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: Cobalt pyrite (cobalt disulfide, CoS2) thin film on glass is reported as a robust, high-performance, low-cost, earth-abundant counter electrode for liquid-junction quantum dot-sensitized solar cells (QDSSCs) that employ the aqueous sulfide/polysulfide redox electrolyte as the hole-transporting medium.
Abstract: We report a cobalt pyrite (cobalt disulfide, CoS2) thin film on glass as a robust, high-performance, low-cost, earth-abundant counter electrode for liquid-junction quantum dot-sensitized solar cells (QDSSCs) that employ the aqueous sulfide/polysulfide (S2–/Sn2–) redox electrolyte as the hole-transporting medium. The metallic CoS2 thin film electrode is prepared via thermal sulfidation of a cobalt film deposited on glass and has been characterized by powder X-ray diffraction and electron microscopy. Using the CoS2 counter electrode, CdS/CdSe-sensitized QDSSCs display improved short-circuit photocurrent density and fill factor, achieving solar light-to-electricity conversion efficiencies as high as 4.16%, with an average efficiency improvement of 54 (±14)% over equivalent devices assembled with a traditional platinum counter electrode. Electrochemical measurements verify that CoS2 shows high electrocatalytic activity toward polysulfide reduction, rationalizing the improved QDSSC performance. CoS2 is also le...
194 citations
TL;DR: An innovative route to harvesting energy by mimicking natural photosynthesis, and is independent of fossil fuels is described.
Abstract: The light reaction in natural photosynthesis is generally recognized as one of the most efficient mechanisms for converting solar energy into other energy sources. We report herein on a novel strategy for generating H2 fuel via an artificial Z-scheme mechanism by mimicking the natural photosynthesis that occurs in green plants. Designing a desirable photocatalyst by mimicking the Z-scheme mechanism leads to a conduction band that is sufficiently high to reduce protons, thus decreasing the probability of charge recombination. We combined two visible light sensitive photocatalysts, CdS and carbon-doped TiO2, with different band structures. The used of this combination, that is, CdS/Au/TiO1.96C0.04, resulted in the successful transfer of photogenerated electrons to a higher energy level in the form of the letter ‘Z’. The system produced about a 4 times higher amount of H2 under irradiation by visible light than CdS/Au/TiO2. The findings reported herein describe an innovative route to harvesting energy by mim...
193 citations
TL;DR: In this article, a dye-sensitized solar cell involves colloidal semiconductor quantum dots that serve as antennas, funneling absorbed light to the charge separating dye molecules via nonradiative energy transfer.
Abstract: A new design of dye-sensitized solar cells involves colloidal semiconductor quantum dots that serve as antennas, funneling absorbed light to the charge separating dye molecules via nonradiative energy transfer. The colloidal quantum dot donors are incorporated into the solid titania electrode resulting in high energy transfer efficiency and significant improvement of the cell stability. This design practically separates the processes of light absorption and charge carrier injection, enabling us to optimize each of these separately. Incident photon-to-current efficiency measurements show a full coverage of the visible spectrum despite the use ofaredabsorbingdye,limitedonlybytheefficiencyofchargeinjectionfromthedyetothetitaniaelectrode.Time resolved luminescence measurements clearly relate this to Forster resonance energy transfer from the quantum dots to the dye. The presented design introduces new degrees of freedom in the utilization of quantum dot sensitizers for photovoltaic cells. In particular, it opens the way toward the utilization of new materials whose band offsets do not allow direct charge injection.
193 citations
TL;DR: The focus is on the recent developments of supramolecular systems for light energy conversion, which are mainly composed of porphyrin dyes and nanocarbon materials, such as fullerenes and carbon nanotubes.
Abstract: Recent developments in synthetic and supramolecular techniques have made it possible to control precisely, organize and arrange molecules at the nanometre level. Such synthetic and supramolecular strategies enable us to construct photofunctional molecular architectures for light energy conversion, such as photovoltaics. In photovoltaic cells, processes such as light-harvesting, charge separation for carrier generation, and carrier transport are generally required. Therefore, the construction of supramolecular assemblies based on these three processes is interesting and promising for the future development of photovoltaics. In this perspective, the focus is on the recent developments of supramolecular systems for light energy conversion, which are mainly composed of porphyrin dyes and nanocarbon materials, such as fullerenes and carbon nanotubes. The specific topics are as follows: (i) preparation, photodynamics, and photoelectrochemistry of self-assembled porphyrin nanoparticles prepared by simple blend, (ii) highly organized supramolecular nanoassemblies of porphyrins and fullerenes using gold nanoparticles, dendritic and polypeptide structures, (iii) the supramolecular formation and photoelectrochemical property of carbon nanotubes, and (iv) supramolecular photofunctional nanorods of porphyrins.
192 citations
TL;DR: In this paper, a composite photocatalysts composed of reduced graphene oxide (RGO) sheets, CdS nanoparticles (CNPs), and ZnO nanorods were developed using a simple low-temperature chemical approach.
Abstract: a b s t r a c t Novel composite photocatalysts composed of reduced graphene oxide (RGO) sheets, CdS nanoparticles (CNPs), and ZnO nanorods were developed using a simple low-temperature chemical approach. The RGO sheets and CNPs were sensitized via single-step chemical bath deposition at 70 ◦ C. Because of the incorporation of RGO into the CdS and ZnO structures, the photodegradation performance toward methylene blue (MB) degradation under visible light illumination was significantly improved compared with that of just CdS and ZnO. The highest kinetic rate constant (k = 0.028 min −1 ) using 0.20 wt% of added RGO was four times higher than that without graphene. This composite degraded MB within 40 min. Such improved performance resulted from effective separation of electron-hole pairs by the RGO sheets. Photoluminescence quenching, increased optical absorbance, and high specific surface area (23.08 m2 g−1) also contributed to the high degradation efficiency. An energy level diagram was constructed to explain how the RGO sheets minimized the recombination rate. The developed RGO–CdS–ZnO composites have a potential application in water purification devices.
191 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.
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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...
9,086 citations
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