Efficient Surface Passivation Research Articles

Near-infrared DNA biosensors based on polysulfonate coatings for the sensitive detection of microRNAs.

MicroRNAs (miRNAs) play crucial roles in the regulation of immune cell differentiation and the immune response during allergic rhinitis (AR). Studies have shown that miRNA-155 is significantly upregulated in AR pathogenesis. Therefore, miRNA-155 can be used as a biomarker for AR diagnosis. Although fluorescent biosensors based on upconversion nanoparticles (UCNPs) have made significant advances in the detection of miRNAs, developing UCNPs with polymer coatings, efficient surface passivation, and DNA functionalization for hybrid sensing in biological media remains challenging. Herein, hairpin DNA1 (H1) is modified into a thin polysulfonic acid layer on UCNPs by sulfonamide bonds, and the fluorescence of the UCNPs is quenched by the fluorescence resonance energy transfer (FRET) process of BHQ3 carried by H1. When the target miRNA-155 is present, the hairpin structure of H1 is opened, allowing BHQ3 to move away from the UCNP surface, and the fluorescence of UCNP is restored. At the same time, hairpin DNA1 (H2) can combine with H1 to replace the miRNA-155 that is bound to H1 with the help of the opening stem ring structure of H1, and the replaced miRNA-155 can continue to react with H1 to amplify the fluorescence signal. Under the optimal experimental conditions, the linear range of miRNA-155 is 0.01-3 nM, with a detection limit of 1.14 pM. Furthermore, the constructed biosensor has been applied to determine miRNA-155 in serum samples, and the spiked recoveries range from 99.8% to 104.8%, which indicates that the developed assay has potential applications in monitoring allergic rhinitis or other miRNA related diseases.

GaN Surface Passivation by MoS2 Coating.

In this study, we investigate the impact of two-dimensional MoS2 coating on the optical properties of surface GaN/AlGaN quantum wells (QWs). A strong enhancement in GaN QW light emission is observed with monolayer-MoS2 coating, yielding luminescence intensity comparable to that from a QW capped by an AlGaN barrier. Our results demonstrate that MoS2, despite its quite different nature from III-nitride semiconductors, acts as an effective barrier for surface GaN QWs and suppresses spatially localized intrinsic surface states. This finding provides novel pathways for efficient III-nitride surface passivation.

Efficient Surface Passivation of Ti-Based Layered Materials by a Nonfluorine Branched Copolymer for Durable and High-Power Sodium-Ion Batteries.

There is a crucial need for low-cost energy storage technology based on abundant sodium ions to realize sustainable development with renewable energy resources. Poly(vinylidene fluoride) (PVDF) is applied as a binder in sodium-ion batteries (SIBs). Nevertheless, PVDF is also known to suffer from a larger irreversible capacity, especially when PVDF is used as the binder of negative electrode materials. In this research, a poly(acrylonitrile)-grafted poly(vinyl alcohol) copolymer (PVA-g-PAN) is tested as a binder with Ti-based layered oxides as potential negative electrode materials for SIBs. The chemical stability tests of PVDF and PVA-g-PAN contacted with metallic sodium have been conducted, which reveals that PVDF experiences a defluorination process, while PVA-g-PAN demonstrates excellent chemical stability. Composite electrodes with PVA-g-PAN demonstrate superior electrochemical performances when compared with the PVDF binder, allowing improvement for initial CE, higher rate capability, and long cyclability over 1500 cycles. Detailed characterization of electrodes via soft X-ray photoelectron spectroscopy and field emission scanning electron microscopy demonstrates that the PVA-g-PAN branched structure allows a more uniform distribution of acetylene black with higher coatability, unlocking enhanced rate performances and efficient passivation of Ti-based oxides without the excessive electrolyte decomposition. These findings open a new way to design practical and durable sodium-ion batteries with a high-power density.

