Quantum Dot Solar Cells. Semiconductor Nanocrystals as Light Harvesters
18 Oct 2008-Journal of Physical Chemistry C (American Chemical Society)-Vol. 112, Iss: 48, pp 18737-18753
TL;DR: In this paper, three major ways to utilize semiconductor dots in solar cell include (i) metal−semiconductor or Schottky junction photovoltaic cell, (ii) polymer−smiconductor hybrid solar cell, and (iii) quantum dot sensitized solar cell.
Abstract: The emergence of semiconductor nanocrystals as the building blocks of nanotechnology has opened up new ways to utilize them in next generation solar cells. This paper focuses on the recent developments in the utilization of semiconductor quantum dots for light energy conversion. Three major ways to utilize semiconductor dots in solar cell include (i) metal−semiconductor or Schottky junction photovoltaic cell (ii) polymer−semiconductor hybrid solar cell, and (iii) quantum dot sensitized solar cell. Modulation of band energies through size control offers new ways to control photoresponse and photoconversion efficiency of the solar cell. Various strategies to maximize photoinduced charge separation and electron transfer processes for improving the overall efficiency of light energy conversion are discussed. Capture and transport of charge carriers within the semiconductor nanocrystal network to achieve efficient charge separation at the electrode surface remains a major challenge. Directing the future resear...
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TL;DR: In this paper, a universal framework is provided to describe the recent progress in this advanced field and it includes discussions of novel materials, new device configurations and the wide variety of device applications.
Abstract: As Moore's law predicted, field-effect transistors (FETs) have been decreasing in size for several decades. In the process, these devices have suffered considerably from short-channel effects and surface instabilities. Low-dimensional materials, such as 0D quantum dots, 1D nanowires and nanotubes, and 2D nanosheets, would be helpful in the device downscaling process while also enhancing device performance, and have therefore been widely applied in many recently designed FETs. Since the 1990s, more than five million studies related to low-dimensional materials-based FETs have been published. In this article, a universal framework is provided to describe the recent progress in this advanced field and it includes discussions of novel materials, new device configurations and the wide variety of device applications.
30 citations
TL;DR: The latest research by both this group and other groups on the key scenarios under which nanocrystals can engage in energy transfer with other nanoparticles, organic fluorophores, and plasmonic nanostructures are discussed, highlighting potential technological benefits to be gained from such processes.
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TL;DR: In this paper, a highly crystalline Nb3O7F nanostructured film composed of a bottom single crystal nanosheet layer with ca. 1.5 μm thickness and a top microsphere layer with 18.5 µm thickness has been successfully fabricated on a FTO conducting substrate through a facile and one-pot hydrothermal method.
Abstract: A highly crystalline Nb3O7F nanostructured film composed of a bottom single crystal nanosheet layer with ca. 1.5 μm thickness and a top microsphere layer with ca. 18.5 μm thickness has been successfully fabricated on a FTO conducting substrate through a facile and one-pot hydrothermal method. The top Nb3O7F microspheres with 2–5 μm diameter consist of transparent single crystal nanosheets with 10–40 nm thickness. Without the need for further calcination, the as-synthesised Nb3O7F nanostructured films possess excellent crystallinity and high mechanical stability, which can be directly used as photoanodes for CdS quantum dot-sensitised solar cells (QDSSCs) and dye-sensitised solar cells (DSSCs). The transparent single crystal nanosheets constituting top Nb3O7F microspheres possess exposed (100) and (010) surfaces, which can play an important role in sensitiser loading. The photoelectrochemical measurements indicate that the CdS quantum dot-sensitised Nb3O7F nanostructured photoanode with seven chemical bath deposition (CBD) cycles (NbCdS-7) shows the best performance under visible light irradiation (λ > 400 nm) due to higher carrier concentration and longer electron lifetime in NbCdS-7. QDSSCs made of NbCdS-7 photoanodes show an overall light conversion efficiency of 1.68%, which is almost 1.4 and 1.9 times of the NbCdS-5 and NbCdS-10 photoanodes, respectively. DSSC measurement indicates that an overall light conversion efficiency of 2.78% can be achieved for the Nb3O7F nanostructured photoanode. This work demonstrates the possibility of direct growth of a highly crystalline metal oxide-based nanostructured film on a FTO conducting substrate as a photoanode material without the need for further calcination for solar energy conversion applications.
