-induced antiviral activities. The results suggest major divergences in the activities between the different samples. Interestingly, CSMT also exhibited significant differences between antibacterial and antiviral activities. The mechanistic origins of the divergences were explored, with the results of different antimicrobial activities among the hybrid samples rationalized in terms of the degree of carbonization in the sample production and the different sample structural and morphological characteristics.

Study on the influence of micro-alkali texturing and micro-alkali polishing process on the passivation and contact performance of n-TOPCon solar cells

The matching between the morphology of the backside of n-TOPCon solar cells and the tunnel oxide/n + polysilicon structure is the key to achieving high efficiency. In this work, based on the requirement of edge isolation, micro-alkali polishing and micro-alkali texturing were performed on the acid-polishing back surface. Their effects on surface morphology, passivation effect, contact resistance, and photoelectric conversion efficiency were investigated. Adding a short-time micro-alkali texturing process after acid polishing can form a surface morphology with both regional polishing and local microtexture. This can improve the contact characteristics without significantly affecting the passivation characteristics, enabling solar cells to achieve higher FF (83.30%) and average efficiency (24.15%). Compared with the acid polishing sample, the efficiency of the micro-alkali texturing sample is increased by 0.12%. The deterioration of ohmic contact caused by alkali polishing has not been eliminated by optimizing the reaction process of alkali polishing. The study of different surface morphologies-modified samples under different tunnel oxide layer growth time, also reveals the difference in the influence of tunnel oxide layer characteristics on samples with different morphologies. The acid-polishing samples show more stable FF and conversion efficiency at different thermal oxidation time, and the micro-alkali texturing samples have a significant FF advantage at shorter thermal oxidation time. These studies can be applied and validated in the photovoltaic industry.

Accurate Multiscale Simulation of Frictional Interfaces by Quantum Mechanics/Green's Function Molecular Dynamics.

Understanding frictional phenomena is a fascinating fundamental problem with huge potential impact on energy saving. Such an understanding requires monitoring what happens at the sliding buried interface, which is almost inaccessible by experiments. Simulations represent powerful tools in this context, yet a methodological step forward is needed to fully capture the multiscale nature of the frictional phenomena. Here, we present a multiscale approach based on linked ab initio and Green's function molecular dynamics, which is above the state-of-the-art techniques used in computational tribology as it allows for a realistic description of both the interfacial chemistry and energy dissipation due to bulk phonons in nonequilibrium conditions. By considering a technologically relevant system composed of two diamond surfaces with different degrees of passivation, we show that the presented method can be used not only for monitoring in real-time tribolochemical phenomena such as the tribologically induced surface graphitization and passivation effects but also for estimating realistic friction coefficients. This opens the way to in silico experiments of tribology to test materials to reduce friction prior to that in real labs.

Self-healing in CdTe nanostructures: Insights into their structural stability and optical properties using first principles theory

Herein, we report a first-principle density functional theory-based study on CdTe nanostructures in 1D (nanorods and nanotubes) and 2D (ultra-thin slabs, monolayers) systems created within the top-down approach in terms of various properties, such as electronic structure, structural stability, and optical properties, and the effect of surface passivation on these properties. A substantial quantum confinement effect is observed with the increase in the energy band gap observed when the thickness or diameter of the nanostructure becomes less than the excitonic Bohr radius of CdTe. For all of the nanostructures studied, the structural stability improves upon surface passivation. The dielectric properties suggest that all of the passivated and specific unpassivated nanostructures are suitable for optoelectronic applications. Among the nanostructures studied, the 2D system prepared in the <110> orientation and the nanotube derived from the <111> monolayer are the most stable and show the least enhancement (0.1–0.2 eV) in the energy band gap upon passivation. This minimal change may be due to significant self-healing in the pristine structures. The charge density plots obtained for the relaxed and unrelaxed pristine structures show the surface had undergone reconstruction as a self-healing mechanism. The stability, self-healing ability, and energy bandgap of these nanostructures suggest their applicability in optoelectronic devices.

Device engineering of p-CuAlO2/β-Ga2O3 interface: A staggered-gap band-alignment

In this work, by controlling the oxygen flow rate (OFR) (from 0% to 30%), we suggest using a p-type copper aluminum oxide (p-CuAlO2) interlayer to enhance the high breakdown and low leakage current for β-Ga2O3-based power device applications. Results of AFM measurements on p-CuAlO2 films performed using various OFRs demonstrate that greater OFRs result in an increase in film roughness payable to the unavoidable leading of defects/oxygen vacancy (VO). We used XPS and TEM analysis to validate the surface elemental compositions, chemical states, band offsets and microstructural properties of p-CuAlO2/β-Ga2O3 heterojunction (HJ) with different OFRs. With increasing OFR from 0% to 17.6%, the VBO and CBO values of HJ were decreased from 1.73 eV to 1.23 eV and from 0.53 eV to 0.38 eV respectively. Then, with increasing OFR from 17.6% to 30%, VBO was decreased from 1.23 eV to 1.13 eV while CBO increased from 0.38 eV to 0.58 eV. The staggered-gap (type-II) across the p-CuAlO2/β-Ga2O3 HJ is identified the entire OFRs. The rising tendency of optical bandgap (Eg) of p-CuAlO2 with range of OFRs, a maximum Eg of 4.35 eV was obtained with OFR of 30%. Furthermore, the electrical and carrier transport properties of p-CuAlO2/β-Ga2O3 HJ were studied using I–V and C–V techniques. The reverse breakdown voltage (Vbr) of HJ is strongly dependent on OFRs. With increasing OFRs, Vbr was decreased from 937 V to 924 V, and then to 1000 V with increasing OFR from 0% to 17.6% and then to 30%. In addition, a decrease in the interface state density (NSS) with increasing OFRs was observed which indicates that oxygen may be an effective surface passivation. Analysis confirmed that Poole-Frenkel emission dominates the reverse leakage current of all the HJ samples. The type-II p-CuAlO2/β-Ga2O3 HJ may facilitate the design and manufacture of high-performance β-Ga2O3-based heterojunctions and advance optoelectronic devices.