Contrasting the stability, octahedral distortions, and optoelectronic properties of 3D MABX3 and 2D (BA)2(MA)B2X7 (B = Ge, Sn, Pb; X = Cl, Br, I) perovskites.

Efficient surface passivation and toxic lead (Pb) are known obstacles to the photovoltaic application of perovskite-based solar cells. A possible solution for these problems is to use thin-films of two-dimensional (2D) perovskite-based materials and the replacement of Pb with alternative divalent cations (B); however, our atomistic understanding of the differences between (3D) three-dimensional and 2D perovskite-based materials is far from satisfactory. Herein, we report a systematic theoretical investigation based on ab initio density functional theory (DFT) calculations for both 3D MABX3 and the Ruddlesden-Popper 2D (BA)2(MA)B2X7 (B = Ge, Sn, Pb, and X = Cl, Br, I) compounds to investigate the differences (contrasts) in selected physical-chemical properties, i.e., structural parameters, energetic stability, electronic, and optical properties. We found an increased cation/anion charge separation because of the presence of organic spacers, which results in stronger Coulomb interactions in the inorganic framework, and hence, it enhances the cohesive energy (stability) within the inorganic layer. The inorganic layer constitutes the optically active region that contributes to the superior performance of perovskite-based solar cells. We quantified this effect by comparing the average electronic charges at the X sites in both 2D and 3D perovskites. This comparison is then correlated with variations in BX6-octahedron volumes, resulting in a monotonic relation. Moreover, the electronic structure characterization demonstrates that Ge-based systems present weakly sensitive band gaps to dimensionality due to a compensatory effect between Jahn-Teller distortions and quantum confinement. Lead-free GeI-, SnBr-, and SnI-based perovskites have DFT band gaps closer to the optimal value used in photovoltaic applications. Finally, as expected, the 2D systems absorption coefficients show pronounced anisotropy.

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.

Rational design of surface passivation for highly efficient quantum dot sensitized solar cell

Surface passivation of quantum dot sensitized photoanode is of significant importance to enhance the performance of quantum dot sensitized solar cell (QDSSC) by reducing the charge recombination at photoanode/electrolyte interface. In this paper, we report a rational way to design an efficient surface passivation to enhance the cell performance of QDSSC, based on the systematic study of the influence of the structure and properties of overcoating layers on the performance of QDSSC. CdSe/TiO2 prepared from a postsynthesis assembly approach was used as the photoanode film, while ZnS and ZnSe were used as the passivation materials to be deposited on CdSe/TiO2 via a successive ionic layer adsorption and reaction (SILAR) route. Investigations showed that, QDSSC overcoated with ZnS/ZnSe dual passivation layer strongly inhibited the charge recombination and thus achieved high power conversion efficiency of 6.83%, much higher than the cells without or with single ZnS or ZnSe overcoating as well as the dual passivation with reversed deposition sequence. Detailed analyses demonstrate that passivation of overcoating is closely related to the coverage of QDs on TiO2, the lattice parameters and band structure of QD, TiO2 and overcoating materials, and a rational design of the surface overcoating is crucial for enhancing the cell performance of QDSSC.

Acceleration of Near-IR Emission through Efficient Surface Passivation in Cd3P2 Quantum Dots.

Fast near-IR (NIR) emitters are highly valuable in telecommunications and biological imaging. The most established NIR emitters are epitaxially grown InxGa1-xAs quantum dots (QDs), but epitaxial growth has several disadvantages. Colloidal synthesis is a viable alternative that produces a few NIR-emitting materials, but they suffer from long photoluminescence (PL) times. These long PL times are intrinsic in some NIR materials (PbS, PbSe) but are attributed to emission from bright trapped carrier states in others. We show that Cd3P2 QDs possess substantial trap emission with radiative times >101 ns. Surface passivation through shell growth or coordination of Lewis acids is shown to accelerate the NIR emission from Cd3P2 QDs by decreasing the amount of trap emission. This finding brings us one step closer to the application of colloidally synthesized QDs as quantum emitters.

