Transient Photocurrent Measurements Research Articles

Stable Radical Isoporphyrin Copolymer Prepared with Di(phenylphosphane).

Two diphosphanes with variable-length ligands tested as nucleophiles to prepare isoporphyrin copolymers in the presence of ditolylporphyrin of zinc (ZnT2P) prevented the oxidation of the diphosphine ligand. This paper demonstrates the power of this approach and describes the photoelectrocatalytic properties. The obtained copolymers were characterized by UV-vis spectroscopy, X-ray photoelectron spectroscopy, atomic force micrograph (AFM), EQCM (Electrochemical Quartz Cristal Microbalance) and electrochemistry. Their impedance properties (EIS) were studied and their photovoltaic performances were also investigated by photocurrent transient measurements under visible light irradiation.

Photoelectrical performances of semiconductor-based devices having CoFe and CoFeNi magnetic interlayers

This study was designed to examine the photoelectric device performances of cobalt-iron (CoFe) and cobalt-iron-nickel (CoFeNi) materials with good magnetic properties, specifically to investigate the effect of the Ni element on the electrical properties. In this context, Al/CoFe/p-Si and Al/CoFeNi/p-Si devices were produced by coating both materials between the semiconductor and the metal using the radio frequency (RF) sputtering method. First of all, to investigate the structural properties of the coated films, the content analysis was carried out by x-ray diffraction (XRD) analysis. To determine the photoelectrical properties of the produced devices, current–voltage and transient photocurrent measurements were performed and analyzed under different light intensities. While the ideality factor (barrier height) values of the devices produced using CoFe and CoFeNi materials were found to be 11.45 (0.487 eV) and 9.86 (0.513 eV), respectively, in the dark, they were obtained as 13.29 (0.446 eV) and 11.02 (0.484 eV) under 100 mW cm−2 illumination. It was determined that both devices are sensitive to light, with the sensitivity of the device with the CoFeNi interlayer being much higher. In addition, photocapacitance and photoconductivity measurements were carried out to examine the photocapacitor performance of the devices. As a result of the investigations, both current–voltage, photocurrent, and photo-capacitance/conductivity measurements showed that the device with the CoFeNi interface layer showed better performance than the device with the CoFe interface. Therefore, it has been determined that the Ni element has a positive effect on electrical properties. The results obtained show that the prepared materials and produced devices can be used in photovoltaic applications.

Synthesis of a novel biomass waste-based photocatalyst for degradation of high concentration organic pollutants under visible light: Optimization of synthesis condition and operational parameters via RSM-CCD

Reducing electron-hole pair recombination rate under visible light and preventing α-Fe2O3/WO3 nanoparticle aggregation enhances the photocatalytic efficiency. Herein, a novel heterojunction-activated carbon-based photocatalyst (α-Fe2O3/WO3/AC) was successfully synthesized from Rosa Canina seeds and characterized by PL, EIS, Photocurrent, ESR, XPS, LC-MS, FTIR, XRD, SEM, EDS-map, TEM, and BET analyses. Investigating the influence of significant parameters, including impregnation ratio (1–5), activation temperature (400–600 °C), and α-Fe2O3/WO3 loading (10–90 wt.%) by RSM method resulted in optimal photocatalyst synthesis (50 wt.%: FeW/AC3–500) evidenced by its capability for doxycycline degradation. The maximum doxycycline degradation (98.01 %) was achieved under optimal conditions with a degradation rate constant of 0.03 min−1. Trapping experiments revealed that •OH and •O2− played crucial roles in photocatalysis. The possible doxycycline degradation pathway of (50 wt.%: FeW/AC3–500) photocatalyst is proposed. Based on the transient photocurrent measurements and EIS results, the 50 wt.% FeW/AC3–500 composite exhibited a significant enhancement in photocatalytic activity, which can be attributed to the efficient speed of electron-hole separation. Overall, an innovative approach was introduced to design an efficient AC-based photocatalytic process, which enhances the performance of wastewater treatment and environmental remediation.

