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, two photophysical mechanisms, hot carrier equilibration and carrier multiplication, are proposed for solar cells with power conversion efficiency theoretically exceeding the Shockley-Queisser limit.
Abstract: We summarize our recent explorations of photophysical mechanisms that may be utilized in solar cells with power conversion efficiency theoretically exceeding the Shockley–Queisser limit. The dominant losses responsible for the Shockley–Queisser limit are below band-gap and thermalization (hot carrier) losses; together, they account for >55% of the total absorbed solar energy. This perspective focuses on two photophysical mechanisms, hot carrier equilibration and carrier multiplication, which may be used to reduce these losses through their utilization in novel solar cell designs. For the implementation of a hot carrier solar cell, we discuss the necessity of hot carrier scattering as well as the photon flux challenge. Although recent experiments have demonstrated the feasibility of hot-electron extraction from photo-excited semiconductor nano-crystals, the photon flux challenge cannot be met in these materials. We propose graphene and related materials as potentially ideal chromophores for hot carrier solar cells. For the multi-exciton solar cell, we focus on the molecular analog called singlet fission. Recent experiments in our lab revealed a quantum coherent mechanism in which photo-excitation of the organic semiconductor pentacene or tetracene creates a quantum superposition of singlet exciton and multi-exciton states. This quantum superposition and the corresponding decoherence time (i.e., singlet fission time) are critical to the competing dynamics of charge or energy harvesting. We discuss design principles for solar cells based on singlet fission materials.
104 citations
TL;DR: In 2S3 ALD with indium acetylacetonate (In(acac)3) and H2S was studied with quartz crystal microbalance (QCM), X-ray reflectivity (XRR), and Fourier transform infrared (FTIR) spectroscopy techniques as discussed by the authors.
Abstract: In2S3 atomic layer deposition (ALD) with indium acetylacetonate (In(acac)3) and H2S was studied with quartz crystal microbalance (QCM), X-ray reflectivity (XRR), and Fourier transform infrared (FTIR) spectroscopy techniques. Subsequent In2S3 ALD on TiO2 nanotube arrays defined a model semiconductor sensitized solar cell. For In2S3 ALD on initial Al2O3 ALD surfaces, the In2S3 ALD displayed a nucleation period of ∼60−70 cycles followed by a linear growth region. These results were obtained under ALD conditions that were not completely self-limiting for the In(acac)3 exposure because of the low In(acac)3 vapor pressure. The growth per cycle decreased at higher temperature over the temperature range from 130 to 170 °C at these same reactant conditions. The growth per cycle was 0.30−0.35 A per cycle at 150 °C as determined by QCM and XRR measurements at higher In(acac)3 exposures where the surface reactions were self-limiting chemistry versus In(acac)3 and H2S exposures. The FTIR examinations revealed that the...
104 citations
TL;DR: In this paper, a comprehensive description of different synthetic strategies is presented, with a special emphasis on the formation mechanism, in particular, the pathway followed by nanocrystallites to self-assemble into a spherical structure.
104 citations
TL;DR: The observed relationship between driving force and rate for interfacial hole transfer from quantum dots (QDs) can be used to design QD-molecular systems that maximize interfacial charge transfer rates while minimizing energetic losses associated with the driving force.
Abstract: We have investigated the relationship between driving force and rate for interfacial hole transfer from quantum dots (QDs). This relationship is experimentally explored by using six distinct molecular hole acceptors with an 800 meV range in driving force. Specifically, we have investigated ferrocene derivatives with alkyl thiol moieties that strongly bind to the surface of cadmium chalcogenide QDs. The redox potentials of these ligands are controlled by functionalization of the cyclopentadiene rings on ferrocene with electron withdrawing and donating substituents, thus providing an avenue for tuning the driving force for hole transfer while holding all other system parameters constant. The relative hole transfer rate constant from photoexcited CdSe/CdS core/shell QDs to tethered ferrocene derivatives is determined by measuring the photoluminescence quantum yield of these QD–molecular conjugates at varying ferrocene coverage, as determined via quantitative NMR. The resulting relationship between rate and e...
104 citations
TL;DR: In this article, a vertically oriented array of single-crystalline ZnO nanowires was used to increase the external quantum efficiency of solar cells based on PbSe quantum dots.
Abstract: External quantum efficiency in solar cells based on junctions between PbSe quantum dots (QDs) and thin ZnO films is increased by replacing the ZnO films with a vertically oriented array of single-crystalline ZnO nanowires, and infiltrating this array with colloidal QDs. When illuminated with 100 mW/cm2 of simulated solar light, QD-nanowire solar cells exhibited power conversion efficiencies approaching 2%, approximately three times higher than that achieved with thin-film ZnO devices constructed with the same amount of QDs. Significant photocurrent and power conversion improvement with increasing nanowire length is consistent with higher exciton and charge collection efficiencies.
103 citations
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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.
11,071 citations
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.
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...
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