Synergistic Ion-Anchoring Passivation for Perovskite Solar Cells with Efficiency Exceeding 24% and Ultra-Ambient Stability.

The high-density defect states existing at the grain boundaries and heterojunction interfaces induce nonradiative charge recombination and ion migration processes within perovskite film, which seriously impair the device efficiency and stability. Here, we propose a novel synergistic ion-anchoring passivation (SIP) strategy for high-performance perovskite solar cells, by designing a multifunctional molecule to heal the charged defects via electrostatic interactions. The anion and cation species of the multifunctional molecule are rationally screened via high-throughput DFT simulation and experimental verification, which act as efficient surface passivation agents to heal the lead- and iodine-related defects. As a result, the defect-less perovskite films deliver encouraging device power conversion efficiency >24% with negligible hysteresis. A remarkable open-circuit voltage (Voc) of 1.17 V was obtained with a Voc deficit of 370 mV, featuring the outstanding defect-passivation capability of the SIP strategy. Moreover, the SIP-treated devices show exceptional ambient stability and maintain 70% of the initial efficiency after 150 h of high humidity exposure (relative humidity 70%-80%). Our results highlight the importance of the rational design of passivation agents to realize high-performance perovskite electronics.

Ion Diffusion Management Enables All-Interface Defect Passivation of Perovskite Solar Cells.

Perovskite solar cells (PSCs) have demonstrated over 25% power conversion efficiency (PCE) via efficient surface passivation. Unfortunately, state-of-the-art perovskite post-treatment strategies can solely heal the top interface defects. Herein, we propose an ion diffusion management strategy to concurrently modulate the top interfaces, buried interfaces, and bulk interfaces (i.e., grain boundaries) of perovskite film, enabling all-interface defect passivation. Specifically, this method is enabled by applying double interactive salts of octylammonium iodide (OAI) and guanidinium chloride (GACl) onto the three-dimensional (3D) perovskite surface. We reveal that the hydrogen-bonding interaction between OA+ and GA+ decelerates the OA+ diffusion and therefore forms dimensionally broadened 2D capping layer. Additionally, the diffusion of GA+ and Cl- determines the composition of the bulk and buried interface of PSCs. As a result, we can obtain n-inter-i-inter-p, i.e., 5-layer structured PSCs with a champion PCE of 25.43% (certified 24.4%). This approach also enables the substantially improved operational stability of perovskite solar cells. This article is protected by copyright. All rights reserved.

Regularly arranged ZnO/TiO2, HfO2, and ZrO2 core/shell hybrid nanostructures - towards selection of the optimal shell material for efficient ZnO-based UV light emitters

Luminescent properties of ZnO/TiO2, ZnO/HfO2, and ZnO/ZrO2 core/shell hybrid nanotubes (NTs) with the shell thickness varying between 9 and 40 nm were studied. The hybrid nano-ceramics demonstrated distinct differences in their luminescence performance. The highest UV/VIS ratio and the longest fluorescence lifetime were observed for the ZnO/TiO2 NTs. The behavior was ascribed to resonance energy/charge transfer between TiO2 and ZnO owing to the similar position of conduction and valence band edges, and comparable bandgap energies (Eg) which allowed for a simultaneous excitation of electron-hole pairs in both semiconductors. The difference between the other two core/shell NTs was attributed to the larger bond energy of HfO2 as compared to that of ZrO2 and smaller refractive index of HfO2 as compared to that of ZnO. The results obtained in this work strongly indicate that in the optimal core/shell heterostructure, not only the shell material should form a type-I heterojunction with the ZnO nanostructure but also the excitation energy should be comparable to or larger than the Eg of the coating material. Moreover, the shell material with a high negative formation enthalpy and lower refractive index than that of ZnO would assure an efficient surface passivation and better photon extraction from the emitter.