MR-TADF emitter as a dual-functional solid additive to extend exciton lifetime and optimize morphology for organic solar cells with ∼19% efficiency

Extending exciton lifetime and optimizing active-layer morphology simultaneously to advance power conversion efficiency (PCE) of organic solar cells (OSCs) still encounter great challenges by conventional additive strategies. Herein, to address these issues, a multiple-resonance thermally activated delayed fluorescence (MR-TADF) emitter of BNS-H1 containing heteroatom-embedded polycyclic aromatic hydrocarbon is innovatively served as a dual-functional solid additive (DFSA) in OSCs. The primary studies on the PM6:Y6 system indicate that BNS-H1 plays an exceptional dual-functional role in promoting π-π stacking of Y6 component and optimizing active-layer morphology. Meanwhile, the steady/transient photoluminescence spectra and transient photocurrent measurements further reveal that incorporating BNS-H1 with the system enhances emission of PM6 component, extend exciton lifetime and diffusion distance. Consequently, four types of binary OSCs demonstrate a notable improvement in PCE processed by 1.0 wt% BNS-H1. Specifically, the BNS-H1-treated OSCs with PM6:Y6 and PM6:BTP-eC9 systems achieve outstandingly increasing PCEs of 17.4% and 18.8% compared to their BNS-H1-free control devices, respectively. Furthermore, device stability of the BNS-H1-treated PM6:Y6 devices is significantly enhanced. Notably, the approaching 19% efficiency is one of the highest PCEs in the reported non-volatile additives treated binary OSCs. Our work highlights the significant potential of MR-TADF emitter as a DFSA in OSCs for boosting PCEs.

Enhanced organic pollutant and AOX degradation of lignin-biochar/ZnAl2O4/BiPO4 with adsorption-photocatalysis synergy: Roles of lignin-biochar

In this work, lignin-biochar (LC)/ZnAl2O4/BiPO4 with adsorption and photocatalysis synergy were fabricated through hydrothermal process. The roles of lignin-biochar on the crystalline structure, shape and photoelectrochemical capacities of LC/ZnAl2O4/BiPO4 were carried out by X-ray power diffractometer pattern (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffusion reflectance spectra (UV–Vis DRS), photoluminescence spectra (PL), transmission electron microscope (TEM), scanning electron microscope (SEM), electrochemical impedance and transient photocurrent measurements. Photocatalytic experiment showed that the adsorption and photocatalytic efficiencies of ZnAl2O4/BiPO4 were greatly boosted with the introduced lignin-biochar, which is owing to its higher surface specific area, larger aromatic ring structure and superior electron transmission capacity. The highest kinetic constant of LC/ZnAl2O4/BiPO4 on the MB degradation is 2.1342 h−1 under UV illumination, increased by 5.52-fold for BiPO4 and 2.23-fold for ZnAl2O4/BiPO4, respectively. Meanwhile, the LC/ZnAl2O4/BiPO4 composites display excellent performance in the bamboo pulp bleaching wastewater treatment, and the CODCr and AOX removals of the wastewater are 65.2 % and 69.2 %, respectively. The lignin-biochar in the composites can not only enhance the adsorption of pollutant in the wastewater, but accept the photo-generated electrons from the semiconductor, leading to an enrichment of the pollutant and accelerated separation of electrons-holes pairs, ultimately enhancing the photocatalytic activities. The superior adsorption and photocatalytic efficiency of lignin-biochar-based composite makes it a promising candidate for the elimination of refractory pollutant in the industrial wastewater.

