Recent Advances in Graphene Homogeneous p–n Junction for Optoelectronics

Graphene has been widely used as electrodes and active layers in optoelectronics due to its diverse excellent performances, such as high mobility, large thermal conductivity, and high specific surface area. Methodology for constructing p–n junction has become an important consideration in improving the performance of optoelectronic devices and broadening of its application in related fields. Currently, graphene‐based p–n junctions have been explored and different structures have also been investigated. Herein, the recent progress on graphene homogeneous p–n junction is summarized, ranging from preparation of front‐end materials (e.g., p‐ and n‐type graphene) to building of planar and vertical p–n junctions. Furthermore, p–n junction via electrical modulation is described. The requirements for building the graphene homogeneous p–n junction, and the advantages and drawbacks of the different structures of the p–n junction are also discussed. Finally, a preferential technique to fabricate high performance p‐ and n‐type graphene and building of the p–n junction is evaluated. This paper therefore provides an important indication on the future direction on the application of graphene in optoelectronics

High-performance self-powered ultraviolet photodetector based on PVK/amorphous-WO3 organic-inorganic heterojunction

Ultraviolet (UV) photodetectors have found wide-ranging applications, ranging from optical communications to chemical detection. High performance UV photodetectors that can be self-powered are highly desirable in many applications as they can minimize energy consumption during operation. Herein, a self-powered UV photodetector, which consisted of poly(9-vinylcarbazole) (PVK)/amorphous-WO3 organic-inorganic heterojunction with PEDOT:PSS as a hole transport layer, was fabricated using a two-step method at low temperature. The effect of WO3, PVK and PEDOT:PSS films on the performances of the photodetector was also investigated. Under optimized parameters, the PEDOT:PSS/PVK/WO3 photodetector exhibited a maximum responsivity of 12.41 AW−1, specific detectivity of 1.80 × 1013 Jones, photo-dark current ratio of 103 at reverse bias and typical rectification characteristic when exposed to 365 nm light irradiation. The photoelectric conversion mechanism of this novel PVK/WO3 heterojunction is discussed using energy band diagrams. This work presents a method to produce a high performance WO3-based heterostructure at low temperature, which has the potential for UV imaging

Infrared photodetector based on GeTe nanofilms with high performance

GeTe is an important narrow band gap semiconductor material, which has found application in the fields of thermoelectricity, phase change storage as well as switch. However, it has not been studied for application in the field of photodetectors. Here, GeTe thin films were grown by magnetron sputtering and their material structure, optical and electrical properties were compared before and after annealing. High-performance photodetectors with detectivity of ∼1013 Jones at 850 nm light were demonstrated. Thus the novel, to the best of our knowledge, application of GeTe in optoelectronic devices is reported in this work

The research progress and application of novel terahertz detectors

Terahertz waves have many unique electrical and optical properties, which have significant applications in both civil and military fields, such as physics, biology, public safety inspection, local area communication, information security, environmental monitoring, non-destructive testing and defense technology etc. Terahertz detector is one of the core components in a terahertz system. Therefore, its application is usually determined by the characteristic and performance of the detector. In recent years, there are some major breakthroughs in the development of terahertz detectors. However, there are still technology challenges that limit the application of such device. For example, room temperature terahertz detectors exhibited a large noise equivalent power and low sensitivity. This is in contrast to cooled terahertz detectors, which demonstrated high response rate and low noise equivalent power, but they cannot be miniaturized and are costly. This paper provides a summary and discussion on the recent development and application of terahertz detectors from the aspect of material preparation and device configuration

Facile synthesis of ZnS quantum dots at room temperature for ultra-violet photodetector applications

Zinc sulfide (ZnS) quantum dots (QDs) were synthesized using a facile, low-cost and environmentally friendly method at room temperature and ambient pressure. The structural, optical and electrical properties of the as-prepared ZnS QDs were investigated. The monodispersed crystalline ZnS QDs with an average size of 3.8 nm has been prepared, an absorption peak at 292 nm in the ultra-violet (UV) range was observed. The maximum responsivity (R) and detectivity (D*) of the ZnS QDs based photodetector under 365 nm UV light illumination were 5.8 A W−1 and 1.97×1013 Jones, respectively, which shows important potential application in UV detection

Preparation and photoelectric properties of SnOx films with tunable optical bandgap

SnOx thin films with tunable optical bandgap were prepared using RF magnetron sputtering. The bandgap was adjustable between 2.16 and 3.96 eV depending on oxygen partial pressure during deposition and heat treatment. The structure and properties of the SnOx films were studied. The optical absorption of the SnOx films covered multiple ultraviolet bands, such as UVA, UVB and UVC. A photodetector based on the annealed SnOx film exhibited a detectivity of 1 × 1011 Jones (under 365 nm UV light) at room temperature, which demonstrates the important potential application of SnOx films for UV detection

Preparation and photoelectric properties of cadmium sulfide quantum dots

Cadmium sulfide quantum dots (CdS QDs) are widely used in solar cells, light emitting diodes, photocatalysis, and biological imaging because of their unique optical and electrical properties. However, there are some drawbacks in existing preparation techniques for CdS QDs, such as protection of inert gas, lengthy reaction time, high reaction temperature, poor crystallinity, and non-uniform particle size distribution. In this study, we prepared CdS QDs by liquid phase synthesis under ambient room temperature and atmospheric pressure using sodium alkyl sulfonate, CdCl2, and Na2S as capping agent, cadmium, and sulfur sources respectively. This technique offers facile preparation, efficient reaction, low-cost, and controllable particle size. The as-prepared CdS QDs exhibited good crystallinity, excellent monodispersity, and uniform particle size. The responsivity of CdS QDs-based photodetector is greater than $0.3\,{\rm{\mu }}{\rm{A}}/{\rm{W}}$, which makes them suitable for use as ultra-violet (UV) detectors

Recent Advances on Electrochemical Sensors for the Detection of Organic Disinfection Byproducts in Water

Irreversible organ damage or even death frequently occurs when humans or animals unknowingly drink contaminated water. Therefore, in many countries drinking water is disinfected to ensure removal of harmful pathogens from drinking water. If upstream water treatment prior to disinfection is not adequate, disinfection byproducts (DBPs) can be formed. DBPs can exist as wide variety of compounds, but up until now, only several typical compounds have drinking water standards attributed to them. However, it is apparent that the range of DBPs present in water can comprise hundreds of compounds, some of which are at high enough concentrations to be toxic or potentially carcinogenic. Hence, it becomes increasingly significant and urgent to develop an accessible, affordable, and durable sensing platform for a broader range and more sensitive detection of DBPs. Compared with well-established laboratory detection techniques, electrochemical sensing has been identified as a promising alternative that will provide rapid, affordable, and sensitive DBP monitoring in remote water sources. Therefore, this Review covers current state-of-the-art development (within the past decade) in electrochemical sensing to detect organic DBPs in water, which covered three major aspects: (1) recognition mechanism, (2) electrodes with signal amplification, and (3) signal read-out techniques. Moreover, comprehensive quality assessments on electrochemical biosensors, including linear detection range, limit of detection (LoD) and recovery, have also been summarized