Paper-Thin Al-Catalyzed Si Nanowire Solar Cells and Efficiency Enhancement by Hybrid Nanostructures with Mn-Doped Perovskite Nanocrystals

The use of thin silicon (Si) wafers and streamlined fabrication methods that can be scaled up without compromising device efficiency is a key strategy for realizing low-cost and flexible solar cells. Herein, aluminum (Al)-catalyzed Si nanowires (NWs) formed by vapor–liquid–solid growth on paper-thin polished and etched Si(111) wafers of 100 and 60 μm thickness with high proficiency for minimizing interfacial defects and light absorption loss have been accomplished. Successfully addressing the major challenge of rapid Al catalyst oxidation by ex situ and uncomplicated growth conditions allows for the potential to scale up the process while preventing the formation of deep-level traps resulting from catalyst contamination. The Si NWs formed on the nanowave surface of a thin etched Si wafer evidence comparable light absorbance and low interfacial defects to those grown on thin polished and traditional Si wafers. Fabrication of thin Si NW solar cells with a homojunction p+–p–n–n+ structure toward the enhanced power conversion efficiency (PCE) by hybrid nanostructures with manganese-doped cesium lead chloride (CsPb0.81Mn0.19Cl3) perovskite nanocrystals (NCs) using a simple drop-casting method has been explicitly explained. The precise tuning of the energy band and NC size enabled a significant radiative energy transfer by matching the light absorption range of NCs with a high Stokes shift in the luminescence spectrum and the spectral response range of underlying Si solar cells. The nonradiative energy transfer efficiency of NCs and an NC amount infiltration on homojunction Si NW solar cells for maximizing PCE enhancement were examined. The effective photon-harvesting architectures of NWs and NCs together with efficient energy transfers and surface passivation from NCs to the underlying homojunction Si NW solar cells could capably enhance PCE up to a 9% level. These results exhibited the potential for feasible low-cost and large-scale fabrication techniques with lower consumption of raw materials for future photovoltaic applications.

Efficient surface passivation of germanium nanostructures with 1% reflectance

Germanium (Ge) is a vital element for applications that operate in near-infrared wavelengths. Recent progress in developing nanostructured Ge surfaces has resulted in >99% absorption in a wide wavelength range (300–1700 nm), promising unprecedented performance for optoelectronic devices. However, excellent optics alone is not enough for most of the devices (e.g. PIN photodiodes and solar cells) but efficient surface passivation is also essential. In this work, we tackle this challenge by applying extensive surface and interface characterization including transmission electron microscopy and x-ray photoelectron spectroscopy, which reveals the limiting factors for surface recombination velocity (SRV) of the nanostructures. With the help of the obtained results, we develop a surface passivation scheme consisting of atomic-layer-deposited aluminum oxide and sequential chemical treatment. We achieve SRV as low as 30 cm s−1 combined with ∼1% reflectance all the way from ultraviolet to NIR. Finally, we discuss the impact of the achieved results on the performance of Ge-based optoelectronic applications, such as photodetectors and thermophotovoltaic cells.

Highly Efficient and Stable Perovskite Solar Cells Incorporating Chlorinated-Tin Oxide Electron Transport Layers Prepared via Coordination of Diacyl-Metal Cations

The surface passivation of metal oxide electron-transport layers (ETLs) is a powerful strategy for realizing high-performance perovskite solar cells. The surface properties of ETLs strongly influence carrier injection and transfer dynamics; therefore, control of the carrier trap density is crucial. Semiconducting small molecules are considered suitable materials for surface passivation. However, they are expensive and vulnerable to humid atmospheres. Ultrathin polymer layers can have poor surface coverage owing to their spinodal dewetting. In this study, we employ adipoyl chloride as an organic ligand for the chemically robust and efficient surface passivation of SnO2 ETLs. Through the strong coordination of diacyl-metal cations, acyl groups are adsorbed onto the SnO2 surfaces, and the density of oxygen vacancies is significantly reduced. Furthermore, the changing surface properties of the SnO2 ETLs also contribute to the improvement of perovskite morphologies. The deeper energy levels and reduced defect density of the ETLs promote electron injection and transfer at the perovskite and ETL interface. The enlarged perovskite grains are accompanied by improved electron mobility and reduced grain-boundary density. The resulting power conversion efficiency (PCE) increases from 19.36 to 21.41%. The normalized PCE is retained at 90.4% of the initial value for 720 h under 1 sun illumination without the encapsulation of the devices.