Charge Carrier Trapping in the Surface Region of BiVO4 Photoanodes

Photoelectrochemical water splitting is a promising method for converting solar energy into chemical energy stored in molecular hydrogen and oxygen. However, the efficiency of this process is heavily dependent on the properties of the photoelectrode materials used. Metal oxide semiconductors, such as BiVO4, are commonly used as photoanode materials, but they have poor charge transport properties and surface catalytic activity, which can limit their efficiency.To address these limitations, catalysts are often incorporated onto the surface of the photoanode to improve its surface activity. However, the overall efficiency of the photoelectrochemical process is also influenced by charged defect sites present both in the bulk and on the surface of the semiconductor. These defect sites can trap charges and hamper the kinetics of the process in the millisecond time scale. To address this issue, covalently coordinated catalyst layers and surface doping can be used to eliminate these trapped charges. Moreover, the bulk charge carriers are not entirely decoupled from the surface processes and can be influenced by surface treatments. Therefore, a multi-folded approach that considers both the surface and bulk properties of the photoanode, as well as the role of the catalysts, is necessary to improve the overall efficiency of photoelectrochemical water splitting.We have investigated interfacial charge trapping and transfer processes through a CoOx catalyst layer deposited on BiVO4 by atomic layer deposition (ALD) and cobalt incorporated into the subsurface region. We have shown, by the combination of activity studies and spectroscopy investigations, that oxygen vacancies modified by cobalt incorporation have a remarkable impact on the water oxidation activity and charge injection efficiency. We further demonstrated by transient photocurrent measurements performed by fast LED light pulses (within ms time scale) that the CoOx catalyst layer reduced the number of trapped electrons and improved the rate of charge utilization. Cobalt ions in the subsurface region on the other did not act as catalytic centers but they eliminated the trapping process. We have also confirmed these observations by transient absorption spectroscopy investigations and showed that cobalt incorporation had a much bigger effect on the charge recombination lifetime.

Popcorn-stick-like NH2-UiO-66/TiO2 nanotube nanocomposites toward optimized photocatalytic carbon oxidation with nitrogen dioxide

Developing photocatalytic technologies for pollutants removal with high harmless product selectivity is a significant challenge. Construction and optimization of nanocomposites junction with appropriate band alignments is an effective method for achieving this objective. Herein, a unique popcorn-stick-like NH2-UiO-66/TiO2 nanotube nanocomposites with staggered band alignment is fabricated. The small metal organic frameworks (MOFs) particles with diameters around 20 nm are uniformly dispersed on the surface of TiO2 nanoplates, creating a popcorn-stick-like structure. The resulting as-synthesized nanocomposites photocatalysts show distinguished photocatalytic activity for simultaneous removal of carbon particles and nitrogen dioxide with 100% NO2 conversion and 99% N2 selectivity, about 3.9 times higher than that of pristine TiO2. The significant enhancement is attributed to the rapid charge separation and transfer in TiO2 and NH2-UiO-66 interface and the visible light absorption. The enhanced charge transfer follows double charge transfer mechanism, which is confirmed by surface photovoltage spectroscopy, photoluminescence, transient photocurrent measurements, and electrochemical impedance spectroscopy. This study demonstrates the potential for the simultaneously removal of two pollutants using the composite of TiO2 and MOF materials with high surface area and visible light absorption ability, thereby providing the possible applications of NH2-UiO-66/TiO2 composites in environmental remediation including air purification and wastewater treatment.

Facile synthesis of silver doped WO3 nanocomposite with 2-D reduced graphene oxide to boost photocatalytic efficiency

Two-dimensional (2D) carbonaceous substances and their nanohybrid have lately garnered great interest as photocatalysts owing to outstanding contribution toward photocatalytic degradation and purification. A novel 2-D rGO dependent Ag/WO3 photocatalyst was successfully fabricated using hydrothermal and ultrasonic synthesis processes. The photocatalysts properties such as surface, structure, morphology and optical were studied using modern analytical techniques. The photocatalytic effectiveness of the synthesized product was evaluated by measuring the rate of Methylene blue (MB) dye mineralization when exposed to a visible source. By virtue of its lower charge transfer resistance (Rct; 0.6 Ω) and better electrical conductivity, the photocatalyst demonstrated much stronger photocatalytic behavior toward dye removal than pure tungsten trioxide and silver doped WO3 photocatalysts. The Ag/WO3/rGO photocatalyst degraded the dye at a rate of almost 96.92% faster than Ag/WO3 (0.011 min−1) and WO3 (0.009 min−1). The separation of photogenerated electron (e-) and hole (h+) pairs and the rise in optical absorbance contributed to a notable improvement in WO3′s photocatalytic efficiency after adding silver dopant and rGO sheets. Transient photocurrent measurements revealed that the graphene-based material has persistent photo-excited charge carriers.

