Jinzhong Xiang

Chlorine doped graphene quantum dots: Preparation, properties, and photovoltaic detectors

Graphene quantum dots (GQDs) are becoming one of the hottest advanced functional materials because of the opening of the bandgap due to quantum confinement effect, which shows unique optical and electrical properties. The chlorine doped GQDs (Cl-GQDs) have been fabricated by chemical exfoliation of HCl treated carbon fibers (CFs), which were prepared from degreasing cotton through an annealing process at 1000 °C for 30 min. Raman study shows that both G and 2D peaks of GQDs may be redshifted (softened) by chlorine doping, leading to an n-type doping. The first vertical (Cl)-GQDs based photovoltaic detectors have been demonstrated, both the light absorbing and electron-accepting roles for (Cl)-GQDs in photodetection have been found, resulting in an exceptionally big ratio of photocurrent to dark current as high as ∼105 at room temperature using a 405 nm laser irradiation under the reverse bias voltage. The study expands the application of (Cl)-GQDs to the important optoelectronic detection devices.

Fabrication and properties of a high-performance chlorine doped graphene quantum dot based photovoltaic detector

Functionalized graphene quantum dot (GQD) based materials play an important role in the development of high-performance, low-cost, large-area optoelectronic devices. The progress, however, is impeded by the poor understanding of the physical mechanism for GQDs in these devices. In this paper, chlorine doped GQD (Cl-GQD) based photovoltaic photodetectors have been fabricated using a solution process, and it was found that the presence of Cl-GQDs can significantly enhance the performance of the device. The improved performance of Cl-GQD based devices has been investigated by systematically studying the structural, morphological, optical, electrical, electrochemical and photoelectrical properties. The important photovoltaic detectors parameters such as the saturation current densities (J0), barrier heights (Φb), built-in potentials (Vbi), carrier concentrations (N) and depletion layer widths (Wd) have been calculated and discussed by studying the I–V and C–V characteristics under different illuminations. The frequency dependent capacitance and conductance have also been discussed. The results provide guidance for developing high-performance graphene based optoelectronic devices.

An extreme high-performance ultraviolet photovoltaic detector based on a ZnO nanorods/phenanthrene heterojunction

Ultraviolet (UV) photodetectors are important optoelectronic devices. The development of a high-performance UV detector, however, has been impeded by lack of stable p-type wide gap semiconductors. Herein, an extremely high UV response for a ZnO nanorods/phenanthrene (Phen) photovoltaic detector has been realized, utilizing phenanthrene as a p-type wide gap organic semiconductor; a detectivity (D*) as high as ∼9.0 × 1013 cm Hz1/2 W−1 has been reached, showing significant potential for optoelectronic applications.

Facile preparation of sulphur-doped graphene quantum dots for ultra-high performance ultraviolet photodetectors

Sulphur-doped graphene quantum dots (S-GQDs) were prepared in this work by a novel and facile method using the co-combustion (T-X-J method) of a liquid mixture of paraffin oil and carbon disulphide (CS2). Ultra-high performance (R: 307 A W−1; D*: 1.5 × 1014 Jones) ultraviolet photodetectors based on S-GQDs were fabricated under ambient conditions, shedding light on the fabrication of graphene based high-performance optoelectronic devices.

Solution processable high-performance infrared organic photodetector by iodine doping

Solution processable high-performance, large-area, low-cost infrared organic photodetectors (OPDs) have been receiving more and more attention for their important applications both in scientific and technological fields. The search for a simple method to upgrade device performance for OPDs becomes increasingly important. Here, the performance of an OPD in the near-infrared (NIR) region is tremendously improved by doping iodine into the devices active layer (P3HT:PCBM:I2), 2.7 wt% iodine doping may increase the absorption by 31.3% for the active film and result in a ∼11 000-fold increase in responsivity for the detector. A high detectivity (D*) of ∼1.6 × 1012 cm Hz1/2 W−1, a good specific responsivity (R) of ∼80 A W−1 and a large EQE (external quantum efficiency) of 120% are achieved under illumination (λ = 850 nm) at room temperature. Systematic characterizations reveal that iodine-doping can introduce acceptor states in the energy band gap for the polymer layer, and thus increase the harvesting to long wavelength photons. A small dose of iodine doping can significantly induce improvement in device performance. This work demonstrates a simple but feasible method to enhance an NIR optoelectronics device.

