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 article, the photodeposition (PD) technique was used to incorporate CdS quantum dots (QDs) into mesoporous TiO2 nanocrystalline films.
Abstract: CdS quantum dots (QDs) have been incorporated into mesoporous TiO2 nanocrystalline films by a photodeposition (PD) technique we have recently developed [CdS(PD)/mp-TiO2], and for comparison, the conventional successive ionic layer adsorption and reaction (SILAR) and self-assembled monolayer (SAM) methods have also been used for preparing the coupling system. The most important characterstic of the PD technique is that the efficicent interfacial charge transfer between the semiconductors is guaranteed because the photocatalytic redox property of TiO2 is taken advatage of to form the heteronanojunction. The N2 adsorption−desorption data analysis by the Barret−Joyner−Halenda method and the elemental depth profile by electron probe microanalysis showed that CdS QDs are distributed in the mesopores of the film without pore-blocking in the PD sample and with partial pore-blocking in the SILAR sample, whereas only the upper part of the film is covered with CdS QDs in the SAM sample. The PD technique enables one ...
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TL;DR: The study of optical properties reveals that the band-gap of the CdS nano-particle decreases with increase of sonication time and reach an approximate constant value, and it was observed that nano- particles grew faster at the beginning of sonisation and then reached an almost constant value.
51 citations
TL;DR: CdSe nanoparticles capped with cysteinate, 3-mercaptopropionate, and mercaptosuccinate were adsorbed to TiO(2) from basic aqueous dispersions and exhibit unusual electronic properties and desirable electron-transfer reactivity.
Abstract: CdSe nanoparticles (NPs) capped with cysteinate (Cys), 3-mercaptopropionate (MP), and mercaptosuccinate (MS) were adsorbed to TiO2 from basic aqueous dispersions. Native capping groups served as molecular linkers to TiO2. Thus, the materials-assembly chemistry was simplified and made more reproducible and environmentally benign. The electronic properties of CdSe and the electron-transfer reactivity at CdSe-linker-TiO2 interfaces varied with the structure and functionality of the capping groups. Cys-capped CdSe NPs exhibited a narrow and intense first excitonic absorption band centered at 422 nm, suggesting that they were magic-sized nanocrystals (MSCs) with diameters less than 2 nm. MP- and MS-capped CdSe NPs had broader and lower-energy absorption bands, which are typical of regular quantum dots. Photocurrent action spectra of nanocrystalline TiO2 films functionalized with Cys-CdSe, MP-CdSe, and MS-CdSe overlaid closely with absorption spectra, indicating that excitation of CdSe gave rise to the injectio...
51 citations
TL;DR: In this article, an overview of the orientation behavior of polymer crystals under the influence of one-dimensional and two-dimensional confinement templated by the lamellar and cylindrical microdomains of block copolymers, respectively, is presented.
Abstract: Crystals formed by polymers are typically nanoscale in at least one dimension. The directional control of properties via precise control of the orientations of polymer nanocrystals has strong relevance to technical applications in various areas. Polymer crystals may exhibit preferential orientation when they are formed inside nanoscale domains or pores. Such a confinement-mediated orientation behavior has been a subject of extensive investigation over the past two decades, where a block copolymer in which two or more chemically different sub-chains form a single molecule template system that has received the most attention. In this article, we focus on an overview of the orientation behavior of polymer crystals under the influence of one-dimensional (1-D) and two-dimensional (2-D) confinement templated by the lamellar and cylindrical microdomains of block copolymers, respectively. In the case of lamellae-forming diblock copolymers, both the crystalline–amorphous system (which is composed of one type of nanocrystals) and the more complex double-crystalline diblock (which consists of two types of nanocrystals) are considered. In addition to the templates offered by block copolymers, the preferential orientation of polymer crystals confined in the inorganic anodic aluminium oxide (AAO) nanochannels has also been critically reviewed due to strong relevance to the 2-D confinement effect. Moreover, the significant thermodynamic and kinetic factors governing the crystal orientation behavior have been summarized, which may allow one to understand the strategy for tuning the preferential orientation of polymer nanocrystals under the spatial confinement of different dimensionalities.
51 citations
TL;DR: In this paper, the authors designed and fabricated new catalytic electrodes by combining a PbS nanoparticle catalyst with NiS nanoparticles by a facile chemical bath deposition method and optimized the reaction conditions.
Abstract: The key challenges in boosting the power conversion efficiency (η) of quantum dot-sensitized solar cells (QDSSCs) are efficiently achieving charge separation at the photoanode and enhancing the charge transfer, which is limited by the interface between the polysulfide electrolyte and the counter-electrode (CE). We designed and fabricated new catalytic electrodes by combining a PbS nanoparticle catalyst with NiS nanoparticles by a facile chemical bath deposition method and optimizing the reaction conditions. These were used as CEs for polysulfide redox reactions in CdS/CdSe/ZnS QDSSCs. The PbS nano-morphologies were tuned from nanoparticles to nanospheres by controlling the PbS deposition time on the NiS surface. As the deposition time is increased, the surface morphology, the ratio of Ni:Pb:S, and the thickness of NiS and PbS are affected. The increase in the amount of PbS deposited on the NiS surface could improve the charge transfer at the CE/electrolyte interface. The optimized NiS/PbS composite CE shows a charge transfer resistance (Rct) as low as 10.06 Ω, which is an order of magnitude lower than those of bare NiS (39.65 Ω), PbS (42.12 Ω) and Pt (99.71 Ω) CEs. Therefore, the NiS/PbS composite CEs show much higher catalytic activity for the polysulfide electrolyte than NiS, PbS and Pt CEs. As a result, the QDSSC using this newly synthesized NiS/PbS as a CE achieves a higher power conversion efficiency of 4.52% than the one applying NiS (3.26%) or PbS (3.06%) or Pt (1.29%) CEs. There was no degradation of the efficiency over 10 h under room conditions. This enhancement is mainly attributed to the improved electrocatalytic activity and improved absorption of NiS/PbS, which resulted in the absorption of residual long-wavelength solar irradiation by the PbS CE. This irradiation may have excited the PbS and facilitated the injection of electrons from the conduction band into the polysulfide electrolyte, leading to higher Voc, Jsc, and FF. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Tafel polarization measurements revealed that the composite CEs had better electrocatalytic activity, which improved the rate of polysulfide reduction compared to bare NiS and Pt CEs.
51 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.
9,693 citations
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...
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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