Modelling TiO2 photoanodes for PEC water splitting: Decoupling the influence of intrinsic material properties and film thickness

Semiconductor metal oxides are intensively studied in electrodes for photoelectrochemical (PEC) water splitting. On a series of nanoparticulate TiO2 photoanodes, we analyze specific fabrication variables by means of data fitting. First, the experimental outcome is gathered using PEC characterization techniques, mostly cyclic voltammetry and transient photocurrent measurements. Subsequently, we apply models to gain insights into the involved charge trapping and transfer phenomena. We find that capacitance coefficients and the switch-on transient kinetics depend on the TiO2 layer thickness, respectively indicating surface mechanisms and stationary regimes that are mediated by light accessibility. On the contrary, exponential factors of capacitance are independent of thickness, but reflect changes in the density of electron states with different sintering atmospheres. Also, the transfer resistance in the electrolyte side is indirectly influenced by sintering. Through meticulous quantitative analysis of trends, we stablish simple mathematical relationships that connect thickness-dependent parameters. This knowledge delves into fundamental mechanisms governing the TiO2 photoelectrode behaviour, and aims to facilitate further improvements in the efficiency of materials and electrodes for green hydrogen production.

Picosecond trion photocurrent dynamics in FAPbI3 quantum dot films

Nanocrystal quantum dot (QD) films have been highlighted as unique building blocks of optoelectronic devices due to their unique properties based on electronic interactions among close-packed QDs. Although the creation and annihilation processes of trions play important roles in optical responses of isolated QDs, their contributions to photocurrent conversion processes in QD films are unclear. Here, we studied trion dynamics in QD films by transient photocurrent measurements. We observed that the transient photocurrent signal has two decay components: a fast trion component with a lifetime shorter than 1 ns and a slow exciton component with several tens of nanoseconds. Moreover, we control the signal amplitude of the fast trion decay component by tuning extra charge doping to QDs. These results demonstrate the control of optoelectronic responses of QD films via bias electric voltage and will pave the way for QD-based ultrafast optoelectronics.

Synthesis of doped and porous CuO with boosted light-harvesting features for the photocatalytic mineralization of azo dyes

Porous Ni-doped copper oxide (NCO) photocatalyst has been produced using chemical activation and metal doping techniques. Structural, optical, morphological, and electrical analyses were performed on copper oxide (CO) and porous NCO photocatalysts. The monoclinic-phased, UV/Vis light-triggered, electrically conductive, and porous-surfaced NCO photocatalyst was successfully synthesized, according to a detailed physicochemical investigation. The photo-decomposition abilities of synthetic porous NCO and counterpart CO photocatalysts were investigated and compared using Allura red (AR). According to the photocatalytic study, the porous NCO photocatalyst outperformed its counterpart (CuO) and eliminated 91.4% (adsorption: 18%; decomposition: 79%) of the AR dye in 48 min. Over the porous NCO photocatalyst, the AR dye disintegrated at a rate of 0.024 min−1, which is more than 1.84 times quicker than the rate of disintegration over the CO photocatalyst. The porous NCO photocatalyst, as synthesized, preserved 88% of its photocatalytic activity after five recyclability tests and had remarkable electron-hole separation activity, according to reusability tests and transient-photocurrent measurements. Also, the radical capture experiment suggested that superoxide and hydroxyl are important for porous NCO's photocatalytic activity. According to the findings of this research, the synthesis of ferromagnetic metal-doped and porous semiconductive materials has a great potential for azo dye breakdown, which makes it an efficient, cost-effective, and environmentally acceptable solution for the clean-up of polluted water.