Two-dimensional single crystal monoclinic gallium telluride on silicon substrate via transformation of epitaxial hexagonal phase

Van der Waals (vdW) epitaxial growth of large-area and stable two-dimensional (2D) materials of high structural quality on crystalline substrates is crucial for the development of novel device technologies. 2D gallium monochalcogenides with low in-plane symmetry stand out among the layered semiconductor materials family for next-generation optoelectronic and energy conversion applications. Here, we demonstrate the formation of large-area, single crystal and optically active 2D monoclinic gallium telluride (m-GaTe) on silicon substrate via rapid thermal annealing induced phase transformation of vdW epitaxial metastable hexagonal gallium telluride (h-GaTe). Stabilization of multilayer h-GaTe on Si occurs due to the role of the first layer symmetry together with efficient GaTe surface passivation. Moreover, we show that the phase transformation of h-GaTe to m-GaTe is accompanied by the strain relaxation between Si substrate and GaTe. This work opens the way to the fabrication of single-crystal 2D anisotropic semiconductors on standard crystalline wafers that are difficult to be obtained by epitaxial methods.

Enhanced performance of planar perovskite solar cells by doping the SnO2 electron transport layer with guanidinium chloride

Tin (IV) oxide is a highly promising electron transport layer (ETL) for lead halide perovskite solar cells due to its high conductivity, transparency, wide band gap, and the possibility of low-temperature processing. Nonetheless, charge carrier recombination processes at the SnO2/perovskite interface diminish the device performance. Here, we demonstrate that SnO2 doping with guanidine hydrochloride (G-SnO2) leads to efficient surface passivation and a larger band offset between the ETL and the perovskite layer, resulting in reduced voltage losses and faster electron transfer. Moreover, G-SnO2 facilitates the growth of highly crystalline perovskite layers. Consequently, a power conversion efficiency of up to 23.48% and a high open-circuit voltage of 1.18 V are obtained in solar cells incorporating the G-SnO2 ETL. These devices also exhibited negligible hysteresis and maintained more than 96% of their initial power conversion efficiency after 1,250 h exposure to the air without encapsulation.

Improved surface passivation of lead sulfide quantum dots using less sterically crowded alkylammonium iodides

Efficient surface passivation of colloidal quantum dots (CQDs) is crucial for improving the photovoltaic performance of CQD-based solar cell (CQDSC) devices. Although several alkylammonium iodides (AMIs), representatively tetra-n-butylammonium iodide (TBAI), have been reported for iodide passivation of lead sulfide (PbS) CQDs, the factors influencing the passivation are still barely understood. In this research, the impacts of steric crowding, acidity and ionic dissociation of seven AMIs with different lengths and numbers of alkyl substituents on the iodide passivation of the PbS CQDs are studied. The oleate ligands on the pristine CQD surface are more effectively exchanged with iodides by less sterically crowded AMIs. The higher acidity of tertiary AMIs compared with quaternary AMIs also enhances the elimination of oleate ligands and the passivation of iodides. The extent of the ligand exchange consequently influences the photovoltaic properties of CQDSCs, including trap density, built-in potential and charge mobility. Thus, the triethylamine hydroiodide (tri-EAHI)-treated CQDSC demonstrates the highest power conversion efficiency of 5.37% for a single CQD layer-based cell and 10.1% for a PbS-tri-EAHI/PbS-PDT-based bilayer cell.

