Influence of hole mobility on the response characteristics of p-type nickel oxide thin film based glucose biosensor

NiOx Passivation in Perovskite Solar Cells: From Surface Reactivity to Device Performance

Nonstoichiometric nickel oxide (NiOx) is one of the very few metal oxides successfully used as hole extraction layer in p-i-n type perovskite solar cells (PSCs). Its favorable optoelectronic properties and facile large-scale preparation methods are potentially relevant for future commercialization of PSCs, though currently low operational stability of PSCs is reported when a NiOx hole extraction layer is used in direct contact with the perovskite absorber. Poorly understood degradation reactions at this interface are seen as cause for the inferior stability, and a variety of interface passivation approaches have been shown to be effective in improving the overall solar cell performance. To gain a better understanding of the processes happening at this interface, we systematically passivated specific defects on NiOx with three different categories of organic/inorganic compounds. The effects on NiOx and the perovskite (MAPbI3) deposited on top were investigated using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Here, we find that the perovskite's structural stability and film formation can be significantly affected by the passivation treatment of the NiOx surface. In combination with density functional theory (DFT) calculations, a likely origin of NiOx-perovskite degradation interactions is proposed. The surface passivated NiOx layers were incorporated into MAPbI3-based PSCs, and the influence on device performance and operational stability was investigated by current-voltage (J-V) characterization, impedance spectroscopy (IS), and open circuit voltage decay (OCVD) measurements. Interestingly, we find that a superior structural stability due to interface passivation must not relate to high operational stability. The discrepancy comes from the formation of excess ions at the interface, which negatively impacts all solar cell parameters.

Observation of Charge Separation Enhancement in Plasmonic Photocatalysts under Coupling Conditions

Surface plasmon resonance-induced charge separation plays key roles in plasmon-related applications, especially in photocatalysis and photovoltaics. Plasmon coupling nanostructures exhibit extraordinary behaviors in hybrid states, phonon scattering, and ultrafast plasmon dephasing, but plasmon-induced charge separation in these materials remains unknown. Here, we design Schottky-free Au nanoparticle (NP)/NiO/Au nanoparticles-on-a-mirror plasmonic photocatalysts to support plasmon-induced interfacial hole transfer, evidenced by surface photovoltage microscopy at the single-particle level. In particular, we observe a nonlinear increase in charge density and photocatalytic performance with an increase in excitation intensity in plasmonic photocatalysts containing hot spots as a result of varying the geometry. Such charge separation increased the internal quantum efficiency by 14 times at 600 nm in catalytic reactions as compared to that of the Au NP/NiO without a coupling effect. These observations provide an improved understanding of charge transfer management and utilization by geometric engineering and interface electronic structure for plasmonic photocatalysis.

High-Performance Inverted Perovskite Solar Cells with Mesoporous NiO x Hole Transport Layer by Electrochemical Deposition

Perovskite solar cells (PSCs) based on a NiO _x hole transport layer (HTL) with an inverted p-i-n configuration have yielded highly efficient and relatively stable devices. Here, we develop a simple electrochemical deposition method for quickly and evenly preparing a mesoporous NiO _x film. It is demonstrated that the increasing thickness and decreasing surface roughness of the NiO _x film are beneficial for light transmission. The optimal condition for preparing NiO _x films is achieved by adjusting the deposition time at a certain applied current density, which exhibits excellent optical transmittance and suitable thickness and band gap, thus reducing optical loss and enhancing hole extraction at the interface between HTL and the perovskite layer and therefore improving photovoltaic performances. The finite-difference time-domain simulation confirms the optimal thickness of the NiO _x layer and coincides with our experiment results. An optimal power conversion efficiency (PCE) of 17.77% with an active area of 0.25 cm² is achieved. The prepared device shows negligible hysteresis, high reproducibility, and high uniformity with a PCE difference of 2% for measuring the different sites from edge to center. This simple fabrication process paves a novel way to the evolution of PSCs based on NiO _x and rapid commercialization.

Enzymatic electrochemical biosensor for urea with a polyaniline grafted conducting hydrogel composite modified electrode

A new conducting polymer hydrogel (CPH) comprising polyaniline grafted polyvinyl alcohol–polyacrylamide ensured high enzyme loading and urea sensitivity.