ZIF-8 derived carbon/g-C3N4 – an all-carbon heterojunction for effective photo-decontamination of Cr(VI) from water

Carbon-based heterojunctions, because of their low toxicity and non-polluting properties, are considered as metal-free alternatives to the traditional metal oxide semiconductors for energy and environmental applications especially in acidic conditions. In this work, an all-carbon heterojunction using exfoliated graphitic carbon nitride (GCN) and porous carbon derived from zeolitic imidazolate framework (CZ8) is developed for chromium (VI) decontamination. The enhanced charge-transfer in the GCN:CZ8 heterojunctions, due to the suppressed electron-hole pair recombination, is evidenced from photoluminescence (PL) spectroscopy, transient photocurrent (TP) measurements and electrochemical impedance spectroscopy (EIS). This phenomenon significantly contributes towards improving the photo-induced decontamination of the noxious Cr(VI). Moreover, the band gap of the optimized GCN:CZ8 heterojunction is 2.48 eV which is relatively narrow than that of the GCN (2.79 eV). Nearly 100 % removal is achieved with the as-synthesized GCN:CZ8 heterojunction even with chromium solution of 100 ppm concentration. The X-Ray photoelectron spectroscopy (XPS) results suggest the facile reduction of Cr(VI) to Cr(III) under the influence of incident photons, and most importantly, the performance efficiency of the heterojunction is maintained ∼100 % up to five continuous cycles. Herein, the optimized GCN:CZ8 heterojunction is established as a potential material towards efficient decontamination of Cr(VI) from water.

Preparation of Two-Dimensional Layered CeO2/Bi2O3 Composites for Efficient Photocatalytic Desulfurization

A two-dimensional layered CeO2/Bi2O3 composite was synthesized by microwave solvothermal method. X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), UV-Vis diffuse reflection spectroscopy (DRS), and X-ray photoelectron spectroscopy (XPS) were used to studied crystal structure, morphology, optical performance, elemental composition and the surface electronic state of the samples. The photocatalytic properties of the prepared samples were evaluated by photocatalytic desulfurization under visible light. When the molar ratio of Ce and Bi was 1:2, CeO2/Bi2O3 composite presented the highest photocatalytic desulfurization rate. Transient Photocurrent measurement, electrochemical impedance spectroscopy (EIS) and photoluminescence spectroscopy (PL) showed that CeO2 and Bi2O3 formed a heterojunction, which could promote the separation of photogenerated electrons and holes, improving the photocatalytic activity. Furthermore, it was found that the active species of hydroxyl radical (·OH) played an important role in the photocatalytic degradation of dibenzothiophene (DBT) based on the active species capture experiment. Finally, a plausible mechanism for the photocatalytic oxidative desulfurization of this nanocomposite was proposed.

Enhanced visible-light-driven heterogeneous photocatalytic CO2 methanation using a Cu2O@Cu-MOF-74 thin film

• Cu 2 O@Cu-MOF-74 core-shell photocatalyst nanocomposite. • Charge transport of photoinduced charge carriers. • Photocatalytic CO 2 reduction under visible light. • Surface coating of a metal-organic framework produced via topotactic conversion. Cuprous oxide is a potential photocatalyst for the reduction of CO 2 . However, its high rate of charge recombination and low ability to adsorb CO 2 limit its activity, particularly when gaseous CO 2 was used. Herein, a Cu-based metal-organic framework (Cu-MOF-74) with high CO 2 adsorption is coated onto Cu 2 O nanowires by a topotactic transformation method. The optimized Cu 2 O@Cu-MOF-74 composite thin film showed a CH 4 evolution rate 4.5 times higher than that of bare Cu 2 O under visible light illumination (>420 nm), with water vapor as the electron donor. Analysis results of electrochemical impedance spectroscopy, transient photocurrent measurements, and fluorescence spectroscopy collectively suggest that the decoration of Cu 2 O with Cu-MOF-74 facilitates electron extraction from excited Cu 2 O, thereby inducing long-lived photocharges for the reduction of CO 2 . This study provides insights into the modification of transition metal oxides for application in photocatalysis by coating the surface with metal-organic frameworks.

Thermal annealing effects on graphene/n-Si Schottky junction solar cell: removal of PMMA residues

Thermal annealing is one of the most effective ways to improve the efficiency of a graphene/n-Si Schottky junction solar cell. Here, its underlying mechanism has been investigated by comparative studies in terms of the removal of polymethyl methacrylate (PMMA) residues, using the J–V characteristics and transient photocurrent and photovoltage measurements. The obtained results have revealed that there are trap states that originate from the PMMA residues and cause the large photocurrent leakage as the intensity of the incident light increases. It is also found that the PMMA residues accelerate deterioration and rapidly invalidate hole doping effects. Such undesirable PMMA residues were effectively removed by the thermal annealing treatments, serving to reduce the photocurrent leakage and increase the stability.