Surface Characterization of the Solution‐Processed Organic–Inorganic Hybrid Perovskite Thin Films

The surface properties of organic-inorganic hybrid perovskites can strongly affect the efficiency and stability of corresponding devices. Even though different surface passivation methods are developed, the microscopic structures of solution-processed perovskite film surfaces are not systematically studied. This study uses low-temperature scanning tunneling microscopy to study the organic-inorganic hybrid perovskite thin films, MA0.4 FA0.6 PbI3 and MAPbI3 , synthesized by the spin-coating method.Flat surface structures, atomic steps, and crystal grain boundaries are resolved at an atomic resolution. The surface imperfections are also characterized, as well as the dominant defects.Simulations on different types of iodine vacancy configurations are performed by density functional theory calculations.In addition, it is observed that the surface iodine lattice structure is unstable during scanning. Tip scanning can also cause the vertical migration of surface iodine ions. The measurements provide the direct visualizations of the surface imperfections of the solution-processed perovskite films. They are essential for understanding the surface-related optoelectronic effects and rationally designing more efficient surface passivation methods.

High-efficiency luminescent solar concentrators based on Composition-tunable Eco-friendly Core/shell quantum dots

Luminescent solar concentrators (LSCs) fabricated using colloidal quantum dots (QDs) are considered as promising cost-effective solar collectors for future building-integrated photovoltaics (BIPV). Nevertheless, the solar-to-electricity conversion efficiency of the LSCs is commonly low due to limited quantum efficiency and large reabsorption loss of QDs. In addition, most of the efficient LSCs contain heavy metal-based QDs, limiting their potential commercial applications. Herein, we demonstrate a novel type of eco-friendly CuGaAlS/ZnS (CGAS/ZnS) core/shell QDs with efficient surface passivation and manipulated their optical properties by varying the copper contents, which effectively regulates the intrinsic band structure and radiative recombination dynamics. As a result, the optimal Cu-deficient CGAS/ZnS core/shell QDs exhibit the highest photoluminescence quantum yield (PLQY) of ∼ 91 % and large Stokes shift (∼0.81 eV). The prepared QDs were applied as emitters and integrated in polymer matrix to fabricate LSCs (10 × 10 × 0.15 cm3), delivering an unprecedented power conversion efficiency (PCE) of 4.29 % under standard one sun AM 1.5G illumination (100 mW cm−2). Our results imply that tuning the components of multinary environment-friendly core/shell QDs endows the feasibility to realize low-cost and high-efficiency BIPV applications.

Surface Passivation of Layered MoSe2 via van der Waals Stacking of Amorphous Hydrocarbon.

Development of efficient surface passivation methods for semiconductor devices is crucial to counter the degradation in their electrical performance owing to scattering or trapping of carriers in the channels induced by molecular adsorption from the ambient environment. However, conventional dielectric deposition involves the formation of additional interfacial defects associated with broken covalent bonds, resulting in accidental electrostatic doping or enhanced hysteretic behavior. In this study, centimeter-scaled van der Waals passivation of transition metal dichalcogenides (TMDCs) is demonstrated by stacking hydrocarbon (HC) dielectrics onto MoSe2 field-effect transistors (FETs), thereby enhancing the electric performance and stability of the device, accompanied with the suppression of chemical disorder at the HC/TMDCs interface. The stacking of HC onto MoSe2 FETs enhances the carrier mobility of MoSe2 FET by over 50% at the n-branch, and a significant decrease in hysteresis, owing to the screening of molecular adsorption. The electron mobility and hysteresis of the HC/MoSe2 FETs are verified to be nearly intact compared to those of the fabricated HC/MoSe2 FETs after exposure to ambient environment for 3months. Consequently, the proposed design can act as a model for developing advanced nanoelectronics applications based on layered materials for mass production.