Photocurrent Switching Research Articles

High efficiency bifacial quasi-solid-state dye-sensitized solar cell based on CoSe2 nanorod counter electrode

For traditional dye-sensitized solar cells, one method to increase the long-term stability and enhance the power conversion efficiency (PCE) is to explore the use of bifacial and quasi-solid-state cells (BQDSSCs). In the current work, CoSe2 nanorods with lengths of 70–500 nm and widths of 20–60 nm were prepared via a simple hydrothermal method and served as the counter electrode (CE) material. The photovoltaic results of the bifacial cell revealed that the front and rear irradiation PCEs of the CoSe2 CE can reach 8.02% and 4.22%, which are higher than those of Pt CE (7.46% and 4.04%, respectively), by employing a polyvinylidene fluoride quasi-solid-state electrolyte. Moreover, the CoSe2 nanorod CE possess a good light on-off photocurrent response and switching stability in the BQDSSCs device. The excellent efficiency and long-term photovoltaic stability of the CoSe2 CE-based BQDSSCs were derived from the unique one-dimensional nanostructure and superior electrocatalytic properties for the reduction reaction of I3− to I−, as revealed by cyclic voltammetry (CV), Tafel polarization, and electrochemical impedance spectroscopy (EIS) measurements. Furthermore, the CoSe2 CE material exhibits excellent electrochemical stability for catalyzing the reduction of I3−. Our work inspires the development of high efficiency selenides electrode materials for use in the BQDSSCs field.

A highly efficient bilayer graphene/ZnO/silicon nanowire based heterojunction photodetector with broadband spectral response

This paper presents three self-powered photodetectors namely, p+-bilayer graphene (BLG)/n+-ZnO nanowires (NWs), p+-BLG/n+-Si NWs/p–-Si and p+-BLG/n+-ZnO NWs/p–-Si. The Silvaco Atlas TCAD software is utilized to characterize the optoelectronic properties of all the devices and is validated by analytical modeling. The proposed dual-junction photodetectors cover broadband spectral response varying from ultraviolet to near-infrared wavelengths. The dual-heterojunction broadband photodetector exhibits photocurrent switching with the rise and fall time of 1.48 and 1.27 ns, respectively. At −0.5 V bias, the highest external quantum efficiency, photocurrent responsivity, specific detectivity, and the lowest noise equivalent power of 71%, 0.28 A W−1, 4.2 × 1012 cmHz1/2 W−1, and 2.59 × 10–17 W, respectively, are found for the dual-heterojunction device with a wavelength of 480 nm at 300 K. The proposed nanowires based photodetectors offer great potential to be utilized as next-generation optoelectronic devices.

Sensitive and selective photoelectrochemical immunosensing platform based on potential-induced photocurrent-direction switching strategy and a direct Z-scheme CdS//hemin photocurrent-direction switching system

Herein, we develop a novel ultrasensitive and selective photoelectrochemical (PEC) immunosensor based on a potential-induced photocurrent-direction switching of the CdS-chitosan nanoparticles (CdS-CS NPs) and a direct Z-scheme CdS/hemin photocurrent-direction switching system. Taking the detection of Prion (PrPC) as example, the CdS-CS NPs served as photoactive materials showed a cathodic photocurrent by the potential-stimulated switching of the photocurrent direction strategy, after immobilization of the captured antibody of PrPC (Ab1) onto the surface of CdS-CS NPs, nitrogen-doped porous carbon (NPC)-hemin polyhedra labelled with secondary antibody of PrPC (Ab2) were subsequently introduced onto the immunosensing interface due to the antigen−antibody specific recognition, and could act as a photocurrent-direction converter of CdS-CS NPs to produce a big anodic photocurrent which was opposite to that of CdS-CS NPs, owe to the well-matched energy levels between CdS and hemin to form a direct Z-scheme CdS/hemin system. By coupling the potential-stimulated switching of the photocurrent direction strategy and direct Z-scheme photocurrent-direction switching system, PrPC was detected sensitively with a wide linear response range from 4 to 1000 aM and a low detection limit of 0.53 aM. Also, the developed PEC immunosensing platform showed excellent selectivity. Going beyond the conventional “signal-off” or “signal-on” driven immunosensor, this strategy may has promising applications in bioanalysis, disease diagnostics, and clinical biomedicine.