Reagentless uric acid biosensor based on Ni microdiscs-loaded NiO thin film matrix

The development of a noninvasive test for uric acid has been the holy grail of uric acid detection research over the last decade. In the present work, a novel matrix comprising of a NiO thin film (a biocompatible material) loaded with Ni microdiscs was prepared on an ITO-coated glass substrate (Ni/NiO/ITO) with the help of RF sputtering for the reagentless detection of uric acid. The bioelectrode was fabricated by immobilizing uricase using a physical adsorption technique on the surface of the Ni/NiO/ITO electrode. The prepared matrix was found to be efficient in sensing biological processes occurring on the surface of the bioelectrode (Ur/Ni/NiO/ITO) in the presence of the analyte (uric acid) to obtain an electronic output. The biosensor exhibits a high sensitivity (431.09 μA mM(-1)), low Km value (0.15 mM), high apparent enzyme activity (5.07 × 10(-2) units per cm(2)), high shelf life (20 weeks) and good selectivity for the detection of uric acid over a wide concentration range (0.05 mM to 1 mM) without any external mediator in the PBS buffer. The obtained results are encouraging for the realization of a reagentless uric acid biosensor with efficient sensing response characteristics.

A highly efficient urea detection using flower-like zinc oxide nanostructures

A novel matrix based on flower-like zinc oxide nanostructures (ZnONF) has been fabricated using hydrothermal method and exploited successfully for the development of urea biosensor. Urease (Urs) is physically immobilized onto the ZnO nanostructure matrix synthesized over platinized silicon substrate. The surface morphology and crystallographic structure of the as-grown ZnONF have been characterized using a scanning electron microscope (SEM) and X-ray diffraction (XRD) techniques. The fabricated amperometric biosensor (Urs/ZnONF/Pt/Ti/Si) exhibits a linear sensing response towards urea over the concentration range 1.65 mM to 16.50mM with an enhanced sensitivity (~132 μA/mM/cm(2)) and a fast response time of 4s. The relatively low value of Michaelis-Menten constant (Km) of 0.19 mM confirms the high affinity of the immobilized urease on the nanostructured ZnONF surface towards its analyte (urea). The obtained results demonstrate that flower-like ZnO nanostructures serve as a promising matrix for the realization of efficient amperometric urea biosensor with enhanced response characteristics.

First-principles assessment of hole transport in pure and Li-doped NiO

Hole transport in nickel oxide and Li_0.125Ni_0.875O is predicted to be anisotropic. Homogeneous alloying at a high enough concentration introduces free holes, making Li_0.125Ni_0.875O a promising p-type hole conductor.

All solution-processed inorganic/organic hybrid permeable metal-base transistor

All solution-processed inorganic/organic hybrid permeable-base transistor (PMBT) based on nickel oxide emitter and P3HT collector is developed. Due to the high charge injection properties of nickel oxide and spontaneously formed nano-pinholes in the base electrode, the devices exhibit high common-base and common-emitter current gains up to 0.98 and 304, respectively with saturated output current.

Valence band-edge engineering of nickel oxide nanoparticles via cobalt doping for application in p-type dye-sensitized solar cells

We have systematically studied the effects of substitutional doping of p-type nanoparticulate NiO with cobalt ions. Thin films of pure and Co-doped NiO nanoparticles with nominal compositions Co(x)Ni(1-x)O(y) (0 ≤ x ≤ 0.1) were fabricated using sol-gel method. X-ray photoelectron spectroscopy revealed a surface enrichment of divalent cobalt ions in the Co(x)Ni(1-x)O(y) nanoparticles. Mott-Schottky analysis in aqueous solutions was used to determine the space charge capacitance values of the films against aqueous electrolytes, which yielded acceptor state densities (N(A)) and apparent flat-band potentials (E(fb)). Both N(A) and E(fb) values of the doped NiO were found to gradually increase with increasing amount of doping; thus the Fermi energy level of the charge carriers decreased with Co-doping. The photovoltage of p-DSCs constructed using the Co(x)Ni(1-x)O(y) films increased with increasing amount of cobalt, as expected from the trend in the E(fb). Co-doping increased both carrier lifetimes within the p-DSCs and the carrier transport times within the nanoparticulate semiconductor network. The nominal composition of Co₀.₀₆Ni₀.₉₄O(y) was found to be optimal for use in p-DSCs.