High performance ultraviolet photodetectors based on ZnO nanoflakes/PVK heterojunction

A high performance ultraviolet (UV) photodetector is receiving increasing attention due to its significant applications in fire warning, environmental monitoring, scientific research, astronomical observation, etc. The enhancement in performance of the UV photodetector has been impeded by lacking of a high-efficiency heterojunction in which UV photons can efficiently convert into charges. In this work, the high performance UV photodetectors have been realized by utilizing organic/inorganic heterojunctions based on a ZnO nanoflakes/poly (N-vinylcarbazole) hybrid. A transparent conducting polymer poly(3,4-ethylene-dioxythiophene):poly(styrenesulfonate)-coated quartz substrate is employed as the anode in replacement of the commonly ITO-coated glass in order to harvest shorter UV light. The devices show a lower dark current density, with a high responsivity (R) of 7.27 × 103 A/W and a specific detectivity (D*) of 6.20 × 1013 cm Hz1/2/W−1 at 2 V bias voltage in ambient environment (1.30 mW/cm2 at λ = 365 nm), ...

Functionalization of graphene quantum dots by fluorine: Preparation, properties, application, and their mechanisms

Graphene quantum dots (GQDs) possess unique photoelectronic properties ascribed to quantum confinement and edge effects, which have evoked important development and wide application in the optoelectronic field. Doping GQDs with heteroatoms can further modulate the energy band structure and thus produce unexpected properties. Herein, we obtained fluorine-doped GQDs (F-GQDs) by adopting an effective preparation technique, which includes the treatment of the as-prepared reaction precursor, fluorinated carbon fibers, with ultrasonic liquid phase exfoliation. The proposed method is simple, handy, and low-cost, opening up an alternate approach to prepare F-GQDs. Through multiple characterization techniques, the effective incorporation of fluorine in GQDs was confirmed, and the as-prepared F-GQDs exhibit excellent photoelectrical properties and good ultraviolet absorption performances. Accordingly, we have fabricated a vertical photovoltaic UV detector based on F-GQDs. The unoptimized device has an exceptionally...

Solution processable organic/inorganic hybrid ultraviolet photovoltaic detector

Ultraviolet (UV) photodetector is a kind of important optoelectronic device which can be widely used in scientific and engineering fields including astronomical research, environmental monitoring, forest-fire prevention, medical analysis, and missile approach warning etc. The development of UV detector is hindered by the acquirement of stable p-type materials, which makes it difficult to realize large array, low-power consumption UV focal plane array (FPA) detector. Here, we provide a novel structure (Al/Poly(9,9-di-n-octylfuorenyl-2,7-diyl)(PFO)/ZnO/ITO) to demonstrate the UV photovoltaic (PV) response. A rather smooth surface (RMS roughness: 0.28 nm) may be reached by solution process, which sheds light on the development of large-array, light-weight and low-cost UV FPA detectors.

Large-area uniform electron doping of graphene by Ag nanofilm

Graphene has attracted much attention at various research fields due to its unique optical, electronic and mechanical properties. Up to now, graphene has not been widely used in optoelectronic fields due to the lack of large-area uniform doped graphene (n-doped and p-doped) with smooth surface. Therefore, it is rather desired to develop some effective doping methods to extend graphene to optoelectronics. Here we developed a novel doping method to prepare large-area (> centimeter scale) uniform doped graphene film with a nanoscale roughness(RMS roughness ∼1.4 nm), the method (nano-metal film doping method) is simple but effective. Using this method electron doping (electron-injection) may be easily realized by the simple thermal deposition of Ag nano-film on a transferred CVD graphene. The doping effectiveness has been proved by Raman spectroscopy and spectroscopic ellipsometry. Importantly, our method sheds light on some potential applications of graphene in optoelectronic devices such as photodetectors, ...

Exceptional ultraviolet photovoltaic response of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline based detector

UV photodetector is a kind of important optoelectronic devices that has vital applications in both scientific and engineering fields. The development of UV photodetectors has been impeded because of lacking stable p-type wide-gap semiconductor which is crucial for high-performance, low-cost, large-array UV photovoltaic detector. In this paper, we report a novel UV photovoltaic detector fabricated using 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) as a sole photoactive material. The highest detectivity (D*) reaches 9.02 × 1011 cm Hz1/2 W−1 at −1 V bias voltage at room temperature under 365 nm illumination for the un-optimized BCP based detector (without using pre-amplifier), which is the highest value for the sole UV organic photoactive material based photovoltaic detector. The optical, electrical, and photovoltaic properties, including the UV absorption, photoluminescence (PL) emission, PL excitation, I-V, C-V, and photoresponse, have been systematically investigated to disclose the internal mechan...