Photocurrent switching on electrophoretic CdSe QD electrodes with different ligands

Photocurrent switching on electrophoretic CdSe QD electrodes with different ligands

Эффект переключения фототока в наноструктурированном анодированном диоксиде титана и изменение его фотоактивности мультислойными полиионными сборками

Эффект переключения фототока в наноструктурированном анодированном диоксиде титана и изменение его фотоактивности мультислойными полиионными сборками

Light intensity-induced photocurrent switching effect

A better control over processes responsible for the photocurrent generation in semiconductors and nanocomposites is essential in the fabrication of photovoltaic devices, efficient photocatalysts and optoelectronic elements. Therefore, new approaches towards photochemical properties tuning are intensively searched for. Among numerous parameters, the photocurrent polarity is of great importance to the overall performance of a device. Usually, the polarity is controlled through an alignment of electronic states/bands, tailoring of applied potential or suitable selection of incident light wavelengths. In most scenarios though, the influence of light intensity is somehow neglected and either some arbitrarily chosen, natural conditions are mimicked or this parameter is varied only in a narrow range. Here we present a ternary nanocomposite in which the persistent photocurrent polarity switching is achieved through changes in the light intensity. We also present arguments suggesting this behaviour is of a general character and should be considered also in other photochemical systems.

Two pyrene-based metal−organic frameworks constructed from 1,3,6,8-tetrakis(p-benzoic acid)pyrene: Syntheses, structures and photoelectron performances

Two pyrene-based metal−organic frameworks directed by ionic liquids, [M2(TBAPy)(H2O)2]·(Guests)x (M ​= ​Co 1, Zn 2) based on a tetratopic linker with a π-conjugated pyrene core, i.e. 1,3,6,8-tetrakis(p-benzoic acid)pyrene (H4TBAPy), have been synthesized under the combination of hydro/solvothermal and ionothermal condition. 1 and 2 are isostructural and feature 2D layered porous network based on M2(O2C)4 paddlewheel units with axially coordinated water molecules. The temperature-dependent fluorescence emission clearly demonstrates the varying degree of interchromophoric interaction as a function of temperature within ​1 ​and ​2. Photoelectron measurements reveal that 1 and 2 both display quick response to visible light irradiation, and are capable of repetitive on-off photocurrent switching with a large on-off ratios. The closely spaced TBAPy chromophores and their higher local concentration along with their twisty molecular conformation would facilitate the formation of excimers, photon capture, electron−hole separation, long-range energy transport and delivery.

An intensity-modulated photocurrent spectroscopy study of the charge carrier dynamics of WO3/BiVO4 heterojunction systems

Synergistic effects as a result of combining different photoactive materials provide a promising pathway to improve the photoelectrochemical performance in heterojunction devices for solar water splitting. The photoelectrochemical characteristics of tungsten trioxide (WO3) and bismuth vanadate (BiVO4) have been studied, comparing the single-phase materials with two heterojunction systems based on a WO3 underlayer and a thin, spin-coated BiVO4 top layer, using two types of underlayer: (i) a nanorod-based WO3 substrate prepared by hydrothermal methods (nr-WO3/BiVO4); and (ii) a spin-coated thin, compact WO3 substrate (pl-WO3/BiVO4). Intensity-modulated photocurrent spectroscopy (IMPS) was used to determine the charge separation efficiency, internal and external quantum efficiencies, and process time constants for the four systems in a phosphate buffer at pH 7, both without and with an added hole scavenger, Na2SO3. The heterojunction systems show excellent performance, which is ascribed to the superior capability of WO3 to extract photogenerated electrons from the BiVO4 film that acts as the main absorber. IMPS convincingly shows that the heterojunction configuration prevents surface recombination at the BiVO4 /electrolyte interface, as well as the detrimental surface modification generally observed for WO3 photoelectrodes. The improved electron transport properties of the nr-WO3 substrate and the large area of the heterojunction interface result in better performance for nr-WO3/BiVO4, where at 455 nm water photo-oxidation is quantitative. For the single-phase BiVO4 photoelectrodes, an interesting photocurrent switching phenomenon is observed in the presence of the hole scavenger, indicating the intricate interplay between electron trapping and hole charge transfer; this phenomenon is prevented by the heterojunction structure because of the rapid electron extraction by WO3. These results show that IMPS gives detailed information on the reasons for the excellent performance of heterojunction systems, providing opportunities to design new, more efficient solar water splitting systems.