30 citations
TL;DR: In this article, germanium electrodeposits are galvanostatically electroplated anodically onto p-doped Si100 wafers for three different current densities under ambient conditions.
Abstract: In this work, we report studies of germanium electrodeposits galvanostatically electroplated anodically onto p-doped Si100 wafers for three different current densities under ambient conditions. The electrodeposition is carried out in ethylenediamine solutions of K4Ge9, which contain deltahedral Ge9 n� n = 2, 3, 4 Zintl anions. The observed current efficiencies of the deposition are at least 2 orders of magnitude higher than those of cathodic electroplating reported. The samples were characterized by scanning electron microscopy SEM, energy-dispersive X-ray analysis, X-ray photoemission spectroscopy, and mass spectrometry. Their morphology is sheetlike with overlayers of aggregated particles with a median particle size of 225 nm. The overlayer spread increases progressively with increasing current densities. Cross-sectional SEM measurements indicate film thicknesses in the range of 60–320 nm. Electrolytic electrodeposition carried out at 100 V for the same concentration reveals a very similar morphology with significant enhancement in thickness of up to 6 m and median particle size of 625 nm. X-ray diffraction shows that the as-deposited samples are amorphous; however, high temperature annealing results in the crystallization of elemental germanium in the thicker samples 320 nm and 6 m.
30 citations
National Physical Laboratory1, National Institute of Metrology Standardization and Industrial Quality2, University of Washington3, Bundesanstalt für Materialforschung und -prüfung4, Pacific Northwest National Laboratory5, Imperial College London6, Korea Research Institute of Standards and Science7, Instituto Politécnico Nacional8, Lehigh University9, Thermo Fisher Scientific10, University of Nottingham11, MESA+ Institute for Nanotechnology12, University of Manchester13, Xi'an Jiaotong-Liverpool University14
TL;DR: The study identified a need for more consistency in instrumental transmission functions and relative sensitivity factors, since this contributed a variability of 33 % to the VAMAS results.
Abstract: We report the results of a Versailles Project on Advanced Materials and Standards (VAMAS) interlaboratory study on the measurement of the shell thickness and chemistry of nanoparticle coatings. Peptide-coated gold particles were supplied to laboratories in two forms: a colloidal suspension in pure water and particles dried onto a silicon wafer. Participants prepared and analyzed these samples using either X-ray photoelectron spectroscopy (XPS) or low energy ion scattering (LEIS). Careful data analysis revealed some significant sources of discrepancy, particularly for XPS. Degradation during transportation, storage, or sample preparation resulted in a variability in thickness of 53%. The calculation method chosen by XPS participants contributed a variability of 67%. However, variability of 12% was achieved for the samples deposited using a single method and by choosing photoelectron peaks that were not adversely affected by instrumental transmission effects. The study identified a need for more consistency in instrumental transmission functions and relative sensitivity factors since this contributed a variability of 33%. The results from the LEIS participants were more consistent, with variability of less than 10% in thickness, and this is mostly due to a common method of data analysis. The calculation was performed using a model developed for uniform, flat films, and some participants employed a correction factor to account for the sample geometry, which appears warranted based upon a simulation of LEIS data from one of the participants and comparison to the XPS results.
30 citations
References
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TL;DR: In this article, an upper theoretical limit for the efficiency of p−n junction solar energy converters, called the detailed balance limit of efficiency, has been calculated for an ideal case in which the only recombination mechanism of holeelectron pairs is radiative as required by the principle of detailed balance.
