While high photoconductive gain has been recently achieved in graphene-based hybrid phototransistors using semiconductor two-dimensional transition/post-transition metal dichalcogenides or quantum dots sensitizers, obtaining fast photoresponse simutaneously remains a challenge that must be addressed for practical applications. In this paper we report a graphene/GaSe nanosheets hybrid photodetector, in which GaSe nanosheets provide a favorable geometric link to graphene conductive layer through van Der Waals force. After a vacuum annealing process, a high gain in exceeding 107 has been obtained simitaneously with a dynamic response time of around 10 ms for both light on and off. We attribute the high performance to the elimination of possible deep charge traps, most probably at the graphene/GaSe nanosheets interface. This result demonstrates high photoconductive gain and fast photoresponse can be achieved simultaneously and a clean interface is the key to the high performance of these hybrid devices.
Developing electronic doping of colloidal quantum dots is important for basic science and technology. In this article, the doping of colloidal CdSe quantum dots with gallium atoms is reported. Gallium doping of CdSe quantum dots produces important changes in electronic and optical properties of the material. The gallium doping shows a significant impact on the growth kinetics of quantum dots, which reveals important clues about the mechanism of the gallium dopant incorporation into the CdSe. The results show that the gallium doping significantly impacts the conductivity of CdSe thin film made of the quantum dots as well as the photoluminescence and chemical reactivity of the quantum dots, in agreement with the expected ntype character.
The production of nanoparticles on an industrial scale requires an approach other than the widely used hot-injection method. In this work, two heat-up methods are applied to nanoparticle synthesis. The induction heating method produces CdSe quantum dots with ultrasmall properties in seconds. Initial flow-through experiments demonstrate that induction heating continuously produces quantum dots. These results are compared with those from microwave synthesis, which produces quantum dots on a longer timescale but provides fast, continuous heating. Both methods can produce quantum dots within seconds because of rapid heating. In addition, different precursors, single source and separate source, give different results, ultimately providing a handle to control quantum dot properties.
A facile solution-based route is developed for the preparation of distinctive ZnO nanostructures via a dissolution-growth of ZnO nanorods in a saturated ZnS solution at a water-bath temperature of 95 °C. In the dissolution-growth process, a series of novel morphologies including nanotips, tapered and graded nanowires can be conveniently achieved by simply changing the heating time. The pointed ends of the nanotips have a diameter of several nanometers, and the graded nanowires have a gradient change in diameter from a few to tens of nanometers along the longitudinal direction with the size of the thin end matching the Bohr exciton radius of ZnO. Furthermore, the formation mechanism from the ZnO nanorods to the nanotips, to the tapered and graded nanowires is discussed based on shape-evolution observations.
Colloidal CdSe quantum dots show great promise for fabrication of hybrid solar cells with enhanced power conversion efficiency. Here, we demonstrate that gallium-, indium-, tin-doped CdSe quantum dots show significantly improved conductivity and charge carrier density, and also temperature dependent behavior. Furthermore, the doped CdSe hybrid solar cells greatly enhance photocurrent and photovoltage, in which the gallium doped CdSe quantum dots and P3HT bi-layer heterojunction solar cells leads to a maximum power conversion efficiency of 2.0% at elevated temperatures under AM 1.5 solar illumination. All the doped samples exhibit inverted temperature dependent power conversion of the photovoltaic cells, which could be effectively utilized in solar concentrators. The approach presented can be applied to a wide range of doped quantum dots and polymer hybrids and is compatible with solution processing, thereby offering a general tactic for improving the efficiency of quantum dot based solar cells.The so called 3rd generation solar cells have been the interest of the scientific community with a promise of providing cheap and efficient photovoltaic devices. 1-4 One of the 3rd generation solar cell concepts depends on a combination of inorganic and organic photosensitizers. 5-8 The inorganic components can consist of quantum confined semiconductor structures 3, 9 (nanoparticle, nanorod, tetrapods) that are synthesized via colloidal route combined with conductive polymers such as P3HT. 10, 11 Varying the composition, size and shape of the inorganic component these photovoltaic cells allows capturing and utilizing photons from different parts from the solar output. While these solar cells are proven to be functional, it is difficult to manufacture them with high overall power conversion efficiencies; therefore, research needs to focus on concepts that can identify components that are responsible for the lack of improvements.Among the quantum dot (QD) materials, CdSe QDs received significant attention in this quest of producing efficient solar cells. Although CdSe is not a sustainable material, it provides a platform to study many different effects associated with the construction of polymer/inorganic solar cells. 3 In addition, the bandgap of colloidal CdSe QDs (2.6-1.7 eV) overlaps reasonably well with the solar output to capture large portion of the sunlight's energy. There are several reports that show P3HT/CdSe QDs solar cells provide somewhat efficient power conversion efficiencies in the few percent range. 9, 12-25 Recently, Zhou et al. have reached 5.3% record power conversion efficiency in PCPDTBT: CdSe device as a result of removal of trap sites upon the ethanedithiol 10.1149/06615.0001ecst ©The Electrochemical Society ECS Transactions, 66 (15) 1-8 (2015) 1 ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 137.122.8.73 Downloaded on 2015-08-06 to IP
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