Electrical characteristics analysis of PIN detector with different doping concentration levels of N and P-type materials

Present work involves the analysis of electrical characteristics of PIN photodetector with different doping concentration of P and N-type regions which serve as good ohmic contacts. It is possible to improve the basic electronic properties of a PIN photodetector with slight changes in doping levels. So, critical investigation of limit of heavy doping levels of N and P-type materials is very important. Hence this paper illustrates the importance of selecting the optimum value of doping levels when the doping level of intrinsic region remains fixed. Moreover, it provides the analysis of cathode current, recombination rate; electric field; spectral and transient responses of PIN detector to highlight the effect of doping concentration below or beyond the optimum value (1018) for the selected detector. For large photocurrent and fast switching operation there is a need to define the optimum level of the doping concentration of P and N-type layers in PIN detector. In this paper, the performance of Silicon based PIN photodiode’s intensity response within 100–1000 nm wavelength range is demonstrated. The present work will be beneficial in different applications such as detection of light in Ultraviolet range and for high-speed switching circuits.

Photoelectrochemical photocurrent switching effect on a pristine anodized Ti/TiO2 system as a platform for chemical logic devices.

We report here the effect of the photoelectrochemical photocurrent switching (PEPS) observed on highly-ordered pristine anodized Ti/TiO2 for the first time. At negative potential bias, blue irradiation gives cathodic photocurrent, whereas anodic photocurrent was observed for ultraviolet irradiation. We believe this phenomenon is due to the electron pathway provided by Ti3+ defect states.

Photocurrent switching effect on BiVO4 electrodes and its application in development of photoelectrochemical glucose sensor

In this work, we reported the photocurrent switching effect on BiVO4 semiconductor as well as its application for construction of a new cathodic photoelectrochemical (PEC) biosensor. Specifically, the photocurrent switching effect of BiVO4 upon fluorine doped tin oxide (FTO) glass substrate was greatly dependent on its treatment temperature and composition of solution in the cell. The photocurrent transition potential from anode to cathode is ~ 0.38 V (vs SCE) in the presence of O2. H2O2 can act as electron acceptor to improve cathodic PEC current at electrode treated under 500 °C. A cathodic PEC biosensor of glucose was designed based on glucose oxidase (GOD). The GOD/BiVO4/FTO photoelectrode exhibited high sensitivity towards the enzyme reaction production of H2O2. This PEC biosensor shows a good response on the concentration of glucose and exhibits a dynamic range of 1~400 μM with a detection limit of 0.73 μM. Interference from oxygen fluctuation was negligible. The present work provides a promising approach to develop other oxidase-based PEC biosensors.

Highly Dense Packing of Chromophoric Linkers Achievable in a Pyrene-Based Metal-Organic Framework for Photoelectric Response.

Highly dense packing of chromophoric linkers is achieved in a novel pyrene-based metal-organic framework (MOF), [Zn(TBAPy)1/2(H2O)2], induced by an ionic liquid. This MOF displays a quick response to visible-light irradiation (photocurrent density of up to 4.492 μA cm-2) and is capable of repetitive on-off photocurrent switching with a large on-off ratio (37.55).

Ferroicity-driven nonlinear photocurrent switching in time-reversal invariant ferroic materials.