Abstract: In order to find an upper theoretical limit for the efficiency of p‐n junction solar energy converters, a limiting efficiency, called the detailed balance limit of efficiency, has been calculated for an ideal case in which the only recombination mechanism of hole‐electron pairs is radiative as required by the principle of detailed balance. The efficiency is also calculated for the case in which radiative recombination is only a fixed fraction fc of the total recombination, the rest being nonradiative. Efficiencies at the matched loads have been calculated with band gap and fc as parameters, the sun and cell being assumed to be blackbodies with temperatures of 6000°K and 300°K, respectively. The maximum efficiency is found to be 30% for an energy gap of 1.1 ev and fc = 1. Actual junctions do not obey the predicted current‐voltage relationship, and reasons for the difference and its relevance to efficiency are discussed.
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TL;DR: Many potential applications have been proposed for carbon nanotubes, including conductive and high-strength composites; energy storage and energy conversion devices; sensors; field emission displays and radiation sources; hydrogen storage media; and nanometer-sized semiconductor devices, probes, and interconnects.
Abstract: Many potential applications have been proposed for carbon nanotubes, including conductive and high-strength composites; energy storage and energy conversion devices; sensors; field emission displays and radiation sources; hydrogen storage media; and nanometer-sized semiconductor devices, probes, and interconnects. Some of these applications are now realized in products. Others are demonstrated in early to advanced devices, and one, hydrogen storage, is clouded by controversy. Nanotube cost, polydispersity in nanotube type, and limitations in processing and assembly methods are important barriers for some applications of single-walled nanotubes.
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TL;DR: In this paper, the carrier collection efficiency and energy conversion efficiency of polymer photovoltaic cells were improved by blending of the semiconducting polymer with C60 or its functionalized derivatives.
Abstract: The carrier collection efficiency (ηc) and energy conversion efficiency (ηe) of polymer photovoltaic cells were improved by blending of the semiconducting polymer with C60 or its functionalized derivatives. Composite films of poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) and fullerenes exhibit ηc of about 29 percent of electrons per photon and ηe of about 2.9 percent, efficiencies that are better by more than two orders of magnitude than those that have been achieved with devices made with pure MEH-PPV. The efficient charge separation results from photoinduced electron transfer from the MEH-PPV (as donor) to C60 (as acceptor); the high collection efficiency results from a bicontinuous network of internal donor-acceptor heterojunctions.
9,611 citations
TL;DR: In this paper, the authors describe recent progress in the theory of nanoparticle optical properties, particularly methods for solving Maxwell's equations for light scattering from particles of arbitrary shape in a complex environment.
Abstract: The optical properties of metal nanoparticles have long been of interest in physical chemistry, starting with Faraday's investigations of colloidal gold in the middle 1800s. More recently, new lithographic techniques as well as improvements to classical wet chemistry methods have made it possible to synthesize noble metal nanoparticles with a wide range of sizes, shapes, and dielectric environments. In this feature article, we describe recent progress in the theory of nanoparticle optical properties, particularly methods for solving Maxwell's equations for light scattering from particles of arbitrary shape in a complex environment. Included is a description of the qualitative features of dipole and quadrupole plasmon resonances for spherical particles; a discussion of analytical and numerical methods for calculating extinction and scattering cross-sections, local fields, and other optical properties for nonspherical particles; and a survey of applications to problems of recent interest involving triangula...
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TL;DR: Semiconductor nanocrystals prepared for use as fluorescent probes in biological staining and diagnostics have a narrow, tunable, symmetric emission spectrum and are photochemically stable.
Abstract: Semiconductor nanocrystals were prepared for use as fluorescent probes in biological staining and diagnostics. Compared with conventional fluorophores, the nanocrystals have a narrow, tunable, symmetric emission spectrum and are photochemically stable. The advantages of the broad, continuous excitation spectrum were demonstrated in a dual-emission, single-excitation labeling experiment on mouse fibroblasts. These nanocrystal probes are thus complementary and in some cases may be superior to existing fluorophores.
8,542 citations