Nanostructured Ruddlesden–Popper-Layered Lead Bromide Perovskites with Stable and Selected Wavelength for Photodetection Applications

Success in photovoltaic power generation has raised a huge possibility in metal halide perovskites to exhibit excellent photodetection performance with the same physics of photocarrier generation, and their collection at terminal electrodes is employable with less defect-assisted carrier recombination loss. To test this, nanostructured Ruddlesden–Popper (RP)-layered perovskite series were synthesized based on a cyclic organic moiety and Br– halide, resulting in (CH)2(MA)n−1PbnBr3n+1 [where CH─2-(1-cyclohexenyl) ethylamine, MA─methylammonium, Br─bromine, and n = 1–4], to explore how best its mono-to-few layer (n) 2D and quasi 2D-structures can offer photodetection performance with maximum absorbance in the unexplored blue-to-green band gap RP perovskites with maximum stability. Thermogravimetric analysis revealed that the very stable nature of these RP perovskites is accompanied by a linear rise in the structural phase transition temperatures, which range from 270 °C (CH)2PbBr4 (n = 1) to 304 °C (CH)2(MA)3Pb4Br13. The RP perovskites (CH)2(MA)n−1PbnBr3n+1 (n = 1–4) demonstrated sharp exciton emission peaks from blue (∼408 nm) to green (∼528 nm). The X-ray diffraction results confirmed the highly crystalline nature of quasi-2D perovskite thin films. Layer-dependent photoluminescence studies exhibit strong room-temperature exciton photoluminescence and high carrier lifetime. The transient photocurrent measurements for (CH)2(MA)3Pb4Br13 (n = 4) RP perovskite thin films show nearly six times the bias voltage changed from 1 to 5 V at 405 nm laser light excitation. In addition, with respect to performance, the (CH)2(MA)3Pb4Br13 photodetector has shown the highest responsivity (67.2 mA/W), ultrafast transient photocurrent response (122 nA), and high EQE (20.6%) as compared to (CH)2(MA)2Pb3Br10 (n = 3) and (CH)2(MA)Pb2Br7 (n = 2) in ambient temperature.

Spike Current Induction by Photogenerated Charge Accumulation at the Surface Sites of Porous Porphyrinic Zirconium Metal-Organic Framework Electrodes in Photoelectrochemical Cells

Abstract Photoelectrochemical (PEC) capacitors have recently garnered increasing interest based on their charge accumulation and dissipation mechanisms, particularly with respect to spike and overshoot currents, and have therefore been investigated for biomedical applications, including nerve photostimulation and biomolecular sensing. Porous metal-organic frameworks (MOFs) are capable of accumulating large amounts of photogenerated charge at their surface sites, owing to their large surface areas, and therefore may have potential as a new material for use in PEC capacitors. To explore the PEC capacitor properties of MOFs, we performed transient photocurrent measurements using PEC cells comprising porphyrinic zirconium MOF (PZ-MOF) electrodes in a phosphate-buffered saline solution. We observed a clear growth and decay of the cathodic current during light irradiation and the generation of an anodic reverse current when the light was turned off, thus inducing spike and overshoot currents. However, no spike or overshoot currents were observed when excess oxygen was introduced into the electrolyte. These results indicate that PZ-MOFs have the ability for photogenerated charge accumulation at the surface pores near the interface between the PZ-MOF electrode and the electrolyte. Thus, we have confirmed that PZ-MOFs are a promising PEC capacitor material that may be used in future biomedical applications.