Nonlinear optical responses to external electromagnetic field, characterized by second- and higher-order susceptibilities, play crucial roles in nonlinear optics and optoelectronics. Here, we demonstrate the possibility to achieve ferroicity-driven nonlinear photocurrent switching in time-reversal invariant multiferroics. It is enabled by the second-order current response to electromagnetic field whose direction can be controlled by both internal ferroic orders and external light polarization. Second-order direct photocurrent consists of shift current and circular photocurrent under linearly and circularly polarized light irradiation, respectively. We elucidate the microscopic mechanism in a representative class of two-dimensional multiferroic materials using group theoretical analyses and first-principles theory. The complex interplay of symmetries, shift vector, and Berry curvature governs the fundamental properties and switching behavior of shift current and circular photocurrent. Ferroicity-driven nonlinear photocurrent switching will open avenues for realizing nonlinear optoelectronics, nonlinear multiferroics, etc., using the coupled ferroic orders and nonlinear responses of ferroic materials under external field.

Multimechanism Synergistic Photodetectors with Ultrabroad Spectrum Response from 375 nm to 10 µm.

Broadening the spectral range of photodetectors is an essential topic in photonics. Traditional photodetectors are widely used; however, the realization of ultrabroad spectrum photodetectors remains a challenge. Here, a photodetector constructed by a hybrid quasi‐freestanding structure of organic ferroelectric poly(vinylidene fluoride–trifluoroethylene) (P(VDF‐TrFE)) with molybdenum disulfide (MoS2) is demonstrated. The 2D MoS2 with the ultrathin structure brings a great benefit of heat dissipation for the pyroelectric infrared detector. By coupling the mechanisms of pyroelectrics, photoconductor, and phototransistor effect, an ultrabroad spectrum response ranging from ultraviolet (375 nm) to long‐wavelength infrared (10 µm) is achieved. In the 2.76–10 µm spectral range, the 2D MoS2 is used to read and amplify the photocurrent induced by the pyroelectric effect of P(VDF‐TrFE). The sensitivity of the device in this spectral range is greatly enhanced. A high responsivity of 140 mA W−1, an on/off photocurrent switching ratio up to 103, and a quick response of 5.5 ms are achieved. Moreover, the ferroelectric polarization field dramatically enhances the photoconductive properties of MoS2 and restrains dark current and noise. This approach constitutes a reliable route toward realizing high‐performance photodetectors with a remarkable ultrabroad spectrum response, high responsivity, low power consumption, and room‐temperature operation.

Photocurrent Switching on Electrophoretic CdSe QD Electrodes with Different Ligands

Photoelectrochemical behavior of oleate- and sulfide-capped CdSe QD films fabricated via electrophoretic deposition has been investigated in Na2SO3 aqueous electrolyte. The oleate substitution for sulfide led to considerable increase in photocurrent efficiency. Films of the both types show photocurrent switching under 465-nm light irradiation. The photocurrent direction switching potential strongly depends on the particle size demonstrating negative shift of the potential with size: from 0.0[Formula: see text]V for 2.4[Formula: see text]nm to [Formula: see text][Formula: see text]V for 6.3[Formula: see text]nm.

A self-powered UV photodetector based on polyaniline/titania nanocomposite with long-term stability

Ultraviolet (UV) light photodetectors fabricated from metal oxide semiconductors or conducting polymers due to their inferior electric performances remain insufficient. To overcome this limitation, a conducting polymer/metal oxide semiconductor heterostructure system is one of the significant approaches which can be used. To verify this assumption, polyaniline network (PANI) and p-type polyaniline/n-type titania nanocomposite (PT) were synthesized by chemical oxidative polymerization and used as self-powered UV photodetector (SUP), in the present work. Herein, the SUP devices based on PT (PTD) and PANI (PD) were capable of generating photo-current flow without any need to an external power source. At zero bias, PTD showed superior stable on-off photo-current switching, appropriate responsivity to different UV light power density illumination and appropriate response time, even for months. Our results provide opportunities for developing PTD as a SUP with high-performance and practical use.

Non‐Stoichiometry Induced Switching Behavior of Ferroelectric Photovoltaic Effect in BaTiO3 Ceramics

Ferroelectric photovoltaic (FPV) effect has been studied among a series of non‐stoichiometric BaTiO3 (Ba/Ti = 0.92–1.05) ceramic chips prepared by tape casting method. The FPV performance increases abruptly when the Ba/Ti molar ratio deviates from the stoichiometry within 1%. Meanwhile, a photocurrent direction switching behavior is observed between Ti‐excess and Ba‐excess samples. The TEM analysis shows their significant difference in grain‐boundary (GB), where abnormal GB with a width of 10–15 nm is observed in Ba‐excess sample. The photocurrent switching phenomenon is described to the competition between the asymmetrical Schottky barriers induced PV effect and intrinsic FPV effect. Widen GB in Ba‐excess BaTiO3 ceramics restrains the intrinsic FPV effect and results in the switching behavior. This study offers direct evidence of the vital role of GB in FPV effect and may promote the development of photovoltaic devices.

A new photoelectrochemical immunosensor for ultrasensitive assay of prion protein based on hemin-induced photocurrent direction switching

As a significant biomarker of prion diseases, ultrasensitive assay of infectious isoform of prion (PrPSc) is highly desirable for early diagnostics of prion diseases. Herein, taking normal cellular form of prion (PrPC) as a model owing to a high risk of pathogenicity of PrPSc, a new photoelectrochemical immunosensor has been developed based on hemin-induced switching of photocurrent direction. In the presence of PrPC, nitrogen-doped porous carbon-hemin polyhedra labeled with secondary antibody were introduced onto the CdS-chitosan (CS) nanoparticles-modified indium–tin oxide (ITO) electrode via the antigen–antibody specific recognition. Because of the matched energy level between CdS and hemin, the high-efficiency switch of photocurrent direction of the ITO/CdS-CS photoelectrode from anodic to cathodic photocurrent was observed even at very low concentration (0.4 aM) of PrPC. Through changing the specific antibody, this method can be easily expanded to PrPSc assay. Such low detectable limit is very useful in the early diagnosis and screening of prion diseases. The developed method has also promising applications in bioanalysis, disease diagnostics, and clinical biomedicine.

A sensitive photoelectrochemical assay of miRNA-155 based on a CdSe QDs//NPC-ZnO polyhedra photocurrent-direction switching system and target-triggered strand displacement amplification strategy.

Herein, a new photoelectrochemical (PEC) biosensor based on a photocurrent direction switching system and target-triggered strand displacement amplification strategy was developed for the sensitive detection of microRNA (miRNA)-155, and it showed excellent selectivity and a low detection limit of about 49 aM.

Enhanced Optoelectronic Properties of Bilayer Graphene/HgCdTe-Based Single- and Dual-Junction Photodetectors in Long Infrared Regime

We present novel p + -bilayer graphene (BLG) and mercury cadmium telluride (MCT)-based single- and dual-junction photodetectors, namely, p + -BLG/n - -MCT and p + -BLG/n - -MCT/n + -MCT, operating in long infrared regime. The optoelectronic characterizations utilizing Silvaco Atlas TCAD are validated by analytical modeling. All the devices demonstrate self-powered mode operation and exhibit more than 10 6 times enhancement in photocurrent density. The dual-heterojunction photodetector demonstrates rapid photocurrent switching with the rise and fall time of ~0.05 and ~0.013 ps, respectively, than that of single-heterojunction-based photodetectors. The highest external quantum efficiency (QE ext ), external photocurrent responsivity, and lowest noise equivalent power of 85.8%, 7.33 A/W, and 4.72 × 10 -20 W, respectively, are found for the dual-heterojunction photodetector with a wavelength of 10.6 μm at 77 K. Such optimum photodetection performance is attributed to the presence of a huge amount of electric field (180 kV/cm) at n - -n + heterojunction, which accelerates the photogenerated electrons resulting in effective photocurrent. It is further demonstrated that the temperature-dependent QE ext with values >100% is due to the carrier multiplication effect in BLG.