Accessing Deep Traps Distribution in FeS2‐Doped Organic Photovoltaics

Although doping has the potential to improve the performance of organic photovoltaic cells (OPVc), doping effects on charge transport, recombination, and energetic disorder are still obscure. Doping has two opposing effects: on the one hand, dopant ions create more trap centers, while free dopant‐induced charges fill deep states, potentially providing better performance. The optimum amount of dopants can considerably improve the performance of OPVc. Herein, the energetic distribution of trap states in P3HT: PC71BM‐based OPVc doped with iron pyrite nanocubes (NCs) is reported. Using the reverse bias transient photocurrent (TPC) measurement, the energetic trap distributions with different doping conditions are studied. The photovoltaic characteristics and TPC phenomena of the OPVc greatly improve through doping. Variations in trap distributions with doping levels are analyzed to interpret the obtained trap density of states profiles. The light‐dependent current–voltage characteristics help to identify the presence of a less trap‐assisted recombination process in the optimum device. This study highlights the mechanism for performance improvement in devices with optimal doping of iron pyrite NCs.

Facile and Effective Band Gap Engineering of 2D Ruddlesden–Popper Perovskites with Improved Structural and Optoelectronic Properties

Incorporation of alkali metal ions (Li+, Na+, K+, Rb+, and Cs+) into 3D metal-halide perovskite crystal structures has resulted in improved crystallinity and film morphology, reduced trap density, and enhanced charge carrier transport. However, due to intrinsic structural instability associated with 3D perovskites, their alkali metal ion-doped semiconductors are not a suitable option for real device optoelectronics. In recent years, Ruddlesden–Popper (RP)-phase quasi-two-dimensional (2D) metal halide perovskites have drawn considerable attention due to their tunable energy band gap, large electron and hole diffusion lengths (∼10 μm), and lower recombination rates compared to pristine 2D metal halide perovskites (n = 1). However, alkali metal ion-incorporated RP perovskite systems are not explored much; therefore, we demonstrate the incorporation of Rb+, using the RbI precursor, into the quasi-2D RP perovskite (BA)2(MA)Pb2Br7 (BA = C4H9NH3; MA = CH3NH3), which has also resulted in the successive replacement of Br– with I– in the PbBr6 network. Subsequent replacement of Br– with I– finely tuned the energy band gap from 2.92 to 2.43 eV, while keeping the phase of the pristine lead bromide RP perovskite intact, as confirmed by X-ray diffraction investigations. MA+ cations available at the outer edge sites got partially exchanged with Rb ions, which in turn has regulated the perovskite crystal growth, whereas the excess Rb+ alloyed with replaced Br– to form RbBr, which resulted in the formation of thinner grain boundaries and thus showed improved charge transport. Transient photocurrent measurements performed for RbI-doped perovskites (lateral configuration photodetector: fluorine-doped tin oxide (FTO)/RP-perovskite/FTO of channel width ∼150 μm), for 35 cycles under standard Xe-lamp (100 mW/cm2) illumination, have shown strong and fast photocurrent response with large photoresponsivity (3.92 × 10–4 A/W). Comparison of structural, optical, and optoelectronic properties of RbI-doped RP perovskites is carried out with the mixed RP perovskites and has further confirmed that Rb+ incorporation plays an important role in enhancing the crystal growth.

Photoelectrochemical Modelling of Semiconducting Electrodes for Neural Interfacing

Semiconducting electrodes are increasingly utilised for neural interfacing applications, such as neural recording, stimulation, and photomodulation. To characterize the performance of these electrodes, photoelectrochemical analysis is often undertaken in biologically relevant electrolytes. These include electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and for photomodulation applications, photocurrent (PC) measurements. From such measurements, it is possible to deduce key properties of semiconductor surfaces, such as electrochemical impedance and capacitance, as well as mechanisms of charge transfer. To extract these parameters from the experimental data, equivalent electrical circuit modelling is often employed, but usually only for a single technique at a time which often misses key insights about the processes occurring at the electrode-electrolyte interface. Here we present an equivalent circuit model that simultaneously describes the results from CV, EIS, and PC transient measurements. Using semiconducting nitrogen-doped ultrananocrystalline diamond (N-UNCD) electrodes in saline solution, we show that the model describes physical mechanisms that occur at the interface with electrolyte, encompassing the space charge region, the electrical double layer, and the electrolyte. Using the model we are able to optimize parameters relevant for neural interfacing and suggest that this framework may assist in the characterization of other semiconducting electrodes.